FINAL REPORT Implementation of the EPCC Methodology for ...

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FINAL REPORT Implementation of the EPCC Methodology for Assessment of Functional Stability Mohawk Valley Landfill Frankfort, New York

Prepared by:

10211 Wincopin Circle, Floor 4 Columbia, Maryland 21044 Project Number: ME1165 28 April 2016

Geosyntec Consultants

TABLE OF CONTENTS EXECUTIVE SUMMARY ................................................................................................... 1 ACKNOWLEDGEMENTS .................................................................................................. 6 1.

INTRODUCTION ......................................................................................................... 7

1.1 1.2

1.3

Terms of Reference ....................................................................................................... 7 Technical Background.................................................................................................. 8 1.2.1 Regulation of Post-Closure Care at Municipal Solid Waste Landfills ......... 8 1.2.2 The Evaluation of Post-Closure Care (EPCC) Methodology ....................... 9 Study Overview and Case Study Selection ............................................................... 11

2.

SITE BACKGROUND AND FEATURES OF RELEVENCE ............................... 14

2.1

Site Overview .............................................................................................................. 14 2.1.1 Layout and Physiographic Setting ........................................................... 14 2.1.2 Operational History and Waste in Place ..................................................... 14 2.1.3 Geology and Hydrogeology........................................................................ 15 Landfill Layout and Design Components ................................................................. 17 2.2.1 Liner and Leachate Collection System ....................................................... 17 2.2.2 Leachate Management System ................................................................... 18 2.2.3 Final Cover and Stormwater Management System .................................... 21 2.2.4 Landfill Gas Management System.............................................................. 21 Environmental Monitoring Plan ............................................................................... 21 2.3.1 Groundwater ............................................................................................... 22 2.3.2 Surface Water ............................................................................................. 24 2.3.3 Landfill Gas ................................................................................................ 24 2.3.4 Leachate ...................................................................................................... 24 Landfill Gas Collection System Monitoring ............................................................ 24 Post-Closure Inspection and Maintenance ............................................................... 25 2.5.1 Final Cover System..................................................................................... 25 2.5.2 Stormwater Management System ............................................................... 25

2.2

2.3

2.4 2.5

3.

EVALUATION OF WASTE SOLIDS DECOMPOSITION .................................. 26

4.

END USE STRATEGY FOR THE LANDFILL PROPERTY ............................... 28

5.

FUNCTIONAL STABILITY WITH RESPECT TO LANDFILL GAS ................ 29

5.1

Overview of the Evaluation Process .......................................................................... 29

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TABLE OF CONTENTS (continued)

5.2 5.3

5.4

5.5

5.6 5.7

5.1.1 Background ................................................................................................. 29 5.1.2 Procedural Basis ......................................................................................... 30 Site Features of Relevance to the Gas Module ......................................................... 31 Prerequisites ................................................................................................................ 31 5.3.1 Active LFG Controls and Monitoring Systems in Place ............................ 31 5.3.2 Availability of Site Data ............................................................................. 32 5.3.3 Historical and Current Gas Impacts ............................................................ 32 5.3.4 Standards and Specifications for Gas Control ............................................ 33 First Gas Module Evaluation G1-Y5 (1997) ............................................................. 34 5.4.1 Downward Trend in Methane Collection ................................................... 34 5.4.2 Current Methane Concentration ................................................................. 35 5.4.3 Landfill Gas Generation and Collection Modeling .................................... 35 5.4.4 Outcome and Recommendations ................................................................ 37 Second Gas Module Evaluation G2-Y9 (2001) ......................................................... 37 5.5.1 Downward Trend in Methane Collection ................................................... 38 5.5.2 Current Methane Concentration ................................................................. 38 5.5.3 Comparison to Standards and Specifications for Gas Control ................... 39 5.5.4 Landfill Gas Generation and Collection Modeling .................................... 40 5.5.5 Outcome and Recommendations ................................................................ 41 Transition to Passive Gas Management (2002, Year 10 of PCC) ........................... 41 Gas Confirmation Monitoring ................................................................................... 42 5.7.1 Calculating Time of Travel (TOT) for Gas Migration ............................... 43 5.7.2 Components of Gas Confirmation Monitoring ........................................... 45 5.7.3 Completion of Confirmation Monitoring ................................................... 46

6.

FUNCTIONAL STABILITY WITH RESPECT TO LEACHATE ....................... 47

6.1

Overview of the Evaluation Process .......................................................................... 47 6.1.1 Background ................................................................................................. 47 6.1.2 Procedural Basis ......................................................................................... 47 Site Features of Relevance to the Leachate Module ................................................ 48 Prerequisites ................................................................................................................ 48 6.3.1 Leachate Management and Monitoring Systems in Place .......................... 48 6.3.2 Leachate Management Strategy .................................................................. 50

6.2 6.3


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6.9

6.3.3 Historical and Current Leachate Impacts ................................................... 50 6.3.4 Leachate Data and Sampling Locations ..................................................... 50 6.3.5 Water Quality Standards and Guidelines .................................................... 51 6.3.5 Groundwater Indicator Parameter............................................................... 52 First Leachate Module Evaluation L1-Y5 (1997) .................................................... 53 6.4.1 “Gateway” Indicators of Functional Stability............................................. 53 6.4.2 Evaluation of Potential Threat posed to Human Health and the Environment .................................................................................................................... 55 6.4.3 Outcome and Recommendations ................................................................ 63 Second Leachate Module Evaluation L2-Y10 (2002) .............................................. 63 6.5.1 “Gateway” Indicators of Functional Stability............................................. 63 6.5.2 Evaluation of Potential Threat posed to Human Health and the Environment .................................................................................................................... 65 6.5.3 Outcome and Recommendations ................................................................ 70 Third Leachate Module Evaluation L3-Y19 (2011) ................................................ 70 6.6.1 “Gateway” Indicators of Functional Stability............................................. 71 6.6.2 Evaluation of Potential Threat posed to Human Health and the Environment .................................................................................................................... 72 6.6.3 Evaluation of Leachate Production ............................................................. 77 6.6.4 Outcome and Recommendations ................................................................ 78 6.6.5 Requirements for Confirmation Monitoring............................................... 79 Groundwater Confirmation Monitoring .................................................................. 80 6.7.1 Calculating Time of Travel (TOT) ............................................................. 81 6.7.2 Components of Groundwater Confirmation Monitoring ............................ 83 6.7.3 Completion of Groundwater Monitoring .................................................... 83 Surface Water Confirmation Monitoring ................................................................ 83 6.8.1 Indirect Impacts from Landfill Leakage ..................................................... 84 6.8.2 Indirect Impacts from Leakage from the CWTS ........................................ 86 6.8.3 Direct Impacts from Landfill Seeps ............................................................ 87 6.8.4 Direct Impacts from CWTS Discharge....................................................... 87 Transition to Passive Leachate Management (Future) ........................................... 88

7.

FUNCTIONAL STABILITY WITH RESPECT TO THE FINAL COVER ........ 89

6.4

6.5

6.6

6.7

6.8


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TABLE OF CONTENTS (continued) 7.1

7.2 7.3

7.4

7.5

7.6

Overview of the Evaluation Process .......................................................................... 89 7.1.1 Background ................................................................................................. 89 7.1.2 Procedural Basis ........................................................................................ 89 Site Features of Relevance to the Cap Module ........................................................ 89 Prerequisites ................................................................................................................ 90 7.3.1 End Use Strategy ........................................................................................ 90 7.3.2 Outcomes from Previous Modules ............................................................. 90 7.3.3 Cap Inspection and Maintenance Program ................................................. 91 First Cap Module Evaluation C1-Y5 (1997) ............................................................ 91 7.4.1 Evaluation of Post-Closure Settlement ....................................................... 91 7.4.2 Cap Performance and Integrity ................................................................... 93 7.4.3 Outcome and Recommendations ................................................................ 93 Second Cap Module Evaluation C2-Y9 (2001) ........................................................ 94 7.5.1 Evaluation of Post-Closure Settlement ....................................................... 95 7.5.2 Cap Performance and Integrity ................................................................... 96 7.5.3 Outcome and Recommendations ................................................................ 97 Confirmation Monitoring .......................................................................................... 97 7.6.1 Cap Settlement ............................................................................................ 98 7.6.2 Cap Inspection and Maintenance Program ................................................. 98

8.

SUMMARY AND CONCLUSIONS.......................................................................... 99

8.1 8.2

End Use Strategy......................................................................................................... 99 Landfill Gas Management ......................................................................................... 99 8.2.1 Key Findings ............................................................................................... 99 8.2.2 Confirmation Monitoring.......................................................................... 100 8.2.3 Data Needs ................................................................................................ 101 Leachate Management ............................................................................................. 101 8.3.1 Key Findings – “Gateway” Indicators of Functional Stability ................. 101 8.3.2 Key Findings – Evaluation of Threat to Human Health and the Environment ............................................................................................. 102 8.3.3 Confirmation Monitoring.......................................................................... 103 8.3.4 Data Needs ................................................................................................ 104 Final Cover Settlement and Integrity ..................................................................... 104

8.3

8.4


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8.5

8.4.1 Key Findings ............................................................................................. 104 8.4.2 Confirmation Monitoring.......................................................................... 105 8.4.3 Data Needs ................................................................................................ 105 Transition to Custodial Care ................................................................................... 105

REFERENCES .................................................................................................................. 107 TABLES Table 2-1:

Hydraulic Conductivity of Subsurface Geological Materials

Table 5-1:

Revised EPCC Methodology Gas Module Table E-5-4

Table 6-1:

Evaluation L1-Y5, Summary of Results from Leachate Evaluation (Groundwater)

Table 6-2:

Evaluation L1-Y5, Summary of Results from Leachate Evaluation (Surface Water)

Table 6-3:


Table 6-4:


Table 6-5:


Table 6-6:


Table 8-1:

Summary of Gas Module Evaluations

Table 8-2:

Summary of Leachate Module Evaluation of “Gateway” Indicators

Table 8-3:

Summary of Leachate Module Evaluation of Threat to HHE

FIGURES Figure 1-1:

Performance-Based PCC and Functional Stability

Figure 2-1:

Layout of Case Study Site (2011 Aerial Image)

Figure 2-2:

Simplified Geological Cross Section


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TABLE OF CONTENTS (continued) Figure 2-3:

Section of the Landfill and Subsurface between Route 5S to the Southwest and the Mohawk River to the Northeast

Figure 2-4:

Leachate Collection Pipe

Figure 2-5:

Leachate Management System at the Landfill since 2012

Figure 2-6:

Leachate Management Process Flow and Monitoring Diagram

Figure 2-7:

Final Cover Design

Figure 2-8:

Groundwater and Surface Water Monitoring Locations

Figure 5-1:

Evaluation G1-Y5, Monthly Average Methane Flow

Figure 5-2:

Evaluation G1-Y5, Landfill Gas Generation Potential and Collection

Figure 5-3:

Evaluation G2-Y9, Monthly Average Methane Flow

Figure 5-4:

Evaluation G2-Y9, Landfill Gas Generation Potential and Collection

Figure 5-5:

Development of a Gas Confirmation Monitoring Program based on Layout of POE, POC, and Gas Time of Travel

Figure 6-1:

Site Features of Relevance to the Leachate Module

Figure 6-2:

Evaluation L1-Y5, Leachate BOD Concentration Trend

Figure 6-3:

Evaluation L1-Y5, Ratio of BOD/COD Concentrations in Leachate

Figure 6-4:

Evaluation L1-Y5, Leachate pH

Figure 6-5:


Figure 6-6:


Figure 6-7:


Figure 6-8:


Figure 6-9:


Figure 6-10:


Figure 7-1:

Evaluation C1-Y5, Modeled Post-Closure Settlement Rate

Figure 7-2:

Aerial Image of the Landfill in July 1995

Figure 7-3:

Evaluation C2-Y9, Modeled Post-Closure Settlement Rate


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TABLE OF CONTENTS (continued) Figure 7-4:

Aerial Image of the Landfill in April 2003

Figure 7-5:

Aerial Image of the Landfill in June 2006

APPENDICES Appendix 1:

Waste Sampling and Solids Analysis

Appendix 2:

Landfill Gas Module Evaluation

Appendix 3:

Leachate Module Evaluation

Appendix 4:

Cap Module Evaluation


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EXECUTIVE SUMMARY This final report was prepared by Geosyntec Consultants of Columbia, Maryland for the Environmental Research and Education Foundation (EREF) of Raleigh, North Carolina to describe findings from case study application of the Evaluation of Post-Closure Care (EPCC) Methodology at the closed Mohawk Valley Landfill (MVLF) located near Frankfort, New York. EPCC was developed by Geosyntec for EREF with the aim of providing a technically defensible, performance-based approach for evaluating the site-specific elements of post-closure care (PCC) at municipal solid waste (MSW) landfills regulated under Subtitle D of the Resource Conservation and Recovery Act (RCRA). Subpart F of Subtitle D stipulates that an owner/operator of a closed MSW landfill is responsible for its maintenance, monitoring, and condition for 30 years, or for an alternative period as necessary to protect human health and the environment (HHE). PCC activities include monitoring of leachate and landfill gas (LFG) emissions and potential receiving systems (e.g., groundwater, surface water, soil, and air) as well as maintenance of the cover, leachate, and LFG collection systems. Protection of HHE is demonstrated when potential threats to HHE are minimized to acceptable levels at the relevant point of exposure (POE), which is typically identified as the closest property boundary location at which a receptor could be exposed to contaminants and receive a dose via a credible pathway. Demonstrations are made at the point of compliance (POC), which must be located no further from the landfill than the POE. Consistent with the above, demonstration of no unacceptable threat at the relevant POE in the absence of active care can thus serve as a foundation for demonstrating when regulatory PCC can end. EPCC defines the end of PCC in these terms as ‘functional stability,’ and provides a modular approach for sequentially evaluating the three primary control elements of PCC (i.e., leachate management, LFG management, and cover maintenance) in this context. Once these elements are demonstrated to meet conditions for functional stability, active control and maintenance can be terminated following a confirmation monitoring (CM) program that includes monitoring of groundwater and methane probes to demonstrate that the proposed conditions of passive care or no care are protective. Responsibility for the landfill can then transition from regulated PCC to a custodial care program of land management. Custodial care includes some de minimis level of care to protect against disturbance of buffer zones or passive barriers (mainly the cover), satisfy institutional controls, deed restrictions, or covenants, and facilitate beneficial reuse of the property. By assessing long-term monitoring and management requirements in this way, PCC activities can be demonstrated to be completed, if appropriate, or optimized to focus specifically on providing an environmentally protective level of PCC. The EPCC approach focuses on site-specific leachate and LFG characteristics, the performance of passive control systems, and an evaluation of potential threats derived from the sensitivity of the surrounding environment and a defined end use for the landfill property. Evaluations involve analyzing statistical trends in leachate quality, LFG generation, and landfill settlement to demonstrate that leachate quality is constant or improving, groundwater is not impacted, LFG production is stable or decreasing, and settlement is essentially complete. The evaluations are based on conservative assumptions and driven by data. Proactive data collection is therefore critical for successful application of EPCC at any landfill. Fundamentally, the EPCC framework of data collection and analysis is designed to demonstrate that active leachate and LFG management can ultimately transition to passive care under a non-regulatory custodial care status. A key benefit of EPCC is that all analyses are site-specific; therefore, measures to proactively stabilize waste (e.g., bioreactor operation) or include more sustainable design components (e.g., gravity drains for leachate, alternative all-soil final covers) will be reflected in the outcome. Two key elements of EPCC are that the POE is defined by the ultimate property end use and the potentially ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL-REV1.DOC 1

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iterative nature of PCC system shutdown and CM is built into the process itself. This avoids the need for subjective definitions or categorization of in-situ waste characteristics inherent in other approaches. In conjunction with Waste Management of New York (WMNY), Geosyntec identified MVLF as an ideal case study at which to conduct a series of retroactive functional stability analyses for leachate management, LFG control, and cover stability. The site was selected because it had all the control systems required for PCC under Subtitle D (unusual for a pre-Subtitle D landfill) and a comprehensive dataset dating back over 20 years (again, an unusual feature for an older site). Importantly, working with the New York State Department of Environmental Conservation (NYSDEC), WMNY had already negotiated active control system shutdowns for LFG and leachate management, which had been progressively implemented through the years of post-closure. This added an extra dimension to this study, because the outcomes modeled through retroactive application of EPCC could be directly compared to changes that had already been made; in other words, WMNY and NYSDEC had already implemented a prototype CM approach to support incremental transition from active to passive care. This unique set of circumstances were extremely beneficial to this study in terms of understanding expected outcomes from sequential application of EPCC over a two-decade period. However, this report does not intend to suggest that MVLF is typical of closed Subtitle D landfills. It is designed to provide the industry with an illustration of the types of data needed to complete a performance demonstration and a user’s guide to implementing the EPCC process if said data are available. The facility is a 29-acre MSW landfill on an 80-acre property that operated between the early 1970s and 1991. About 2.2 million cubic yards of MSW were placed in the landfill. Closure construction was completed in 1993, after which the site commenced a 30-year PCC term regulated by NYSDEC in accordance with Section 2.15 of 6CRR-NY Part 360. The final cover is an all-soil design absent a geomembrane barrier. A LFG-to-energy plant operated between 1990 and 2001, after which methane production could no longer sustain plant operations. The site does not have a modern geomembrane liner system; however, the geologic strata underlying the landfill are dense, low permeability glacial till deposits overlying shale bedrock. The lower gray till comprises a de facto liner, with basegrades established to drain leachate to a leachate collection system (LCS) at the downgradient toe of the landfill from where it gravity flows to onsite leachate storage tanks. Until 2012, leachate was hauled off site for treatment and disposal; since then, however, a constructed wetlands treatment system (CWTS) was installed to provide onsite leachate treatment with permitted discharge of treated effluent to the Mohawk River through a control vault and stabilized drainage channel. Groundwater occurs under both confined and unconfined conditions in the area, the latter where bedrock is overlain by glacial till. Groundwater generally flows vertically downward through the till to the top of bedrock and then laterally along the top of bedrock to the river, although groundwater flow can be influenced by the presence of local sand and gravel lenses and alluvial deposits within the upper brown till. The predominant direction of groundwater movement in the unconsolidated units is laterally towards the river. MVLF has been considered an “accidental bioreactor” due to its siting and design allowing subsurface infiltration of groundwater prior to collection in the downgradient LCS. This was intensively investigated under a solids sampling and analysis program conducted during the 2001-2002 timeframe. Although solids sampling is not recommended under EPCC, these existing data were reviewed and analyzed as part of this study with the objective of ascertaining whether they provided valuable information regarding the status of organic and, by association, functional stability. However, the data were found to be inconsistent and of little value in terms of understanding landfill performance, supporting EPCC’s

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position that it is extremely difficult if not impossible to obtain representative solids samples to analyze the relative state of waste degradation within MSW landfills. Routine monitoring data that are useful for this study in term of evaluating functional stability at MVLF have been collected since 1987. The approved environmental monitoring plan (EMP) covers LFG, groundwater, and surface water monitoring as well as analysis of leachate samples. Of unique value, a leachate and LFG database spanning over 20 years was available that allowed a series of functional stability analyses to be performed retroactively approximately five, ten, and 20 years after closure (the precise timing of evaluation events was established following more detailed review of site conditions and operational/PCC history). The focus of each evaluation is to approximate where MVLF is on the functional stability “curve” with respect to the primary components of PCC (leachate management, LFG management, and cap stability). For the purposes of these assessments, the groundwater monitoring component is used to confirm that the functional stability aspects for these primary components have not (and will not) cause an impact above applicable performance standards. Defining the end use of the landfill property is critical in conducting a functional stability analysis since it assigns expected conditions for custodial care and can also define an appropriate POE, which may be different than the property boundary. For simplicity, at MVLF it was consistently assumed in all evaluations that the landfill property will be maintained as green space set-aside with human contact minimized throughout the post-closure period and beyond into custodial care. Specifically, access to the site will be controlled through maintenance of perimeter fencing, institutional controls will preclude the consumption of groundwater or surface water at the site, leachate will continue to be drained passively from the LCS at the base of the landfill and be managed on site, and the existing cover system and other surface features such as the stormwater management system will remain in place and maintained to function as necessary to retain the character of the landscape. This simple end use strategy was effective in this study, allowing demonstration of functional stability with regard to LFG, leachate, and the cap. Two retroactive evaluations of LFG management using EPCC were performed in this study, the first in 1997 (Evaluation G1-Y5, Year 5 of PCC) with a follow up in 2001 (Evaluation G2-Y9, in Year 9 of PCC). Evaluation G2-Y9 showed that active LFG collection was no longer the best available control technology (BACT) and suggested that passive venting could serve as the BACT for residual gas control, supplemented with the methane oxidation capacity of the all-soil cover system. This finding is fully consistent with NYSDEC’s regulation of the landfill in that eliminating active LFG management in favor of passive venting was approved at MVLF in 2002. For this study, a hypothetical CM program was developed to demonstrate the validity of this finding. The POC was assumed as an existing methane migration monitoring probe GP01, located approximately 35 feet from the toe of the landfill in the direction of the nearest potential sensitive receptor (an occupied house), and equidistant from the western property boundary (POE). The duration of CM based on the maximum time of travel for gas migration in the vadose zone from the landfill toe to probe GP01 was 21 months, with monthly monitoring required. Assumed that CM would have been initiated in July 2002, at the time that NYSDEC approved transition to passive gas venting, CM would have been scheduled to be completed in April 2004. WMNY’s monitoring data for this period shows that no gas impacts were detected at monitoring probes; therefore, eliminating active LFG controls and converting to a fully passive venting system in 2002 was an acceptable and sustainable strategy. Conditions for functional stability have been demonstrated with respect to LFG management.


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Two retroactive evaluations of cap settlement were also performed, the first in 1997 (Evaluation C1-Y5, in Year 5 of PCC) with a follow up in 2001 (Evaluation C2-Y9, in Year 9 of PCC). EPCC assumes that significant post-closure settlement will be limited to secondary settlement resulting from waste degradation, which can be modeled based on historical LFG generation and the remaining LFG potential. Significant secondary settlement is assumed complete (i.e., the cap is functionally stable) when it can be demonstrated that the annual rate of settlement is de minimis, that is less than 5% annually relative to the cumulative total post-closure volume reduction at the landfill. Both evaluations projected that functional stability with respect to cap settlement would be achieved no later than 2004, 12 years after closure. This timeframe is supported by findings from the LFG evaluation described above. To confirm that actual cap settlement rates are consistent with modeled predictions, topographic survey data are needed to calculate reductions in the landfill volume over time (which can be translated to settlement). As-built surveys of the landfill cover were conducted as part of closure construction but subsequent surveys have not been conducted, which means that CM for cap settlement cannot be conducted. However, the site is now 12 years past the date at which functional stability with regard to cap settlement was expected, and routine inspection of the cover since closure has not indicated any significant issues related to differential settlement or subsidence leading to surface irregularities, damage, poor drainage, or ponding of water. WMNY reports there has been little to no cap repair required since closure. Therefore, for this study it is reasonable to assume that CM would not have yielded results that conflict with the assessment that the cap is functionally stable. Finally, three retroactive evaluations of leachate management were performed in this study, the first in 1997 (Evaluation L1-Y5, in Year 5 of PCC) with follow ups in 2002 (Evaluation L2-Y10, in Year 10 of PCC) and 2011 (Evaluation L3-Y19, in Year 19 of PCC). The long-term leachate management strategy at MVLF was that leachate would continue to gravity drain from the LCS to onsite storage tanks. However, offsite trucking and disposal of leachate would be abandoned in favor of full onsite management using the CWTS from 2012. Evaluation L3-Y19 in 2011 reflects this planned change in strategy. As with LFG management, it is noteworthy that NYSDEC’s regulation of the landfill in terms of approving transition to a mainly passive CWTS for on-site leachate management is empirically consistent with the recommended approach under EPCC. Key findings include: •

A statistically significant decreasing trend in BOD to a representative value below a threshold of 100 mg/L and an absolute BOD/COD ratio below 0.1 are used as “gateway” indicators of the onset of functional stability conditions in leachate. Overall, the three evaluations showed progressively lower values for all indictors, indicative of increasingly mild leachate and high levels of biodegradation and stability developing within the waste mass. In each evaluation, this step provides a high level of statistical confidence that leachate quality will improve with time.

•

In all evaluations, the principal constituent of concern in terms of leachate quality and allowing transition to passive management was ammonia-nitrogen. Potential threats posed by leachate to HHE were retroactively evaluated based on comparison of leachate quality to applicable water quality standards at the source or POC. Potential pathways for leachate migration used in the evaluations are: (1) leakage of leachate into the subsurface through the base of the landfill and direct migration to groundwater (GW) in the underlying bedrock (Utica Shale, the uppermost aquifer); (2) leakage of leachate into the subsurface through the base of the landfill and indirect migration via the superficial alluvium/brown till to surface water (SW) in the Mohawk River; and (3) direct seepage and runoff of leachate to onsite stormwater ponds. For Evaluation L3-Y19, leakage from the CWTS to superficial GW and direct discharge of treated effluent from the


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CWTS are also applicable. In all cases, progressive and meaningful improvement of leachate quality with time was demonstrated. This is consistent with the gateway indicators and vindication of EPCC’s use of the indicators in this way. •

Time of travel calculations effectively demonstrated that leakage of leachate through the gray till to the bedrock is not of concern – if leakage of leachate through the base of the landfill did occur, it would migrate laterally through more permeable zones in the upper brown till rather than down through the lower gray till. Impacts resulting from a leachate release would thus manifest in SW via superficial GW. This is not a failure in the EPCC process, but rather a successful demonstration of a well-sited landfill for which the very low permeability till provides natural containment to isolate local groundwater resources. As such, the CM program at MVLF should be focused on monitoring SW and superficial GW.

In summary, by 2011 leachate is on the brink of meeting conditions for functional stability. If minor modifications are made to on-site stormwater ponds to function as GW infiltration basins, and the CWTS is modified for passive (internal) discharge via GW infiltration with the Mohawk River recognized as the POE, the only remaining migration route for leachate to the river would be via superficial GW, with ammonia the single remaining analyte of potential concern. Once these modifications have been made and confirmed to be performing as intended, alternative risk-based criteria could be established for ammonia and variances sought from current discharge permit conditions to reflect these modifications and allow transition to post-regulatory custodial care in which no active leachate controls would be required. Another, potentially simpler, option is to continue monitoring for ammonia under the status quo until leachate source concentrations fall below 60 mg/L, the target value for source leachate consistent with meeting conditions for functional stability in SW. In other words, at this concentration, leakage of leachate from the landfill toe drain or CWTS and subsequent migration via superficial GW to the river would not impact GW or SW quality above their respective limit values. At MVLF, custodial care would likely involve providing de minimis oversight of the cap, stormwater swales, ponds, and CWTS; general grounds maintenance; compliance with local land-use requirements, deed restrictions, covenants, and local zoning ordinances; and undertaking typical property management responsibilities such as paying property taxes and controlling access. It is reasonable to expect that such residual care requirements could be provided by a caretaker or landscape gardener outside of the requirements of a Part 360 Permit. The report illustrates that EPCC is relatively easy to use (demonstrating completion of seven evaluations for three different PCC control systems) and that defining functional stability is meaningful: at MVLF, it allows tangible conclusions to be drawn about transitioning active PCC controls to passive management within the 30-year presumptive PCC period. It is recognized that MVLF was fortunate in its construction and siting (e.g., passive drainage can continue for the long term without need for LCS maintenance). This may not be the case at other sites, which would be reflected in an EPCC evaluation performed and could be a limiting factor in defining functional stability. This study marks significant progress towards understanding the impact of site conditions, PCC system design, and availability of data on the EPCC process; however, it is noted that additional experience is still needed on the wider issues that might arise from its broader application. While it is not appropriate to draw firm conclusions about the general efficacy of EPCC, there is reason to be confident that issues will be related to site conditions and/or data availability rather than with the concept of functional stability or the EPCC process itself.


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ACKNOWLEDGEMENTS The principal investigators on this study were: Jeremy Morris, Geosyntec Consultants, Columbia MD Morton Barlaz, North Carolina State University, Raleigh NC The case study site evaluated in this study was volunteered by Waste Management, an EREF industry member. Many people from within the firm gave freely of their time and resources to help collect and interpret site records and analytical data, critically exam analyses performed, and review drafts of the report. In particular, the assistance provided by the following is gratefully acknowledged: Michael Caldwell Chris Prucha David Moreira


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1.

INTRODUCTION

1.1

Terms of Reference

This final report was prepared by Geosyntec Consultants (Geosyntec) of Columbia, Maryland for the Environmental Research and Education Foundation (EREF) of Raleigh, North Carolina. EREF is an independent, grant-making, Internal Revenue Service 501(c)(3) charity whose mission is to develop technological innovations that promote the safety of waste service employees and the public and to improve waste service productivity and resource conservation. Between 2002 and 2006, Geosyntec worked with a multi-disciplinary team on an EREF-funded project to develop the Evaluation of Post-Closure Care (EPCC) Methodology with the aim of providing a technically defensible, performance-based approach for evaluating the site-specific elements of post-closure care (PCC) at municipal solid waste (MSW) landfills regulated under Subtitle D of the Resource Conservation and Recovery Act (RCRA). The Subtitle D regulations were enacted by the United States Environmental Protection Agency (USEPA) and are codified under Part 258 of Title 40 of the Code of Federal Regulations (i.e., 40CFR 258). Subtitle D was developed to minimize potential environmental impacts from MSW landfills, in part by requiring PCC systems and activities at closed landfills to be installed and conducted in a manner that provides long-term protection of human health and the environment (HHE). Specific requirements for PCC are contained in 40CFR §258.61 (i.e., Subpart F of Subtitle D). 40CFR §258.61(b) specifies that PCC must be provided for a 30-year period, which can be decreased or extended by the director of an approved state solid waste regulatory agency such that the changed period is protective of HHE. However, 40CFR §258.61 neither provides nor references a standardized protocol for evaluating the condition of a landfill to demonstrate that the presumptive 30-year PCC period should be decreased or lengthened. EPCC was developed to provide such a protocol. Geosyntec prepared a two-volume EPCC project summary report for EREF, which was published on 6 September 2006. Volume I provides an overview of the project and describes the development of the methodology in terms of the philosophy of the approach and regulatory and technical basis in the context of evaluating threats to HHE posed by potential landfill releases. Volume II comprises a detailed Technical Manual including logic-diagram flow charts and stepby-step instructions for completing an EPCC evaluation. Between 2007 and 2009, EREF funded a Geosyntec team (including representatives from EREF industry members and AquAeTer, a consulting firm) to perform a multi-site case study evaluation to critically examine EPCC and attempt to expose its potential weaknesses. The primary goals of this study were to determine if the data prerequisites outlined in the Technical Manual are presently available at a “typical” MSW landfill site; critically appraise EPCC’s usability in key areas and sensitivity to certain data requirements; assess whether EPCC should be improved to address identified limitations; identify data gaps and data collection needs that impede starting or completing an EPCC evaluation; and assess whether such data gaps constitute ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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“fatal flaws” in EPCC or may be omitted, modified, or replaced by other data. The study, which was published by EREF on 18 March 2011, served to “ground-truth” the state of the industry relative to data availability and helped answer the question “does EPCC work in real situations?” The study concluded that, although further experience is needed, the methodology offers a viable and flexible option for demonstrating long-term threats posed by a landfill based on quantifying its residual emission potential. While significant data are required to make such demonstrations, the study highlighted how taking advantage of proactive data collection plans and good data management strategies can provide immediate cost benefits along the optimization process to functional stability and custodial care, as uniquely offered by EPCC. Several recommendations for updating and improving EPCC were also made based on the findings from this study, and updated or new materials produced accordingly. These materials should be inserted where appropriate into the Technical Manual or used as supplemental resources. Electronic copies of the above reports may be requested from EREF 1. In addition, inquiries into the development, structure, application, and status of EPCC, as well as questions and comments regarding this study, are welcomed and should be addressed to: Jeremy W.F. Morris, Ph.D., P.E Geosyntec (410) 381-4333 [email protected]

or

Bryan F. Staley, Ph.D., P.E. EREF (919) 861-6876 ext. 102 [email protected]

1.2

Technical Background

1.2.1

Regulation of Post-Closure Care at Municipal Solid Waste Landfills

Subpart F of Subtitle D stipulates that an owner/operator of a closed MSW landfill is responsible for its maintenance, monitoring, and condition for 30 years, or for an alternative period as necessary to protect HHE. The basic design elements of engineered landfills include a waste containment liner system to separate waste from the subsurface environment, systems for the collection and management of leachate and landfill gas (LFG), and placement of a final cover after waste deposition is complete. PCC activities required under Subtitle D include monitoring of potential emissions (e.g., leachate and LFG) and receiving systems (e.g., groundwater, surface water, soil, and air) and maintenance of the cover, leachate, and gas collection systems. Protection of HHE is demonstrated when potential threats posed by a closed MSW landfill are minimized to acceptable levels at the relevant point of exposure (POE), which is typically identified as the closest property boundary location at which a receptor could be exposed to contaminants and receive a dose via a credible pathway (USEPA, 1993). Determination of acceptable threat at the POE in the absence of active care can thus serve as a foundation for demonstrating when regulatory PCC can end.

1

Available for download at: www.erefdn.org/index.php/resources/browse


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Based on a recent survey (ASTSWMO, 2013), ten state agencies in the U.S. have promulgated specific PCC regulations or regulatory guidance, with plans underway in a further eleven states. Although Wisconsin has elected to encourage organic stability as a PCC endpoint (WDNR, 2007), some states have made definitive progress in developing regulations requiring that potential threats to HHE and completion of PCC at MSW landfills be assessed on the basis of performance data. Recent notable examples include California, which issued regulations requiring a landfill owner to demonstrate financial assurance (FA) for a minimum of 30 times the annualized PCC costs, but allow a step-down approach to be used to reduce FA starting five years after landfill closure if this is supported by performance data (CalRecycle, 2010). Washington issued revised PCC rules requiring a landfill owner to provide an estimate of the time required for a landfill to reach functional stability after closure (WDE, 2012) and file a covenant, which is intended to provide a method for establishing reuse conditions once the site is functionally stable (after which the solid waste permit is no longer applicable). The covenant must describe with specificity the activity or use limitations on the property. Florida recently issued guidance on using a performance-based approach to demonstrate completion or extension of long-term care (LTC) at older landfills and construction/demolition debris disposal facilities (FDEP, 2016). LTC primarily addresses maintaining the final cover, water quality monitoring, and to the extent that they apply, gas and leachate management. The guidance directly references EPCC and related studies. 1.2.2

The Evaluation of Post-Closure Care (EPCC) Methodology

EPCC provides a modular approach for sequentially evaluating the four primary PCC elements (i.e., leachate management, LFG management, groundwater monitoring, and cover maintenance) in terms of ‘functional stability,’ which describes a closed landfill that does not present an unacceptable threat to HHE in the absence of active care. By assessing landfill monitoring and management requirements in this way, PCC activities can be demonstrated to be completed, if appropriate, or optimized to focus specifically on providing an environmentally protective level of PCC. The approach focuses on site-specific leachate and LFG characteristics, the performance of landfill control systems, and an evaluation of potential threats derived from the sensitivity of the surrounding environment and a defined end use for the landfill property. Application of EPCC requires the end goals and final condition of the landfill to be considered from the outset. The evaluation procedures are based on conservative assumptions, and proposals to modify a PCC monitoring or maintenance activity are driven by data. Proactive data collection is therefore key to successful application of EPCC, which generally involves analyzing statistical trends in leachate and groundwater quality, LFG generation, and landfill settlement to demonstrate that leachate quality is constant or improving, groundwater is not impacted, LFG production is stable or decreasing, and settlement is essentially complete. Modifying or completing an element of PCC requires confirmation of no adverse impacts by monitoring under a conservative sitespecific program. Once all PCC elements are demonstrated to meet conditions for functional stability, responsibility for the landfill can transition from regulated PCC to a custodial care program of land management. Custodial care includes some de minimis level of care to protect against disturbance of buffer zones or passive barriers (mainly the cover), satisfy institutional ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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controls, deed restrictions, or covenants, and facilitate beneficial reuse of the property (Crest et al., 2010). A foundation of the functional stability approach is that impact to HHE is measured at the relevant POE. This is consistent with the U.S. EPA’s guidance for Subtitle D (USEPA, 1993), which states (for example with respect to leachate management) that “concentrations at the point of exposure, rather than concentrations in the leachate collection system, may be used when assessing threats.” Assessment of functional stability is based on conservative assumptions and driven by evaluation of compiled monitoring data. EPCC is advocated by the Interstate Technology and Regulatory Council (ITRC) in their technical guidance document on evaluating, optimizing, and completing PCC (ITRC, 2006) 2. According to ITRC’s recommendation, once functional stability can be demonstrated, the closed landfill may transition to a “Custodial Care” program, which may include some de minimis level of care to protect against disturbance of buffer zones or passive barriers (mainly the cover), satisfy deed restrictions or covenants, and/or facilitate beneficial reuse of the property outside of regulatory PCC.

Figure 1-1: Performance-Based PCC and Functional Stability By assessing landfill monitoring and management requirements in terms of functional stability, PCC activities can be completed, if appropriate, or optimized to focus on providing a level of PCC consistent with site-specific effluent characteristics, the performance of control systems, and evaluation of environmental threat under revised levels of care. Activities and components that are critical to environmental protection and risk reduction are emphasized, so that reductions in effort and expenditure on non-critical components are possible. Figure 1-1 presents a conceptual illustration of a landfill’s step-down progress from active PCC to partially active PCC 2

Available for download at: www.itrcweb.org/guidancedocument.asp?TID=21


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(e.g., constructed wetlands for leachate polishing prior to discharge) to passive PCC (e.g., methane oxidation in cover soils) and transition to custodial care. Note that there is no presumptive timescale on the figure as the time required to move from closure to PCC completion is site specific and based on performance. 1.3

Study Overview and Case Study Selection

In conjunction with Waste Management (WM), the team identified Mohawk Valley Landfill (MVLF) as a candidate case study site at which to conduct functional stability analyses for leachate management, LFG control, and cover stability. The facility is a 29-acre MSW landfill that closed in 1993 under a 30-year PCC term. A LFG-to-energy plant operated between 1990 and 2001, after which methane production could no longer sustain plant operations. The site predates the Subtitle D regulations and does not have a modern liner system and LCS; however, leachate is collected under gravity flow and routed to two onsite leachate storage tanks. Of unique value, a leachate and LFG database spanning over 20 years is available that will allow a series of functional stability analyses to be performed retroactively approximately five, ten, and 20 years after closure. The overall goal of the study is retroactive application of EPCC at MVLF to assess functional stability within three different time horizons. As detailed in subsequent chapters of this report, the precise timing of evaluation events was established following more detailed review of site conditions and operational/PCC history. The focus of each evaluation is to approximate where MVLF is on the functional stability “curve” with respect to the primary components of PCC (leachate management, LFG management, and cap stability). For the purposes of these assessments, the groundwater monitoring component is used to confirm that the functional stability aspects for these primary components have not (and will not) cause an impact above applicable performance standards. 1.4

Primary Site Documentation Available

Various reports and other documentation detailing the design, operation, performance, and closure of MVLF were provided to Geosyntec by WM for review, including: •

Groundwater Boring Logs: Various boring logs and well completion schedules for numerous groundwater monitoring wells installed at the site between 1984 and 1991.

•

Gas Boring Logs: Various boring logs and well completion schedules for numerous LFG extraction wells advanced into the waste in 1988 and 1992.

•

Phase II Hydrogeologic Investigation for the Mohawk Valley Landfill, prepared by Wehran Engineering P.C., dated September 1987 (Wehran, 1987): Partial copy available only.


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•

Engineering Certification Report, 1989-1990 Final Cover Installation, prepared for SCA Services, Inc. by Blasland & Bouck Engineers, P.C. dated October 1990 (BBE, 1990): This report documents final cover construction over approximately 8.6 acres of select sideslope areas that had reached design capacity as of September 1989.

•

Closure Plan for the Mohawk Valley Landfill, prepared for SCA Services, Inc. by Wehran-New York, Inc. dated July 1991 (Wehran, 1991): This report describes the existing design features associated with the facility at that time, including leachate management, stormwater management, soil final cover, and groundwater slurry cutoff wall and collection. The report also describes updates to the closure plan to include active LFG recovery. This document also includes the Post-Closure Plan (PCCP) and approved Environmental Monitoring Plan (EMP).

•

Site Specific Gas Monitoring Plan for Mohawk Valley Landfill and Recycling Center, prepared by Blasland & Bouck Engineers, P.C. dated December 1991 (BBE, 1991): This document contains the gas migration monitoring plan for MVLF, including the layout, well completion details, and boring logs for permanent gas probes installed around the perimeter of the landfill.

•

Certification and Project Summary Report, 1991-1993 Final Cover Installation, prepared for SCA Services, Inc. by Blasland & Bouck Engineers, P.C. dated September 1994 (BBE, 1994): This report documents completion of final cover construction over all areas of the landfill not final capped in 1989-1990.

•

Mohawk Valley Landfill Gas Flare Evaluation Report, prepared by Blasland, Bouck, and Lee, Inc. and included in letter to NYSDEC from WMNY dated March 2002 (BBL, 2002): This report was prepared in response to NYSDEC’s request to evaluate the flare.

•

Test Boring and Waste Sampling Data Report, prepared for Waste Management of New York by McMahon & Mann Consulting Engineers, P.C. dated June 2002 (MMCE, 2002a): This report describes collection of samples for analysis of geotechnical properties and degree of biological degradation, based on the hypothesis that the landfill had achieved an accelerated rate of stabilization as a result of groundwater intrusion.

•

Waste Stabilization Data Report, prepared for Waste Management of New York by McMahon & Mann Consulting Engineers, P.C. dated August 2002 (MMCE, 2002b): This report provides results from analysis of biological degradation parameters collected in June 2002, and summarizes available waste in place and leachate data.

•

Bioreactor Waste Strength Testing Program, prepared for Waste Management, Inc. by Applied Land Science dated 2002 (ALS, 2002): This report provides results from geotechnical testing of waste samples collected in June 2002.


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•

State Pollutant Discharge Elimination System (SPDES) Permit DEC ID #6-212600026/00019, SPDES #NY0257150, Mohawk Valley Landfill and Recycling Center, Frankfort (T), Herkimer County, issued to Waste Management of New York by New York State Department of Environmental Conservation dated 11 December 2009. This permit authorizes a wastewater discharge from an onsite constructed wetland treatment system to surface water at the landfill in compliance with 6CRR-NY Part 750.

•

Constructed Wetland Treatment System Operation and Maintenance Manual, prepared for Waste Management of New York by McMahon & Mann Consulting Engineers, P.C. dated July 2012 (MMCE, 2012): This manual describes the constructed wetland treatment system (CWTS) built to treat and discharge a mixture of groundwater and leachate at the landfill prior to discharge to the Mohawk River.

Many of the above documents include earlier design reports and site investigation studies by reference. Closure and post-closure care at MVLF is regulated under Section 2.15 of the Official Compilation of Codes, Rules and Regulations of the State of New York, Title 6, issued by the Department of Environmental Conservation (6CRR-NY 360-2.15) 3.

3https://govt.westlaw.com/nycrr/Document/I4eaaef3bcd1711dda432a117e6e0f345?viewType=FullText&origination

Context=documenttoc&transitionType=CategoryPageItem&contextData=(sc.Default) ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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2.

SITE BACKGROUND AND FEATURES OF RELEVENCE

2.1

Site Overview

2.1.1

Layout and Physiographic Setting

MVLF comprises a single landfill unit covering about 29 acres of an 80-acre property permitted for waste disposal. The landfill lies near the bottom of the long, gently sloping Dutch Hill south of the Mohawk River. Groundwater flow in the area is generally from uphill elevations in the southwest toward the river in the northeast (Figure 2-1). The site is located outside the Town of Frankfort, New York on Old New York State Highway, Route 5S. Ground surface elevations at the site range from 393 feet MSL at the northern property boundary to 531 feet MSL at the southern boundary along Route 5S

Figure 2-1: Layout of Case Study Site (2011 Aerial Image) 2.1.2

Operational History and Waste in Place

The pre-Subtitle D landfill was operational from the early 1970s and is reported to contain municipal and non-hazardous commercial and industrial solid waste. Various site reports state that most waste was placed after 1976, which is thus taken as the start of landfill operations for ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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the purpose of evaluating landfill performance. Waste disposal ceased in 1991, with closure capping completed during the 1992 and 1993 construction seasons. Although closure capping was not completed until mid-1993, it is reasonable to assign year zero for the EPCC evaluations as 1992, as this is the first year after waste placement ended in 1991. Waste Management of New York (WMNY) acquired the site (via SCA Services, Inc., a second tier subsidiary) in 1984. The volume of waste placed between 1976 and 1991 was estimated by Geosyntec at 2.2 million cubic yards using AutoCAD. This volume was calculated as the difference between the predevelopment grades shown on a Drawing titled “Operation Plan” dated 13 July 1976 (included in MMCE, 2002b) and final capping grades shown in BBE (1994), allowing for the thickness of cover soils. The maximum thickness of waste in place is about 90 feet. Little is known about waste composition, although BBE (1991) reports that prior to 1984 liquid wastes (±20% solids) were accepted and mixed with waste from residential, commercial, and industrial sources. Since 1984, waste composition was about 70% residential, 25% commercial, and 5% industrial with no liquids. Daily cover soil comprised about 14% of total in-place volume. In addition to historical acceptance of liquid wastes, this landfill has been considered an “accidental bioreactor” due to its siting and design allowing subsurface infiltration of groundwater prior to collection in the downgradient leachate collection system. This was intensively investigated under a solids sampling and analysis program conducted during the 2001-2002 timeframe (MMCE, 2002a and b). 2.1.3

Geology and Hydrogeology

The Closure Plan (Wehran, 1991) reports that several hydrogeological investigations have been performed on the site and an adjacent borrow property to the east. Wehran (1991) and MMCE (2002b) provide useful layout figures and properties of subsurface conditions, which are updated and redrawn as Figure 2-2 and Table 2-1. Geologic strata underlying the landfill are as follows: 1. The bedrock underlying the site is Utica Shale, which is exposed in the deep ravine running along the eastern edge of the landfill. The bedrock consists of a dark gray to black, soft to moderately hard fissile shale. In general, the bedrock slopes towards the river, more steeply than the ground surface. Fractures are most abundant in the uppermost five feet. The Utica Shale represents the uppermost aquifer. 2. A dense, dark gray glacial lodgment till overlies the bedrock, ranging in thickness from about 30-40 feet along the southern margins of the site to as much as 70-80 feet along the northern edge. The gray till is fine grained and includes occasional lenses of sand and gravel. These lenses are restricted to the upper ten feet and are not generally continuous. The gray till is exposed in ravines that traverse the site and typically occurs at a depth of about ten feet below the existing natural grade. 3. An upper unconsolidated brown till composed primarily of silt and clay overlies the gray till and occurs at the ground surface except where removed by excavation or erosion.


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This unit averages 10 feet in depth. The brown till is typically fractured in its upper portion and has more granular structure than the underlying gray till. 4. In addition to sand lenses within the till as described above, a second sand unit exists beneath the lowland area north of the landfill adjacent to the river. This unit may be part of an aquifer which occurs in the unconsolidated deposit along the river.

Note: Vertical axis represents feet MSL; Horizontal axis represents feet relative to an unknown datum

Figure 2-2: Simplified Geological Cross Section (Figure B-3 in Appendix G of MMCE, 2002b) Table 2-1: Hydraulic Conductivity of Subsurface Geological Materials Hydraulic Conductivity (cm/s) Unit

Material

Reference: Appendix G, MMCE (2002b) Horizontal Vertical

Reference: Wehran (1991) Horizontal

1

Waste

1×10-3

1×10-3

2

Brown Till

8×10-5

8×10-5

3

More Permeable Materials within Ravines

1×10-3

1×10-3

4

Alluvium

1×10-3

1×10-3

5

Gray Till

7×10-7

1×10-8

9.7×10-7

Upper Bedrock (Uphill Zone) Upper Bedrock (Downhill Zone)

1×10-5

1×10-5

6.8×10-5

1×10-5

9.5×10-6 (range 5.3×10-7 to 5×10-4)

1×10-6

1×10-7

6 7 8

Lower Bedrock

Vertical

10-5

1×10-7 to 1×10-8

Note: Units correspond to Figure 2-2


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Groundwater occurs under both confined and unconfined conditions in the area, the latter where bedrock is overlain by glacial till. In all areas studied by Wehran (1991), the water table surface in the till was located at a higher level than the potentiometric surface in the confined bedrock aquifer. Therefore, the vertical component of flow is downward, in general downward through the till to the top of bedrock and then laterally along the top of bedrock to the river. Groundwater flow can be influenced by the higher permeability upper brown till zone and the presence of local sand and gravel lenses within the tills. As indicated on Figure 2-1, the predominant direction of groundwater movement in plan view in the unconsolidated units is northeast toward the river, with localized flow east and west toward major ravines. Groundwater flow in the bedrock is northward towards and into the river. Recharge to the till is primarily by percolation of incident precipitation, whereas the high Dutch Hill area to the south of the site is thought to provide the primary recharge to bedrock which outcrops in this area. Groundwater discharge from surficial materials occurs as seepage at lower elevations and in the swales that drain the site (hence the Mohawk River as surface water), as vertical seepage to the Utica shale, and as lateral groundwater flow toward the river. 2.2

Landfill Layout and Design Components

2.2.1

Liner and Leachate Collection System

MVLF is a pre-Subtitle D landfill and lacks a composite geomembrane liner system. As noted in Section 2.1.3 above, the landfill underlain by dense glacial brown and gray tills. The upper brown till layer is about 10 feet thick and is less dense and contains a greater proportion of sand and gravel than the thicker lower gray till deposits. Given that the brown till is reported to have been locally removed by excavation, it can be assumed that the gray till serves as the liner. Asbuilt base grades are not available, although the pre-development grades shown in the Operation Plan dated 13 July 1976 (included in MMCE, 2002b) suggest the entire floor of the landfill slopes downward to the northeast. This is consistent with the depiction of the site in several reports (Figure 2-3).

Figure 2-3: Section of the Landfill and Subsurface between Route 5S to the Southwest and the Mohawk River to the Northeast (Figure 3 in Appendix G of MMCE, 2002b) ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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Sources of leachate include infiltration through the cover and lateral groundwater flow in the upgradient waste mass. Leachate migration has been the focus of several studies at the landfill, such that several improvements have been made to contain and control leachate generation. In 1985-1986, a passive leachate collection system consisting of a perimeter leachate collection pipe (LCP) was constructed around the downslope toe of the landfill at the east, north, and west limits of waste. The LCP was installed in a trench excavated through granular materials and the brown till into the gray till (again, supporting consideration that this material serves as the de facto liner). A perforated PVC pipe was placed in the trench and it was backfilled with gravel. A low permeability soil berm was constructed on the downgradient side of the LCP trench (Figure 2-4).

Figure 2-4: Leachate Collection Pipe (Figure 7-1 of Wehran, 1987) Wehran (1991) also reports that pre-landfilling ravines were modified to provide collection of leachate by installing perforated PVC pipe drains prior to waste filling. During construction of the passive leachate collection system, a number of these locations were uncovered and connected to the new leachate collection pipe. 2.2.2

Leachate Management System

The leachate collection pipe drains by gravity toward two underground storage tanks (USTs) designated as East Tank (ETANK) and West Tank (WTANK). Until recently, leachate was pumped from the tanks into a tanker truck and hauled off site for treatment and disposal. The leachate tanks and gravity flow lines are shown on Figure 2-5.


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Figure 2-5: Leachate Management System at the Landfill since 2012 (Figure 1 of MMCE, 2012) ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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During site investigations by Wehran (1987), granular materials were reported within the glacial till immediately northeast of the landfill. A passive groundwater suppression system comprising a cutoff (slurry) wall and dewatering system was installed downgradient of this area in 1989. Groundwater intercepted by the wall flows by gravity through collection pipes and discharges into two USTs designated as Groundwater Tanks or Liquid Storage Tanks (D01) from where it combined with leachate for treatment and disposal (Figure 2-5). In 2012, a constructed wetlands treatment system (CWTS) was designed and installed for onsite treatment of leachate and permitted discharge of treated effluent to the Mohawk River through a control vault and stabilized drainage channel. Transmission of leachate to the CWTS and the discharge outlet to the river are shown on Figure 2-5. The combined liquids flow by gravity to allow passive functioning of the system. A simplified process flow diagram for liquids management at MVLF under the current onsite treatment regime is depicted on Figure 2-6.

Figure 2-6: Leachate Management Process Flow and Monitoring Diagram (Reproduced from p5 of SPDES #NY0257150, dated 11 December 2009)

Treated effluent from the on-site CWTS is discharged to the Mohawk River via Outfall 001. Prior to 2012, the process flow diagram was identical to that shown in Figure 2-6 except that leachate was hauled off site for disposal such that the CWTS (treatment) and Outfall 001 depicted in the figure were absent.


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2.2.3

Final Cover and Stormwater Management System

The final cover design in place at MVLF is depicted on Figure 2-7. The final cover is an all-soil design without a geomembrane component. Sideslopes are approximately 3H:1V, while the average top deck slope is about 8% based on site topography. Landfill gas lateral and header collection pipes are buried in the cover soils. With the exception of topsoil, onsite soils were used to construct the cover.

Figure 2-7: Final Cover Design (Figure 2-1 of Wehran, 1991) As indicated on Figures 2-5 and 2-6, stormwater runoff from the landfill cover is directed via drainage swales to two onsite sedimentation ponds. These ponds discharge through a series of culverts and drainage swales and channels to an unnamed tributary and ultimately to the Mohawk River. 2.2.4

Landfill Gas Management System

Initially, ten vertical wells with passive vents were added in 1988 as an interim gas migration control measure. This was expanded to an active LFG collection system concurrent with closure capping. The LFG system was constructed between July and December 1991, during which time 20 vertical gas extraction wells were added to the wellfield and the existing passive vents converted to extraction wells for a total of 30 wells. The LFG system was connected to an onsite LFGTE plant. The permit to operate the LFGTE plant was issued by NYSDEC on 13 December 1991. 2.3

Environmental Monitoring Plan

Routine monitoring at the landfill has been conducted since 1987. The approved Environmental Monitoring Plan (EMP) is included in the Post-Closure Plan (PCP) for the landfill, which is ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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provided as Section 3.0 of Wehran (1991). The EMP covers LFG, groundwater, and surface water monitoring as well as collection of leachate samples. Routine monitoring of baseline, routine, expanded, and/or alternative parameter datasets is required for groundwater, surface water, and leachate depending on the schedule and analyte list described in Tables 3-1 and 3-2 of the EMP. Updates to the EMP have been enacted since 1991 to comply with the requirements of 6CRR-NY Part 360. 2.3.1

Groundwater

Groundwater monitoring wells at the site are generally installed in clusters of two to four wells. The shallowest well at each location is screened in the till and designated “A.” Deeper wells are screened in the upper bedrock. The groundwater monitoring network at the site (Figure 2-8) comprises 12 well locations: •

Upgradient monitoring well couplets: o MW-6A and MW-6B o MW-7A and MW-7B

•

Proximal downgradient monitoring wells south of Old Route 5S, which are spaced no more than 500 feet apart in accordance with NYSDEC regulations: o MW-4A, MW-4AA, and MW-4BB o MW-5A and MW-5B o MW-10A, MW-10B, MW-10C, and MW-10D o MW-11A, MW-11B, and MW-11C o MW-12A, MW-12BB, and MW-12C o MW-13A, MW-13AA, and MW-13B o MW-14 o MW-15

•

Distal downgradient monitoring wells north of Old Route 5S: o MW-8 o MW-9A and MW-9B

Monitoring well clusters MW-5, MW-12, and MW-13 are installed downgradient of the groundwater cutoff slurry wall and thus serve to monitor the effectiveness of the GSS.


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Figure 2-8: Groundwater and Surface Water Monitoring Locations (Redrawn from Figure 3-1 of Wehran, 1991, with additional wells from Drawing 2 in Appendix A of MMCE, 2012)


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2.3.2

Surface Water

Surface water monitoring locations are shown on Figure 2-8. As shown on Figure 2-5, stormwater runoff from the landfill cover is directed via drainage swales to two onsite sedimentation ponds. Surface water is discharged from the stormwater ponds via Outfalls 002 and 003. Until 2012, the surface water sampling program consisted of composite sampling at each sedimentation pond (termed “SPC”) as well as four surface water locations around the site (S-01 through S-04). Locations S-03 and S-04 represent natural water quality before it enters the site while locations S-01 and S-02 represent water quality after passing through the site. After 2012, the surface water monitoring program also includes Outfall 001, which is discharge of treated effluent from the onsite CWTS to the Mohawk River, a Class B receiving water in this location (Figure 2-6). Routine monitoring data from Outfall 001 are required to be submitted to NYSDEC in a discharge monitoring report (DMR) in accordance with the SPDES Permit. Monitoring of Outfalls 002 and 003 is not required; however, analytical test results for the composite samples taken from these ponds must be submitted annually with the DMR. 2.3.3

Landfill Gas

Potential migration of LFG (i.e., methane) has been monitored at the site since 1987. Initially, this was conducted using barhole probing until October 1989 at which time 19 permanent probes were installed at the property boundary, located at 200-foot intervals along the south, west, and north sides (monitoring on the east side is limited due to the exposed ravine in this area). The EMP required that all probes are monitored quarterly for methane concentration, pressure, and liquid level. 2.3.4

Leachate

The EMP requires collection of leachate samples from the two onsite storage tanks ETANK and WTANK. The tank locations are shown on Figure 2-5. 2.4

Landfill Gas Collection System Monitoring

Following installation of an active LFG collection system in 1991, information on the operation and performance of the system was required to be reported to NYSDEC annually as a permit condition. The annual reports included: •

Hours of operation of the LFG system and total quantity of LFG recovered and electricity generated;

•

Quantity of gas condensate generated; and

•

Summary of sampling data.

The PCP included in Wehran (1991) specified inspection and maintenance activities for the LFG collection system. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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2.5

Post-Closure Inspection and Maintenance

The approved Post-Closure Plan (PCP) included As Section 3.0 of Wehran (1991) specifies a number of inspection, maintenance, and monitoring activities in addition to routine monitoring under the EMP. These include quarterly inspection and evaluation of: •

Site access controls (fences and gates), vegetation, erosion, and evidence of disturbance due to adverse weather events;

•

Cover integrity, vegetation, erosion, seepage, slope stability, subsidence, and settlement; and

•

Runoff controls and the stormwater management system.

2.5.1

Final Cover System

The integrity and effectiveness of the cap is to be inspected and maintained by making repairs as necessary to correct the effects of: •

Differential settlement/subsidence resulting from degradation and consolidation of the waste materials;

•

Surface displacements, irregularities, or other damage leading to poor drainage and/or ponding of water; and

•

Erosion or washout, bare soil, cracks, and holes; and

•

Vegetative damage, distress, or destruction.

Damaged areas require removal of the affected material followed by replacement and regrading to design specifications and contours to restore positive runoff. Surface areas with sparse or missing vegetation require restoration (reseeding and fertilization). 2.5.2

Stormwater Management System

Surface runoff controls, drainage system, and sedimentation basins are to be kept clear of vegetation growth and debris to prevent clogging and ensure free drainage. Eroded or physically damaged sections of surface water channels, swales, and culverts, and other structures are to be repaired by removing loose materials followed by replacement and regrading of the area to specified design contours.


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3.

EVALUATION OF WASTE SOLIDS DECOMPOSITION

MVLF has been considered an “accidental bioreactor” due to its siting and design allowing lateral subsurface intrusion of groundwater along the upgradient (southwestern) landfill boundary. This was intensively investigated under a solids sampling and analysis program conducted during the 2001-2002 timeframe, as discussed by MMCE (2002a and b) and ALS (2002). These documents are listed in Section 1.4. Because these data already exist at MVLF, they were reviewed and analyzed as part of this study with the objective of ascertaining whether they provided valuable information regarding the status of organic and, by association, functional stability. An evaluation of the raw data and pertinent information from the solids sampling and analysis program at MVLF is provided in Appendix 1. 26 small composite samples were collected from 2-4 foot depth intervals within five borings using a 4.25-in hollow stem auger and split spoon sampler. Samples were collected from depths between 10-80 feet (2.5-24 m), although 17 (65%) were collected from shallower than 40 feet (12m). As discussed in Appendix 1, many samples were reported to be relatively dry with presence of significant residual degradable organic matter. A relatively high coefficient of variability of about 50% was observed amongst the moisture content and volatile solids (VS) data, which were uncorrelated to depth. In four of the five borings, all recovered samples contained appreciable biochemical methane potential (BMP) but non-detect concentrations of cellulose, which typically is a major contributor to BMP. It appears that many samples were diluted with soil, possibly due to use of a small sampling device that preferentially selected for materials that would fit into the split spoon sampler and thus would be primarily cover soil and soil-like material not truly representative of the in-situ waste. In general, the results were surprising given the age of the waste at the time of sampling (waste disposal occurred mainly between about 1976 and 1991, meaning the average age of the waste in 2001 was over 17 years’ old). It is also difficult to reconcile the relatively low reported moisture content values with the boring logs from the sampling program, which generally report the waste as “extremely moist” and “wet,” and photographs included the sampling reports showing that many the excavated samples were very wet. Overall, these data are not considered pertinent to the understanding of functional stability at MVLF. Notwithstanding their inclusion herein, it is stressed that solids sampling is not a necessary component of EPCC and that including review of this data in this report is not an indication that Geosyntec would recommend a solids sampling program as part of any functional stability assessment. The fundamental issue is that results from individual samples are unlikely to be meaningful (Barlaz, 2012). A unit volume of waste in a landfill does not exist in isolation. Contaminants leached from the unit volume will pass through a waste column prior to reaching the LCS such that contaminants are diluted or attenuated. As previously noted, there is ample evidence (cit. in Gibbons et al., 2014) to suggest that the bottommost layers of waste in a landfill act as a biofilter with a large attenuating capacity for leachate quality in the basal LCS. Solids ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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samples collected from above the biofilter may be relatively undegraded, but this provides no useful information regarding the residual threat potential of leachate. Similarly, biodegradation and residual LFG potential is most relevant in the context of the configuration of the final cover and the potential for methane oxidation in the cover (Chanton et al., 2011; Caldwell et al., 2016). Again, finding relatively undegraded solids samples does not providing a meaningful indication of the residual threat potential for LFG migration or emission.


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4.

END USE STRATEGY FOR THE LANDFILL PROPERTY

The EPCC approach requires that the end use condition of the landfill property be established as a baseline against which to assess functional stability with regard to proposed optimization or discontinuation of PCC systems or activities. Defining the end use condition also assists in orientating the evaluation in consideration of the long-term plans for the property and the performance requirements for the landfill unit between different modules. For example, the outcome of a leachate evaluation is generally predicated on an assumed level of cap integrity and infiltration control; therefore, modification of the cover system for long-term passive control of gas emissions cannot be considered independently of this need for cover performance. Developing a holistic end use strategy for the site facilitates consideration of interrelated factors outside individual modules and helps govern the choice of intermediate actions to reduce PCC where complete shutdown or elimination is not appropriate. As detailed in Section 3.2 of the EPCC Technical Manual, developing an end use strategy involves defining the long-term condition of the site and its relationship with the surrounding environment (e.g., environmental protection systems, waste containment systems, property uses at the site, etc.) that will form the basis for the evaluations performed. Development of an end use strategy typically considers: •

Applicable local, State, and/or Federal solid waste and “brownfields” regulations;

•

Deed notices, restrictive covenants, zone/ordinance laws, and other applicable institutional controls;

•

Potential liabilities, legal issues, and community concerns and quality of life; and

•

Cost effectiveness and practicality.

At present, there is no documentation of any proactive end use planning at MVLF beyond a closure permit commitment to comply with baseline obligations for restricted use of the property post-landfilling. As a default strategy, it is assumed that the end use of the property will be as green space set-aside (i.e., passive, low impact reuse of the property that recognizes the environmental value of undeveloped land where human contact is minimized through physical and institutional controls). As such, access to the site will continue to be controlled through maintenance of perimeter fencing. Institutional controls will be established that preclude the consumption of groundwater or surface water at the site. The existing cover system and other surface features such as the stormwater management system will remain in place and be inspected, maintained, and repaired as necessary to retain the character of the landscape. In large part, this end use condition helps define potential exposure pathways at the site; therefore, all evaluations must thus be cognizant of, and consistent with, this assumed condition.


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5.

FUNCTIONAL STABILITY WITH RESPECT TO LANDFILL GAS

5.1

Overview of the Evaluation Process

5.1.1

Background

Under RCRA Subtitle D, LFG management is required primarily to control subsurface migration of explosive gases (USEPA, 1991). Evaluation of LFG management seeks to provide a technically defensible assessment of when it would be acceptable to transition from active to passive LFG management and/or reduce or terminate methane migration monitoring based on a demonstration of functional stability (i.e., no threat to HHE in the absence of active LFG control). The main purpose of the EPCC Gas Module is to provide a procedure by which to evaluate modifying or eliminating an active LFG control system. Any modification in the scale and/or intensity of LFG control and/or monitoring would be based on a demonstration that there would be no increased threat to HHE as a result of the modification. The scope of the evaluation depends on a number of interrelated factors, including: •

The end use strategy for the landfill property;

•

The age and size of the landfill;

•

The complexity and scale of the existing LFG control system;

•

The current and historic gas collection rate

•

The extent of LFG control system modification proposed;

•

Cover system properties;

•

Climatic conditions;

•

Geologic, hydrogeologic, and other site-specific conditions such as the nature and proximity of receptors to potential gas migration, emission, and/or odor; and

•

Applicable regulations.

There are also various concerns beyond LFG control regulations that may affect a decision to modify an existing active LFG control system. For example, beyond being installed as a permit condition for control of gas emissions, a LFG control system may have been installed at a landfill unit for a number of reasons (e.g., as part of a renewable energy project, to control subsurface methane migration, or to mitigate gas impacts to groundwater). These should be considered to determine the current and future need for gas management. If modification of a hitherto effective LFG control system is to be successful in the long term, the extent to which current and future conditions at the landfill unit differ from those prior to system modification need to be well defined.


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Evaluation of LFG management seeks to provide a technically defensible assessment of when it would be acceptable to transition from active to passive LFG management and/or reduce or terminate methane migration monitoring based on a demonstration of functional stability (i.e., no threat to HHE in the absence of active LFG control). In the context of estimating the time to achieve functional stability a reduction in the current LFG generation rate to less than 10% of the peak rate is considered to represent a de minimis generation rate and a suitable starting point for determining the potential residual threat to HHE. Once this condition is reached, transition to passive LFG management (including taking advantage of the methane oxidation capacity of landfill cover soils) is reasonable in the significant majority of cases. The actual no-threat condition is then established through site-specific confirmation monitoring. 5.1.2

Procedural Basis

Evaluations performed within the Gas Module are generally based on screening criteria for the effect that the proposed gas management strategy would be expected to have on postmodification performance of the landfill. Due to ongoing updates to EPCC since initial publication in 2006, the systematic procedures for application of the Gas Module are currently provided in three separate technical reference sources. 1. EPCC Methodology Technical Manual (Appendix E of EREF, 2006) Consistent with the RCRA Subtitle D, the original iteration of the Gas Module in 2006 focused on evaluating the potential for impacts due to explosive gas (methane) migration as a result of modification to active LFG controls. To evaluate potential changes, the Gas Module provides qualitative look-up tables of preliminary and secondary screening criteria to conservatively evaluate whether the existing LFG system can be modified or shut down without causing gas migration impacts. Where it remains unclear whether or not a proposed modification is suitable following a simple qualitative evaluation, the module assists the user in making a decision as to whether a more detailed engineering and/or environmental risk evaluation is required. Data and other prerequisites are described in Section 3.4 of the document while evaluation procedures are provided in Section 5. 2. EPCC Methodology Prerequisites Study (EREF, 2011) In a follow-up study performed for EREF by Geosyntec between 2007 and 2009, data collection requirements for application of the Gas Module were updated. Of relevance to application of the Gas Module, this study provided a simplified method for calculating the time of travel for potential gas migration in the subsurface (the basis for gas confirmation monitoring). Details are provided in Section 7 and Appendices 1-4 and 1-5 of the document. 3. EPCC Methodology Gas Module Update (Morris et al., 2012) In recent years, and in particular within the framework of adapting EPCC to the European context, it became clear that it was necessary to broaden the Gas Module’s range of application ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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to include quantitative evaluation of LFG management and monitoring requirements for control of methane emissions and qualitative screening for potential non-compliance issues or impacts due to air quality concerns, for example emissions of non-methane organic compounds (NMOC). This is also important in the context of the EPA’s New Source Performance Standards (NSPS) and Greenhouse Gas (GHG) Reporting Rule. To this end, the Gas Module was further updated in work performed for Suez Environnement CIRSEE by Geosyntec between 2007 and 2011. In this application of the revised Gas Module to MVLF, therefore, the systematic procedures provided in Morris et al. (2012) were generally followed, with direct reference to procedures in EREF (2006) and EREF (2011) where applicable. 5.2

Site Features of Relevance to the Gas Module

Site features of relevance to the Gas Module include: •

Physiographic setting and distance to nearest potential receptor(s)

•

Final cover design

•

Type and operation of LFG management system

•

Waste in place and composition

•

Characteristics of the vadose zone

Details are provided in Section 2. In addition, the assumed end use condition of the landfill property (Section 4) is important. 5.3

Prerequisites

Prerequisites for evaluation of the Gas Module (i.e., modification of the LFG control system and gas migration and emissions monitoring are described in this section. These prerequisites have been modified to reflect the Module’s revision as described above. The six prerequisites for performing an evaluation within the revised Gas Module are reviewed below. It is noted that 1992 represents year zero for PCC at MVLF as waste placement ceased in 1991. Therefore, the meeting of prerequisite conditions for evaluation of the Gas Module is assessed relative to this date. 5.3.1

Active LFG Controls and Monitoring Systems in Place

LFG System: Initially, ten wells with passive vents were added in 1988 as a gas migration control measure. This was expanded to an active LFG system concurrent with closure capping. The LFG system was constructed between July and December 1991 and added 20 wells to the wellfield for a total of 30 wells. The LFG system was connected to an onsite LFGTE plant. The permit to operate the LFGTE plant was issued by NYSDEC on 13 December 1991. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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Migration Monitoring System: Conducted using barhole probing until October 1989 at which time 19 permanent probes were installed at the property boundary, located at 200-foot intervals along the south, west, and north sides (monitoring on the east side is limited due to the exposed ravine in this area). Emissions Monitoring: Not required. The site is not subject to NSPS. 5.3.2

Availability of Site Data

The Gas Module evaluation requires adequate temporal data on LFG generation and composition from a central collection point such as a flare station. This is used to characterize trends in LFG collection and control. It is recognized that at any time in the life of a landfill, less than 100% of the LFG generated can be collected; however, the collectible fraction should be highest and most constant during the post-closure period when a final cover is in place. Therefore, it is reasonable to use as-collected gas data to calibrate modeled predictions. A minimum of three years of monthly methane flow data is recommended, calculated as average total monthly gas flow to the combustion control device multiplied by the methane concentration. At MVLF, various monthly LFG flow and composition (methane and CO2) data were available at the main collection header to the LFGTE plant from 1991 through 2001. No site-specific NMOC data were available. The Gas Module evaluation also requires waste placement records to model gas generation. Although full waste placement records are lacking, a reasonable estimate of the volume of waste in place was available for gas modeling to compare to measured gas collection rates. Little is known about waste composition, beyond the site being permitted for MSW disposal. Leachate recirculation has never been practiced; however, high-liquid wastes and sewage sludge were historically accepted and considerable subsurface infiltration of groundwater has reportedly occurred. The solids sampling program in 2001-2002 (Section 3) also observed very wet waste in drilling cuttings. As such, it is reasonable to assume that the moisture content of in-place waste is relatively high. In general, there is good availability of critical information regarding the layout of the landfill and network of POC monitoring probes as well as the extent of the buffer zone between the landfill and property boundary (in the context of gas migration at MVLF, the property boundary is both POC and POE) and locations of potentially sensitivity receptors to gas migration. Sufficient geologic and hydrogeologic information is available to adequately characterize vadose zone conditions and calculate a time of travel (TOT) for gas migration to the POC. 5.3.3

Historical and Current Gas Impacts

To proceed with an evaluation, there should be no current compliance issues related to gas migration at the landfill based on at least four consecutive quarters of monitoring data. Based on site reports, there have been no gas migration issues since closure of MVLF in 1992. Further, ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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there is no evidence of gas (i.e., VOC) impacts to groundwater (per the screening procedure for compliance provided in Section 3.4.4 of the Technical Manual). To proceed with an evaluation, there should also be no current compliance issues related to odors or surface emissions at the landfill. Based on site reports, there have been no odor complaints since closure of MVLF in 1992. Surface emission monitoring (SEM) is not required at the site. 5.3.4

Standards and Specifications for Gas Control

A final prerequisite is to identify national or site-specific standards for gas migration and emissions, along with the nationally-accepted best available control technology (BACT) for gas control at landfills. MVLF predates Subtitle D and is not subject to any national or state standards or limits on surface emissions. Nevertheless, as rules mandating the control of LFG but which are outside of Subtitle D must generally be complied with when evaluating the suitability of modifying an active LFG system, these are briefly examined at MVLF. These are: •

The NSPS Regulation (USEPA, 1996), which is applicable to landfills above a threshold design capacity of 2.5 million Mg. At sites subject to NSPS, active LFG controls must be installed and remain operational until generation of total non-methane organic compounds (NMOC) in gas is estimated to fall below 50 Mg/year for three consecutive years. Site specific NMOC concentration data can be collected in accordance with U.S. EPA protocols; alternatively, a default concentration of 4,000ppmv as hexane is assumed.

•

The 2010 Mandatory Reporting of Greenhouse Gases (GHGs) Rule, which is applicable to landfills generating 25,000 Mg of CO2 equivalent (tCO2e) per year (40CFR Part 98, Subpart HH). Using LandGEM, this equates to a total LFG generation rate of about 240 scfm at 50% methane.

Few definitive BACT threshold values have been promulgated, either in the U.S. or internationally. BACT as a limiting factor for gas control is often implied, but no guidance on what constitutes BACT is provided. In some cases, a de minimis gas flow rate representing the limitation for specific BACT gas controls may be specified. For example, guidance issued in France suggests that it is acceptable to consider eliminating an active LFG system if gas production falls below 100m3/hour (approximately 60 scfm), assuming 50% methane content (Bour et al, 2005). This could be considered equivalent to a BACT specification (i.e., a flare is the BACT if gas production exceeds this rate). The same guidance suggests natural attenuation/passive venting (i.e., the absence of gas control) as appropriate when the overall methane emission flux (i.e., methane generation divided by surface area of the cover) falls below 5m3/ha/hour (1.2 scfm/ac). More recently, the Irish EPA (2011) advised that fully passive controls can constitute the BACT once methane flow is consistently below 60 scfm. Below this value, it is argued that maintaining uninterrupted operation of an active system such as a small utility flare will become so difficult that the amount of downtime (i.e., periods of no


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treatment of emissions) experienced will outweigh any remaining benefits that active control offers over passive control. The U.S. EPA’s qualitative process for selecting BACT for LFG control at landfills with low residual gas levels is described in USEPA (2011a). In brief, this suggests: (1) identify all available control technologies; (2) eliminate those technically infeasible on a site-specific basis; (3) evaluate and rank remaining controls based on environmental effectiveness; (4) evaluate cost effectiveness of controls; and (5) select BACT. A state-of-the-practice review of BACT for GHG control at landfills is provided in USEPA (2011b). 5.4

First Gas Module Evaluation G1-Y5 (1997)

Completing an evaluation within five years of entering PCC should provide a useful “first look” at how the site is performing and whether sufficient data are being collected. This helps set expectations and make informed decisions about the timing and potential scope of future modifications that will be possible. As such, entering this evaluation with the perspective of an “EPCC Consultant” with the information available in 1997, it is anticipated that Evaluation G1Y5 would serve primarily to suggest when the next follow up evaluation should be scheduled. Raw data, input assumptions, and detailed results from Evaluation G1-Y5 are provided in Appendix 2. A summary of pertinent findings is provided in the remainder of this section. 5.4.1

Downward Trend in Methane Collection

For Evaluation G1-Y5, LFG flow and methane content data at the main header were consolidated into 48 monthly average methane flow data for the period September 1993 to August 1997. Data prior to September 1993 were not used as final construction of the closure cap was reportedly only completed in the “summer construction season” of 1993, meaning that significant disturbance to the LFG system would be expected prior to this date. This is corroborated by peak flows being measured in 1994, one year after completion of closure capping. As illustrated on Figure 5-1, a reasonably well correlated (R2 > 0.5) downward trend is evident based on the best-fit linear regression. The statistical validity of the downward trend was confirmed using Sen’s test, a simple non-parametric trend estimator which is robust to outliers, missing data, and non-detects (Sen, 1968). A statistically significant downtrend in methane flow from the landfill provides confidence that LFG generation will not increase in the future given landfill conditions such that conclusions based on current and historic gas data and LFG system performance will remain valid in the future.


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Figure 5-1: Evaluation G1-Y5, Monthly Average Methane Flow

5.4.2

Current Methane Concentration

In addition to demonstrating a downward trend in methane flow to the flare, the methane flow rate to the flare was calculated as the 95% upper confidence limit (UCL) to the mean of the data. This statistically representative flow rate was 216 scfm in August 1997, which is twice the typical industry standard of 100 scfm as a practical lower-bound cutoff flow rate for active flare operation. In other words, active LFG control remains the BACT for gas management at MVLF in 1997. 5.4.3

Landfill Gas Generation and Collection Modeling

This step is intended to be used for planning, mainly to set expectations for the timing and scope of eliminating/modifying LFG controls, and as a check on the actual level of gas control achieved. Gas generation models are recommended to estimate when gas generation rates are likely to be low enough to implement a reduced or lower level of gas control. It is recognized that such models are imperfect and comparisons between models and actual collection may be misleading (under or over predict gas generation). The U.S. EPA’s LANDGEM (USEPA, 2005), for example, was designed to predict the volume of gas that can be collected as opposed to total gas production. Implicit in LANDGEM is the fact that the LFG collection efficiency is below 100%. LANDGEM also assumes that methane production commences without a lag time, which results in earlier gas production than is the case in the presence of a lag time (Barlaz, et al., 2009).


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Monthly LFG flow data were consolidated into four annual average methane flow data for 1994 (peak) through 1997. A strongly correlated exponential best-fit trend line to the data is evident (orange markers and line, Figure 5-2).

Figure 5-2: Evaluation G1-Y5, Landfill Gas Generation Potential and Collection

LFG generation in terms of expected collectable flow (blue line) and generation potential over a 100-year period from initial site operation (green line) were modeled using a specially modified version of LANDGEM developed by Geosyntec to allow greater flexibility in analysis. For this initial analysis, default input values from the EPA’s AP-42 document (USEPA, 1995) were assumed for the methane generation potential (L0 = 100 m3/Mg), methane content (50%), and mean collection efficiency (75%). The decay constant (k) was assumed as 0.08/year rather than the AP-42 default based on visual comparison to the best-fit exponential trend line to the data. This value is also consistent with values proposed for landfills such as MVLF that are reported “wet” during operation (Tolaymat et al., 2010), which is appropriate given the reported history of groundwater infiltration at MVLF. Although full waste placement records at MVLF are lacking, a reasonable estimate of the volume of waste in place between original basegrades and final cover grades was calculated as 2.2 million cubic yards (based on AutoCAD computations by Geosyntec in 2002). From this, it ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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is conservatively assumed that about 1.7 million Mg of waste was placed in the landfill over a 16-year period spanning January 1976 through December 1991. Data on U.S. waste generation rates between 1975 and 1990 (USEPA, 2011c) were used to model growth in the average annual waste disposal rate during this period. 5.4.4

Outcome and Recommendations

As indicated on Figure 5-2, the main result of Evaluation G1-Y5 is that the estimated timeframe to achieve functional stability based on meeting the de minimis residual LFG generation/potential criteria ranges from 2005 (i.e., year 13 of PCC) based on measured LFG collection data to 20152018 (i.e., Year 26 of PCC) based on modeled predictions. It is noted that the earlier timeframe is based on site-specific data, which likely represents the more accurate prediction of the future collectability of LFG. Based on this, and again from the perspective of the EPCC Consultant in 1997, it would likely be recommended that a follow-up Gas Module evaluation be performed no later than 2005. No modification or scaling back of LFG control or monitoring is appropriate at this time. 5.5

Second Gas Module Evaluation G2-Y9 (2001)

By 2000, ongoing operation and monitoring of the LFG system and LFGTE plant showed that WMNY was experiencing difficulties in operating the LFGTE plant, despite having a full-time employee on site as operator and wellfield technician. For example, the 2000 Annual Report for the plant (dated 16 February 2001) states: “Both engines were operated between 50% and 90% load until 1 May 2000, [when] Engine #1 was shut off due to lack of landfill gas available… currently operating one engine between 75% and 95% load.” Having invested in an active wellfield and twin-engine LFGTE plant with full-time operator, and having secured energy sales contracts, it seems likely that WMNY would attempt to maximize LFG recovery and electricity output from the plant. This is supported by the fact that WMNY reported 99.7% online operation of the LFGTE plant during 2000, with minor downtime associated with routine maintenance events only. In November 2001, WMNY submitted notification to NYSDEC that “…due to the decreasing quantity of landfill gas being generated at the closed landfill (approximately 120 cfm), we can no longer effectively operate the plant…” and would transition to using the existing permitted utility flare and associated blower for active control of LFG at the site. Soon after, WMNY informed NYSDEC that they would begin to evaluate the feasibility of permanently decommissioning the LFGTE plant in favor of alternatives for LFG control, including continued active flaring, passive flaring, or passive venting. In the context of this retroactive study, it is assumed that WMNY would have responded to the above situation by retaining the EPCC Consultant to evaluate the feasibility of alternative LFG controls in August 2001, exactly four years after the initial evaluation and four years ahead of the anticipated schedule. This will be denoted as the second Gas Module evaluation, occurring in 2001 in Year 9 of PCC (Evaluation G2-Y9). ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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Raw data, input assumptions, and detailed results from Evaluation G2-Y9 are provided in Appendix 2. A summary of pertinent findings is provided in the remainder of this section. 5.5.1

Downward Trend in Methane Collection

For Evaluation G2-Y9, LFG flow and methane content data at the flare were consolidated into 96 monthly average methane flow data for the period September 1993 to August 2001. A strongly correlated (R2 > 0.8) downward trend is evident based on the best-fit exponential regression line (Figure 5-3).

Figure 5-3: Evaluation G2-Y9, Monthly Average Methane Flow

The statistical validity of the downward trend in methane flow was again confirmed using Sen’s test. Based on this, there is a very high level of confidence that LFG generation will not increase in the future. 5.5.2

Current Methane Concentration

In addition to demonstrating a downward trend in methane flow to the flare, the current methane flow rate was calculated as the 95% upper confidence limit (UCL) to the mean of the four most recently collected monthly flow data. This statistically representative flow rate was 93 scfm in August 2001, down from 154 scfm only a year earlier and 216 scfm in August 1997 during Evaluation G1-Y5.


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5.5.3

Comparison to Standards and Specifications for Gas Control

No emission standards or best available control technology (BACT) specifications are enforced at MVLF; therefore, formal comparison to such cannot be made. NYSDEC is empowered to approve elimination of active gas controls on the basis that a persuasive technical demonstration has been made that alternative gas controls will be protective of HHE. Nevertheless, the following observations can be made with regard to the suitability of eliminating active LFG control in the hypothetical context of NSPS and the GHG Rule, and transitioning to passive measures as the BACT for LFG control at MVLF: 1. NSPS allows active LFG control to be eliminated once site-wide NMOC emissions are below a 50 Mg/year threshold for three consecutive years (USEPA, 1996). Site-specific NMOC data are not available at MVLF; however, taking the default value of 2,420 ppmv from AP-42 (USEPA, 1995) yields 2002 as the third consecutive year in which modelled NMOC emissions would be below 50 Mg. 2. Using LandGEM, the annual 25,000 tCO2e threshold for mandatory control of LFG to mitigate GHG emissions (as required per the GHG Rule, 40CFR Part 98 Subpart HH) equates to a total LFG generation rate of about 240 scfm at 50% methane. Measured gas flows at MVLF were below this threshold by 2000. 3. Few definitive BACT threshold values have been promulgated, either in the U.S. or internationally. However, a useful guidance issued by the Irish EPA (2011) advises that fully passive controls can constitute the BACT once methane flow is consistently below 60 scfm. At MVLF, the methane flow of 93 scfm in 2001 is fast approaching the Irish EPA threshold value; indeed, extrapolation of the post-1998 data on Figure 3-3 suggests the methane flow rate would fall below 60 scfm by the end of 2001. At this time, active combustion of LFG will likely cease to represent the BACT, meaning an alternative passive method of gas control should be established. 4. The U.S. EPA’s process for selecting BACT for LFG control at landfills with low residual gas levels is described in USEPA (2011a). In brief, this suggests: (1) identify all available control technologies; (2) eliminate those technically infeasible on a site-specific basis; (3) evaluate and rank remaining controls based on environmental effectiveness; (4) evaluate cost effectiveness of controls; and (5) select BACT. This procedure was largely followed in the negotiation to eliminate active LFG control between WMNY and NYSDEC in 2002 (see Section 5.6). Therefore, it is reasonable to assume that passive venting could be demonstrated as the primary means of residual gas control supplemented with the methane oxidation capacity of the all-soil cover system as discussed by Caldwell et al. (2016). In summary, all currently available protocols and standards would point to elimination of active LFG control in favor of passive controls as the appropriate course of action at this stage.


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5.5.4

Landfill Gas Generation and Collection Modeling

LFG flow data at the flare were consolidated into eight annual average methane flow data for 1994 (peak) through 2001. A strongly correlated exponential best-fit trend line to the data is evident (orange markers and line, Figure 5-4).

Figure 5-4: Evaluation G2-Y9, Landfill Gas Generation Potential and Collection

LFG generation in terms of expected collectable flow (blue line) and generation potential over a 100-year period from initial site operation (green line) were again modeled using a specially modified version of the U.S. EPA’s LandGEM. The assumed methane content remained as 50%, consistent with AP-42 and reported gas composition data. The assumed collection efficiency remained at 75%, consistent with AP-42 and conservatively lower than values reported for landfills with final covers and active LFG control from a recent state-of-the-practice study (Barlaz et al., 2009). Iterative curve fitting was used to adjust the methane generation potential (L0) and decay constant (k) such that modelled results best mirrored the best-fit exponential trend line to the site data. Based on this, final input values were selected as L0 = 80 m3/Mg and k = 0.135/year. The L0 value is 20% below the AP-42 default value for MSW, which was shown by Staley and Barlaz (2009) to be relatively common. The k value is consistent with upper-bound ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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values reported for very wet landfills and bioreactor operations (Tolaymat et al., 2010) and also matches the value independently suggested by a consultant during a third-party review of the site gas model a number of years ago. As indicated on Figure 5-4, under Evaluation G2-Y9 the estimated timeframe to achieve the conditions for functional stability based on the de minimis threat condition for LFG is now 2002 to 2007 (i.e., between years 10 and 15 of PCC). The earlier date is more likely based on direct linear extrapolation of the site data (black dashed line on the figure). 5.5.5


Evaluation G2-Y9 shows that functional stability has been met or will be in the very near future. The LFGTE plant cannot function viably given existing gas flows. From the perspective of the EPCC Consultant in 2001, the likely conclusion would be that the BACT for LFG control is no longer an active system but would be better achieved through passive measures. In this retroactive evaluation, therefore, it is recommended that WMNY petition NYSDEC to immediately decommission and dismantle the LFGTE plant and to temporarily modify the gas wellfield such that each well would be able to vent passively. A screening process to review the need for Confirmation Monitoring (CM) after tentatively deciding to modify an active LFG system is provided in Section 5.2 of the EPCC Technical Manual, and would typically be followed. However, for this study it is assumed that a CM program for methane migration monitoring is required. Therefore, all components of the active LFG system (i.e., wellheads, header/lateral pipes, blower, and flare) should be disconnected but remain in place subject to completion of CM, which will serve to demonstrate that performance of the passive venting system is appropriate and protective of HHE. 5.6

Transition to Passive Gas Management (2002, Year 10 of PCC)

For interest, a brief overview of the actual negotiation that WMNY entered into with NYSDEC to transition to passive gas management is summarized in this section. Although this of course took place independent of an actual EPCC evaluation, it closely mirrors the type of negotiation that would be expected following a demonstration that passive gas management represents the BACT at a landfill. In 2002, after commissioning a feasibility study of alternatives for LFG control, including continued active flaring, passive flaring, and passive venting, WMNY decided that passive venting was most appropriate. Thereafter, WMNY entered into a long back and forth communication with NYSDEC regarding the authorization process for decommissioning the active LFG system, which was far from straightforward. A brief summary is provided below: •

March 2002: WMNY requested approval to make change to LFG management, based on the Mohawk Valley Landfill Gas Flare Evaluation Report (BBL, 2002) that recommended that existing active LFG system be shut down and remaining LFG wells converted to passive vents by removing wellheads and replacing with gooseneck pipes.


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•

March 2002: NYSDEC responded that “while vents are a common method of handling landfill gas, in this case, they do raise some questions” with regard to variances from the originally permitted closure design (Wehran, 1991), which were only allowed because MVLF was closed with an active LFG system. Specifically, these related to inclusion of a gas venting layer below the cap and a gas cut-off trench on the south side of the landfill in the original closure design. NYSDEC was concerned whether an evaluation had been performed to determine if the passive vents would work without the gas venting layer and why the cut-off trench would not be required in the absence of active gas control.

•

June 2002: WMNY countered that passive venting would be a feasible means of LFG control because conditions at MVLF had changed considerably relative to the time the original permit conditions were imposed. Specifically, LFG generation was substantially lower than predicted, 13 wells had been added in 1997 but did not provide a sustained increase in gas yield (indicating that LFG generation is much lower than previously assumed), and having more wells (31 versus 18 at the time of original permit writing) to convert to vents would provide sufficient preferential flow for gas. As such, the need for a cut-off trench no longer existed. WMNY would continue to provide migration monitoring as a means of ensuring compliance with gas control requirements, and on which to based decisions for mitigation measures.

•

June 2002: NYSDEC conditionally approved the proposed venting system, stating that they “…reserve the right to require additional steps, including the previously required cut-off trench, if it was apparent that such steps were needed.”

Work to decommission the LFGTE plant in order to request a release of the PCC financial assurance (FA) requirements for the facility, and full transition from active LFG control to a passive venting system was completed in July 2002, as described in a letter of notification from WMNY to NYSDEC dated 26 July 2002. The final stipulation from NYSDEC about conditional acceptance of the gas control modifications is fully consistent with Confirmation Monitoring (CM) in the context of an EPCC evaluation. As described in the section below, CM provides the monitoring data that will make apparent the suitability of the new gas venting system or the need to reinstate the level of gas control that was previously required. 5.7

Gas Confirmation Monitoring

The guiding philosophy behind developing a CM program is that, where a high level of confidence exists that implementing a proposed strategy to modify PCC presents a low or negligible threat to HHE, this should be demonstrated directly by means of additional monitoring rather than using a more costly and time-consuming risk modeling approach. CM is considered to provide an “early warning” system in which it is assumed that any subsurface gas migration following modification to active LFG controls will be rapidly detected. In this way, appropriate action can be taken before manifestation of significant gas impacts and potential development of ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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a non-compliance situation if it transpires that the previous evaluations did not adequately predict the behavior of the landfill. For this reason, the CM program must include a contingency plan for reacting to trigger conditions. At the highest level, this includes re-instating the previous level of LFG control, which requires that the conversion of gas wells to passive vents does not involve irrevocable removal of wellheads. Following completion of CM, PCC in the Gas Module can be terminated and any gas-related cover monitoring and maintenance activities provided via the Cap Module. Consistent with the assumed end use condition at MVLF, however, no changes should be made to the existing cover system or property maintenance obligations. 5.7.1

Calculating Time of Travel (TOT) for Gas Migration

The current procedure for establishing a CMP based on calculating TOT for gas migration in the Gas Module is described in Section 5.3 of the EPCC Technical Manual. In brief, maximum and minimum TOTs for gas migration are calculated based on one-dimensional application of Darcy’s law for advective flow in the uppermost porous media under an assumed minimum and maximum pressure gradient, respectively, from the landfill toe to a POC monitoring probe in the direction of the shortest distance to the property boundary. For simplicity of application, Table E-5-4 of the Technical Manual in EREF (2006) provides a range of TOTs (per 100-ft horizontal travel distance) based on a reported maximum hydraulic conductivity in the vadose zone and measured maximum internal gage pressure in the landfill. If the gas POC is further than 100 feet from the toe, the relevant TOT value is simply multiplied accordingly to derive the necessary TOT; this procedure is extremely conservative given that the influence of the advective pressure gradient will decease inversely with distance from the landfill. As originally written, measurements of internal gas pressure in the WMU are essential for calculating a gas migration TOT. However, these data are rarely, if ever, collected, and were not available at MVLF. In conducting this study, the modified screening approach for Table E-5-4 from EREF (2011) was used. This approach brackets near-zero and instability-causing gas pressures to define the duration and frequency of gas confirmation monitoring based on upperand lower-bound TOTs, respectively. The minimum recordable internal gage pressure is set at one inch of water column (1 in-w.c.), because it is reasonable to assume that driving pressures lower than this value will not result in significantly different rates of gas migration. Therefore, in the absence of actual gage pressures, the table assumes a default maximum TOT per 100-ft travel distance relative to the maximum vadose zone hydraulic conductivity, k, reported at the site. The maximum TOT is then used to establish the duration of CM, based on the assumption that a gas plume would not move slower than under these conditions (i.e., CM would detect a gas plume if it were to migrate). The maximum TOT is cut off at 10 years for 100 ft; it is assumed that subsurface gas migration at a rate slower than this from the time that a screening evaluation suggests that modification to LFG controls is appropriate will not be cause for concern because the low hydraulic conductivity of ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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the vadose zone will tend to drive LFG issues at the site to manifest as surface emission exceedances or visible vegetative stress (noticeable under cover maintenance) rather than offsite migration. Indeed, where k ≤ 1 × 10-5 cm/s, no CM is required because the expected rate of gas migration would be de minimis and LFG issues would not manifest as offsite migration. The maximum reasonable internal gage pressure is set at 10 in-w.c., based on independent landfill closure design calculations by Geosyntec that showed that geosynthetic cover system stability typically falls below a factor of safety of 1.0 if gas pore pressures are elevated above 812 in-w.c. In other words, before a sustained pressure of 10 in-w.c. were actually encountered at a geosynthetics capped landfill, significant cover system instability and potential failure conditions would likely be noticed. At a soil-capped landfill such as MVLF, such elevated pressures could likely not arise due to venting through the cover. In the absence of actual gage pressures, the table assumes a default minimum TOT per 100-ft travel distance relative to the maximum vadose zone hydraulic conductivity reported. The minimum TOT is then used to establish the frequency of CM, based on the assumption that a gas plume would not move faster than under these conditions (i.e., CM should not fail to detect a gas plume before it had travelled much beyond the POC, at which point rapid corrective action such as re-ignition of an active LFG system could be implemented to prevent significant migration to the property boundary). Estimate Time to Reactivate Active LFG Controls: It was assumed that the time required to reactivate the existing LFG system, tREACT, would be equal to the default period of 10 days (per Section 5.3.2 of the EPCC Technical Manual). Calculate TOT for Gas Migration: As described in the introductory section, the landfill is underlain by brown till with low horizontal hydraulic conductivity (k = 8 x 10-5 cm/sec). However, the till is interlaced with layers of more permeable materials (k = 1 x 10-3 cm/sec), particularly within ravines at the edge of the property where gas migration is of interest. As shown in Table 5-1, migration through the brown till is not of concern as the permeability of this layer is lower than the threshold for CM. Therefore, the gas migration TOT is assessed based on the potential migration pathway via the more permeable layers. The maximum and minimum TOT per 100 foot horizontal distance in these layers is 5 years and six months, respectively (as indicated by the red box on Table 5-1).


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Table 5-1: Revised EPCC Methodology Gas Module (Modified from Table E-5-4 of EREF, 2006, as revised in Table 6-2 of EREF, 2011) Max. Vadose Zone Hydraulic Conductivity, k (cm/s) -2

Time of Travel per 100 ft Horizontal Distance Internal Gage Pressure Reading (in.-w.c.) 1 5 10 6 months

30 days

15 days

-2

-3

5 years

12 months

6 months

-3

-4

10 years

10 years

5 years

-4

-5

10 years

10 years

10 years

> 5 x 10

5 x 10 - 5 x 10 5 x 10 - 5 x 10 5 x 10 - 5 x 10 -5

< 5 x 10

GAS CONFIRMATION MONITORING NOT REQUIRED

Note: Default values to be used where site-specific measurement is not undertaken. Default maximum TOT is based on internal gage pressure of 1 in.-w.c. Default minimum TOT is based internal gage pressure of 10 in.-w.c.

5.7.2

Components of Gas Confirmation Monitoring

As shown in Figure 5-5, the property boundary (GAS POE) in the direction of the nearest potential sensitive receptor (occupied house) is approximately 70 feet from the toe of the landfill. Gas monitoring probe GP01 exists in an approximate straight-line path between the landfill and the house about halfway (35 feet) between the landfill toe and the property boundary. The probe was installed to a depth of nine feet below ground level (bgl) and screened to monitor the higher permeability materials in the vadose zone at 4-9 feet bgl. This probe represents the POC for CM.

Figure 5-5: Development of a Gas Confirmation Monitoring Program based on Layout of POE, POC, and Gas Time of Travel


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Therefore, with reference to developing a Gas CM program in relation to the maximum calculated TOT, TOTWMU-WELL and TOTWELL-REC equal 1.75 years (i.e., 35/100*5). TOTWMU-REC equals 3.5 years (i.e., 70/100*5). Maximum TOTs are used to define the duration of CM. The minimum calculated TOTs are TOTWMU-WELL = 2.1 months (i.e., 35/100*6), TOTWMU-REC = 4.2 months, and TOTWELL-REC = 2.1 months. Minimum TOTs are used to define the frequency of CM. TOTWMU-WELL > tREACT and TOTWMU-REC > 60 days; therefore, the Gas Module evaluation may proceed past this step (i.e., the travel times to the probes and receptor in relation to the time necessary to reestablish active LFG controls are not as short as to disqualify implementing the strategy of transitioning to passive gas management). Establish Confirmation Monitoring Frequency: To calculate the required CM interval, the most stringent criterion that applies is that a potential plume of escaped gas should be detected before it travels to within 3 × tREACT days travel time to the property boundary (POE) adjacent to the nearest receptor. At MVLF, 3 × tREACT = 30 days (i.e., one month). Therefore, because TOTWELL-REC is two months the CM frequency cannot be longer than one month (i.e., 2 minus 1) if CM will be performed at GP01. Establish Confirmation Monitoring Duration: The duration of CM based on the maximum TOT to probe GP01 is 1.75 years (i.e., 21 months). 5.7.3

Completion of Confirmation Monitoring

Based on the above, gas CM should be performed monthly at perimeter probe GP01 for a period of 21 months. While gas CM is ongoing, monitoring of potential gas impacts (i.e., selected VOCs) to groundwater should also be continued at MW-14 in accordance with the groundwater monitoring program. In the context of this CM program at MVLF, it is assumed that monthly CM would have been initiated in July 2002, at the time that NYSDEC approved transition to passive gas venting. This means CM would have been scheduled to be completed in April 2004. Monitoring data records at MVLF show no gas impacts were detected at perimeter probes or groundwater wells during this period; therefore, by April 2004 the Gas Module evaluation would have demonstrated that eliminating active LFG controls and converting to a fully passive venting system is an acceptable and sustainable long-term method of LFG management.


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6.

FUNCTIONAL STABILITY WITH RESPECT TO LEACHATE

6.1


6.1.1

Background

Demonstrating that leachate is not a potential threat to HHE is a primary driver for functional stability through the process of optimization and elimination of active leachate management. Where it is necessary to continue active management of leachate in the medium or long term, evaluations in the EPCC Leachate Module facilitate decision-making on how this can be done in a more effective, low maintenance, or self-regulating way. Examples include using constructed wetlands or natural biofilters for onsite treatment with direct discharge rather than simply transporting untreated leachate to a wastewater treatment plant (WWTP) for disposal. Potential threats to HHE posed by a leachate release are evaluated using a step-up approach based on: •

The existence of adequate monitoring data collected over a sufficient period of time to confidently characterize the leachate source relative to regulated parameters in groundwater and surface water;

•

A demonstration that the historical concentration trend for selected “gateway” parameter(s) is decreasing or steady;

•

A proposed strategy for long-term, preferably passive, leachate management; and

•

Demonstration of the acceptability of the proposed long-term leachate management strategy based on the absence of threat to HHE at the source, groundwater and/or surface water POC, or point of exposure (POE), which is generally the property boundary or nearby receptor such as a river or lake, and should be clearly defined at the time of the evaluation.

Passing an evaluation for all regulated parameters allows implementation of the new leachate management strategy as proposed, subject to successful navigation through a series of confirmation monitoring processes that provide a check on the evaluations. 6.1.2

Procedural Basis

Due to ongoing updates to EPCC since initial publication in 2006, the systematic procedures for application of the Leachate Module are currently provided in two separate technical reference sources. 1. EPCC Methodology Technical Manual (Appendix E of EREF, 2006)


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Data requirements and other prerequisites are described in Sections 3.3 and 3.5 of the document while detailed procedures for data evaluation are provided in Section 4 and Appendices E-1 and E-2. 2. EPCC Methodology Prerequisites Study (EREF, 2011) In the follow-up study performed for EREF by Geosyntec between 2007 and 2009, data collection requirements and prerequisites for the Leachate Module were simplified and updated. Details are provided in Section 7 and Appendices 1-3 and 1-4 of the document. 6.2

Site Features of Relevance to the Leachate Module

Site features of relevance to the Gas Module include: •

Physiographic setting and distance to POC and/or nearest potential receptor(s) at the POE

•

Liner system (base grades) and leachate collection system (LCS)

•

Leachate management system, which at MVLF includes the groundwater suppression system (GSS)

•

Final cover system and stormwater management system

•

Site geology and hydrogeology

•

Leachate, groundwater, and surface water monitoring system

Details are provided in Section 2. In addition, the assumed end use condition of the landfill property (Section 4) is important. 6.3

Prerequisites

The prerequisites for performing an evaluation in the Leachate Module are reviewed below. It is assumed that 1992 represents year zero for PCC at MVLF as waste placement ceased in 1991. Therefore, meeting of prerequisite conditions is assessed relative to this date. 6.3.1

Leachate Management and Monitoring Systems in Place

The primary prerequisites for performing a leachate evaluation are elementary: there should be a leachate management system in place that, at least in part, requires some active operation and maintenance. Evaluating modification or termination of active leachate management cannot be performed where these do not exist. In addition, there should be the ability to measure leachate quality and flow, and a water quality monitoring network in place to measure environmental performance.


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The leachate management system at MVLF can be broken down into three distinct components: •

Leachate Collection System (LCS): MVLF is a pre-Subtitle D landfill that lacks a composite geomembrane liner system and traditional basal LCS. Leachate is collected above the low permeability natural gray till that serves as the de facto liner. Base grades slope downward to the northeast, directing leachate to a passive leachate collection system consisting of a perimeter leachate collection pipe around the east, north, and west downslope toes of the landfill.

•

Leachate Transmission and Storage: The LCS drains by gravity toward two leachate storage tanks designated as East Tank (ETANK) and West Tank (WTANK). In addition, a passive groundwater suppression system intercepts groundwater from the eastern downgradient side of the landfill, which gravity flows to two tanks designated as D01.

•

Leachate Treatment System: In 2012, a constructed wetlands treatment system (CWTS) was designed and installed for onsite treatment of liquids from ETANK, WTANK, and D01 and permitted discharge of treated effluent to the Mohawk River.

Figure 6-1: Site Features of Relevance to the Leachate Module


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The layout and components of the leachate management system are illustrated on Figure 6-1. An extensive water quality monitoring network exists at the site, with environmental data collected in accordance with the EMP (Section 2.3). As will be discussed subsequently, the groundwater monitoring wells and surface water outfalls shown on Figure 6-1 are the primary locations that will be used to assess potential impacts from leachate. 6.3.2

Leachate Management Strategy

To avoid issues with leachate accumulation within the landfill, Geosyntec assumed that leachate will continue to be drained passively from the landfill. However, the current mechanism for onsite storage of leachate in tanks prior to offsite trucking for WWTP disposal will be replaced with full onsite management using the CWTS. In addition, under the proposed end use strategy (Section 4), it is assumed that maintenance of the existing clay cap and stormwater management system will continue. This allows evaluation of the Leachate Module to focus on optimization or elimination of groundwater and/or surface water monitoring based on a demonstration that leachate does not represent a threat to water quality. 6.3.3

Historical and Current Leachate Impacts

To proceed with an evaluation, a second prerequisite is that there should be no current compliance issues related to leachate releases or impacts at the landfill. Based on site reports, there have been no such issues since improvements were made to the LCS in the early 1990s. Review of analytical groundwater data indicates that water quality in and around the landfill site is generally consistent with regional water quality and that water quality in downgradient wells is comparable to upgradient wells. Similarly, surface water monitoring data in and around the landfill site are generally very good. 6.3.4

Leachate Data and Sampling Locations

As a general prerequisite, the groundwater and surface water parameters monitored under the EMP must also be available in source leachate, with sufficient data available to allow statistical analyses to be performed. A minimum of eight data points is required for the leachate source designated as the primary source, with at least one corresponding data point required for each secondary source. The primary source is typically a central storage tank or master sump from which a composite sample is taken for analysis, whereas secondary sources are individual cell sumps; however, that is not the case at MVLF as no true sumps exist. For this reason, ETANK is assigned as the primary source (“composite”) and WTANK as the secondary source (“sump”) because leachate is routed to ETANK from a larger proportion of the LCS than to WTANK and thus a leachate quality in this tank is representative of a larger area of the landfill. Leachate data availability for both tanks is generally good, with quarterly collection of leachate samples having been conducted since the late 1980s or early 1990s. Prior to 2012, monitoring of a total of 62 groundwater and 63 surface water analytes was required under the EMP (the analyte lists were identical with the exception of dissolved oxygen ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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being required in surface water). However, the number of surface water analytes monitored following construction of the CWTS in 2011 decreased to 42, reflecting more focused monitoring under the SPDES Permit. Significant overlap remains between the groundwater and surface water analyte lists. 6.3.5

Water Quality Standards and Guidelines

Federal, State, and/or site-specific water quality standards and guidance (WQSG) enforced at the site govern evaluation of potential leachate impacts. Often, WQSG limit values are made increasingly more stringent with time (e.g., as evidence emerges of ecological or human health concerns at lower concentrations of contaminants in the environment, or improvements in laboratory analytical techniques result in lower reporting limits). As a result, some WQSG limit values applicable at MVLF may have decreased over time and this should be reflected in the analysis since a retroactive series of evaluations will be made. However, for ease of crosscomparison between results and to remain conservative in the analysis, in this study the most recently published limit values were applied to all evaluations. On occasion, more than one limit value is specified within a particular WQSG, in which case the most stringent value corresponding to use of surface water or groundwater as a source of drinking water is applied. The order of potential applicability of WQSG at MVLF is ranked as follows. Following this approach, comparison is made to a limit value for a regulated parameter from a lower-ranked WQSG only if a limit value in not available under a higher ranked WQSG 4. •

Groundwater: 1. Groundwater effluent limitations for discharges to Class GA water contained in New York State Regulation 6NYCRR Part 703.6 or ambient water quality standards contained in 6NYCRR Part 703.3 through 703.5 5; 2. Guidance values contained in NYSDEC Division of Water Technical and Operational Guidance Series (TOGS) 1.1.1 (ambient values) and 1.1.2 (groundwater effluent limitations), dated June 1998 6; 3. Federal drinking water maximum contaminant level (MCL) per the National Primary Drinking Water Regulations (40CFR Part 141) 7;

4

It is stressed here that comparison to lower-ranked WQSG for either groundwater or surface water was not required at MVLF because higher-ranked WQSG were available to provide limit values for all regulated parameters. The above lists are provided for completeness only and to offer the reader some guidance on ranking potential sources of limit values that could be used in an analysis in the event that specific standards are not available.

5

http://www.dec.ny.gov/regs/2485.html

6

http://www.dec.ny.gov/docs/water_pdf/togs111.pdf

7

http://www.ecfr.gov/cgi-bin/text-idx?tpl=/ecfrbrowse/Title40/40cfr141_main_02.tpl


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4. The USEPA’s most recently published Regional Screening Level (RSL) for residential tap water 8; 5. Background groundwater quality based on a calculated 95% upper prediction limit (UPL) using data from upgradient well MW-6 9; or 6. The current reporting limit (RL) 10 for an analyte provided by the laboratory that conducts routine analyses of leachate samples from the landfill. •

Surface water: o Monthly maximum, daily maximum, or Type I monitoring limit from SPDES Permit No. #NY0257150 (applicable in the order listed following installation of the onsite CWTS only); o Effluent limitations or standards contained in 6NYCRR Part 703.6 or Part 703.35, respectively; o Guidance values contained in TOGS 1.1.1 or 1.1.2; o Federal maximum monthly average limit values for surface water discharges under 40CFR Part 445, Subpart B 11; o Federal drinking water MCL; o Federal RSL; o Background surface water quality based on a calculated 95% upper prediction limit (UPL) based on upgradient surface water samples; or o The laboratory RL.

6.3.5

Groundwater Indicator Parameter

The EPCC leachate evaluation requires selection of an appropriate (i.e., conservative, unattenuated) indicator parameter for confirmation monitoring. These fast moving, non-retarded chemicals can be used to define the leading edge of a potential leachate plume. Detection of the indicator parameter at a POC well at a concentration equal to or greater than a specified “trigger 8

http://www.epa.gov/risk/risk-based-screening-table-generic-tables

9

Use of a 95% UPL to establish the background mean for groundwater samples from one or more upgradient wells and similar statistical methods to help make environmental impact decisions is common (e.g., USEPA, 1988; Sara, 2003).

10

Note that assigning the limit value as the RL is very conservative given that laboratory methods continually improve (i.e., the current RL should be lower than that achievable during past analyses). By definition, any analyte requiring comparison to the RL cannot pass unless: (1) all data are reported ND from undiluted samples (in which case a concentration of zero may be assigned); or (2) a dilution attenuation factor (DAF) is applied for comparison at the POC or POE.

11

https://www.gpo.gov/fdsys/granule/CFR-2007-title40-vol29/CFR-2007-title40-vol29-part445


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concentration” (addressed later) would be an indication that leachate-related impacts might be present in groundwater moving toward the POC and would allow appropriate action to be taken well in advance of migration of slow-moving, attenuated parameters reaching the POC. The Technical Manual discusses selection of chloride, sulfate, or ammonia-N as the primary indicators for which clear order of magnitude concentration differences typically exist between source leachate and background water quality. Wehran (1991) reports that upgradient groundwater data in monitoring well couplets MW-6 and MW-7 at MVLF is characterized by low chloride concentrations, making this the ideal indicator parameter (i.e., elevated chloride concentrations detected in downgradient monitoring wells can be confidently attributed to leachate). 6.4

First Leachate Module Evaluation L1-Y5 (1997)

Completing an evaluation within five years of entering PCC should provide a useful “first look” at how the site is performing and whether sufficient data are being collected. This helps set expectations and make informed decisions about the timing and potential scope of future modifications that will be possible. Entering this evaluation with the perspective of an “EPCC Consultant” with the information available in 1997, it is anticipated that Evaluation L1-Y5 would serve primarily to suggest when the next follow up evaluation should be scheduled. Raw data, input assumptions, and detailed results from Evaluation L1-Y5 are provided in Appendix 3. A summary of pertinent findings is provided in the remainder of this section. 6.4.1

“Gateway” Indicators of Functional Stability

For this initial evaluation, attention is focused on two primary indicators of leachate quality: (1) biochemical oxygen demand (BOD); and (2) the ratio of BOD to chemical oxygen demand (COD). Research (e.g., Bookter and Ham, 1982; Shimaoka et al., 1993) has indicated that as the waste in a landfill degrades, the bottom-most MSW layers become well decomposed (as measured by BOD concentration in leachate collected in a basal LCS) and act as a biofilter with a large attenuating capacity for degradable organics and heavy metals. Building on this, other researchers (e.g., Gibbons et al., 2014) have demonstrated a significantly decreasing trend in BOD concentration as a suitable surrogate for trends in other constituents of concern in leachate, including heavy metals and VOCs, unless landfill redox conditions are allowed to change significantly (e.g., as a result of massive cover degradation leading to significant air intrusion through the entire waste mass, which is highly unlikely). Other studies (e.g., Kjeldsen et al., 2002; Barlaz et al., 2002) have suggested that an absolute BOD concentration less than 100 mg/L and a BOD/COD ratio less than 0.1 are representative of leachate from relatively well-degraded waste. Although these are insufficient conditions in themselves for concluding biochemical stability, they are strong indicators that a landfill is trending toward waste stabilization. Accordingly, a statistically significant decreasing trend in BOD below a threshold value of 100 mg/L and an absolute BOD/COD ratio below 0.1 are used in this evaluation as “gateway” indicators of the onset of functional stability conditions in leachate. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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BOD Trend: In this first step, a statistical demonstration that the historical concentration trend for BOD is decreasing or steady is made, such that there is a high level of confidence that leachate quality will not worsen in the future. This validates subsequent evaluation of future “no threat” predictions based on current leachate quality. BOD data from 28 sampling events at ETANK and WTANK were available at MVLF for the period January 1990 to July 1997, representing both pre- and post-closure conditions. Both datasets exhibit a lognormal distribution with no outliers. A downward trend based on a best fit exponential trend line is evident (Figure 6-2).

Figure 6-2: Evaluation L1-Y5, Leachate BOD Concentration Trend

The data are more closely correlated for ETANK (R2 = 0.57) than for WTANK (R2 = 0.41). The exponential trend lines on the figure (note log scale) suggest that BOD concentrations should be expected to routinely meet the quality threshold value of 100 mg/L around 1997 for ETANK and 1995 for WTANK. Statistical down trends in the data were confirmed using the more robust Sen’s test 12. This trend behavior means that deeper evaluation of regulated parameters should be conducted (Section 6.4.2) because leachate analytes that are below standards in 1997 will likely remain below the standard in the future. BOD Concentration: The current BOD concentration was calculated as the 95% UCL to the mean of the data 13. This statistically representative BOD concentration in 1997 (i.e., year 5 of PCC) is 165.6 mg/L in ETANK and 39.1 mg/L in WTANK, the latter being suggestive of highly stable leachate. As such, BOD concentrations in ETANK do not yet meet this gateway criterion 12 Sen’s test is a simple nonparametric estimator of trend which is robust to outliers, missing data, and non-detects and provides both an estimate of the rate of change and a test of the null hypothesis of no trend (Sen, 1968). 13 Use of a 95% UCL in this way means there is 95% confidence that the true concentration of the next BOD sample collected will be lower than this value.


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for the onset of functional stability, although the trending data suggest it could be met soon. This means it should be expected that further evaluation (Section 6.4.2) using 1997 data will show that the current leachate management and monitoring systems cannot be discontinued. The disparity in leachate quality between the two tanks may be due to the fact that the portion of the LCS draining to WTANK covers only a small area of the landfill and may collect leachate from relatively older waste filling operations. This finding supports use of ETANK as the primary leachate source (or “composite”) and WTANK as the secondary source (i.e., ETANK provides a conservative measure of overall leachate quality). BOD/COD Ratio: Concurrent composite BOD and COD data were available from 28 sampling events for the period January 1990 to July 1997. Overall, the data shown in Figure 6-3 (note log scale) suggest that the BOD/COD stability criterion was not routinely met at the landfill prior to 1997. Only six and nine samples from ETANK and WTANK, respectively, exhibited a BOD/COD less than 0.1. As such, leachate does not yet meet this gateway criterion for the onset of functional stability and, again, it should be expected that further evaluation will show that the current leachate management and monitoring systems cannot yet be discontinued. However, a broadly decreasing trend in the BOD/COD ratio is evident, particularly in ETANK, which is a positive finding.

Figure 6-3: Evaluation L1-Y5, Ratio of BOD/COD Concentrations in Leachate

6.4.2

Evaluation of Potential Threat posed to Human Health and the Environment

The previous step provides a high level of statistical confidence that leachate quality will continue to improve with time due to the high state of organic degradation evident in key indicators. Building on this, this step evaluates potential threats posed by leachate to HHE. If statistically valid current leachate concentrations for analytes of concern are used, and the evaluation indicates that no threat to HHE will occur, then there is no reason to expect that future ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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leachate concentrations will be problematic. Note that EPCC’s definition is that a closed landfill is functionally stable when it does not present a threat to HHE at the POE, with the POE identified as the closest location at which a receptor could be exposed to contaminants and receive a dose by a credible pathway from the landfill. Pathways for Leachate Migration and Impacts: Potential impacts are measured at the POC, located between the landfill source and the POE. Based on this, a conservative estimate of potential impact from leachate at MVLF is based on the following: •

Groundwater: Leakage of leachate into the subsurface through the base of the landfill and direct migration to groundwater (GW). The GW POC is assigned as deep well MW11C, which is screened in bedrock (Utica Shale, the uppermost aquifer).

•

Surface Water (Indirect): Leakage of leachate into the subsurface through the base of the landfill and indirect migration via the superficial alluvium/brown till, which are hydraulically connected to surface water (SW) in the Mohawk River (see Figures 2-2 and 2-3). The SW POC is established as shallow well MW-11B, which is screened in the alluvium/brown till.

•

Surface Water (Direct): Direct seepage and runoff of leachate to an onsite stormwater pond, with the SW POC defined as Outfalls 002 and 003.

Locations of wells and outfalls are shown on Figure 6-1. To demonstrate no threat to HHE under these assumptions, water quality must be shown to remain in compliance with protection standards at the POC. Data Processing: Leachate data from ETANK (the primary source) were initially processed to address censored data (essentially, assigning a statistically representative value for non-detect parameters, which is not necessarily zero), test for and remove outliers, test for distributional form (i.e., normal, log-normal, non-parametric, or no distribution), and adjust for trends as necessary. This enabled a statistically representative current concentration for each regulated analyte in GW and SW to be computed 14. The water quality protection standards are all applied as categorical limits; therefore, a 95% upper confidence limit (UCL) was computed for each analyte to compare to the standard 15. Because laboratory techniques (and, in particular, dilutions

14

For this study, Geosyntec tailored a Microsoft Excel® spreadsheet tool to perform the analyses described in this section. Therefore, while not exactly representing an “off the shelf” tool, performing the data analyses required in the Leachate Module should not represent an undue burden for a well-qualified engineer, geologist, or environmental scientist. It is noted that commercially available tools such as DUMPStat® (see www.discerningsystems.com) or LandSim® (see www.landsim.com) may utilized for this purpose. 15

If comparison is to a categorical limit rather than a statistical background value, then a 95% UCL is appropriate as discussed in USEPA (1988). At least four data points are required to compute a valid 95% UCL. Note that the 95% UCL is a conservative estimate of a current value based on historical data (in this case, concentration of an analyte) for which there is 95% certainty that the next future measurement will not exceed the computed value. The 95% UCL is therefore higher where there is more variability in the historical dataset. In this context, Geosyntec ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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used) in analysis of leachate samples were not known for older data collected at MVLF, the concentration of all qualified analytes (i.e., data reported as “less than”) and all data reported as “non-detect” (ND) were set to the reporting limit (RL) or detection limit (DL), respectively, a conservative measure in both regards. A 95% upper prediction limit (UPL) was also calculated to statistically compare consistency between ETANK and WTANK, such that the evaluation can move forward in a more straightforward manner using ETANK data only 16. Sufficient data were available for all but two analytes to compute a UCL value (see Tables 6-1 and 6-2) and UPL value. The analytes for which data were missing were total phenols (regulated in both GW and SW, but represented by phenol in the analysis) and dissolved oxygen (regulated in SW only). Data Consistency Testing: To be confident that the primary leachate source (ETANK) is truly representative of leachate collected across the entire basal area of the landfill, the Leachate Module requires “snapshot” consistency testing to be performed between the calculated 95% UPL for the primary source and the most recently collected single value from the secondary source (WTANK). With the exception of the two missing analytes (phenols and dissolved oxygen) which could not be tested, all data from WTANK were consistent with ETANK. Comparison to Groundwater Standards at the Landfill Source: Direct comparison of leachate quality to a water quality standard or guideline (WQSG) without consideration of potential dilution/attenuation effects between the landfill and POC is a quick and helpful way to understand which leachate constituents may pose a credible threat to water quality, because any parameter that passes such a comparison meets the limit value at the source and is, therefore, not of concern. Ignoring phenols, there are 51 parameters for which a WQSG limit value applies in groundwater at MVLF. Of these, 25 (49%) pass the source evaluation and 26 (51%) fail. Of the parameters that failed the evaluation, ammonia is the “worst case” requiring dilution by a factor of nearly 200 to meet its assigned limit value of 2 mg/L. Results are summarized in Table 6-1, with pH (a special case for which readings should remain between 6.5 and 8.5 rather than meet a categorical limit) presented in Figure 6-4.

computed the 95% UCL for both the four most recently collected samples and for the entire dataset for each analyte, and selected the lower value as being most appropriate as a conservative indictor of current concentration. 16

In brief, a 95% UPL is used to statistically compare consistency between primary and secondary leachate source concentrations. At least eight data points are required to compute a UPL. Although not directly pertinent to this study, it should be noted that a 95% UCL is used to compare a leachate constituent to a categorical limit value such as a drinking water standard; if the 95% UCL is below the limit value then there is 95% confidence that the true concentration is also below the limit. However, if background concentrations exceed the limit value for a particular analyte, or if there is no limit value, then the mean is instead compared to a 95% UPL for the background mean (e.g., groundwater samples from one or more upgradient wells). ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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Figure 6-4: Evaluation L1-Y5, Leachate pH

Comparison to Groundwater Standards at the POC: The first step in this comparison is calculation of a conservative dilution factor (DF) ignoring the effects of attenuation. If leachate leaks from the base of a landfill and enters the underlying aquifer, it will mix with groundwater traveling horizontally beneath the landfill and be diluted. In addition to the rate of leachate infiltration, this mixing of groundwater and leachate depends on several factors as outlined in Equation 6-1 below 17. The DF can be calculated from this equation as the ratio of horizontal flow (i.e., groundwater flow) to vertical flow (i.e., infiltration).

(Equation 6-1) Where: DF = dilution factor (dimensionless) K = aquifer hydraulic conductivity (feet/day) i = hydraulic gradient (feet/feet) w = width of the landfill perpendicular to the direction of groundwater flow (feet) d = thickness of the mixing zone (feet) 17

The U.S. EPA’s Multimedia Exposure Assessment Model (MULTIMED), a computer program developed as a tool for the study and design of Subtitle D land disposal facilities (Sharp-Hansen et al., 1990), or several other commercially available groundwater models could be used to simulate the transport and transformation of chemical constituents released from a waste disposal facility into the environment. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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I = infiltration rate (feet/day) Alandfill = landfill area over which infiltration occurs (ft2) The U.S. EPA’s HELP Model was used to estimate the expected liner leakage rate at MVLF. The resulting leakage rate was calculated as 1.8 ft3 per acre per day, which yields a total infiltration rate (I) from the 29-acre landfill to the aquifer of 4.13 × 10-5 feet/day. An aquifer hydraulic conductivity of 0.19 feet/day was assumed based on the hydraulic conductivity reported for the upper bedrock, downhill zone (see Table 2-1). The average groundwater gradient (i) beneath the landfill footprint was estimated at approximately 0.07 feet/feet, based on groundwater modeling performed by MMCE (2002b). The width of the landfill perpendicular to the direction of groundwater flow (w) is approximately 1,500 feet, measured from Figure 2 of MMCE (2002b). Although the aquifer beneath the landfill is estimated to be several hundred feet thick, a conservatively small mixing zone thickness of 15 feet was assumed for this analysis, which is equivalent to the longest screen length for deeper monitoring wells advanced into bedrock. Using these values, the DF for leachate migration to the GW POC well MW-11C was calculated to be 6.25 (see Appendix 3). Using this DF, of the 26 parameters failing the source evaluation, 12 (46%) pass the GW POC evaluation while 14 (54%) fail. Combining results from the source and POC evaluations, this means that from the total 51 regulated analytes tested, only 14 (28%) fail. This is a positive finding for a site only five years into post-closure. Results are summarized in Table 6-1.


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Table 6-1: Evaluation L1-Y5, Summary of Results from Leachate Evaluation (Groundwater) Analyte

Limit Value

Units

WQSG

Data Available

1,1-Dichloroethane 1,4-Dichlorobenzene 2-Butanone (MEK) 3-Methylphenol (m-cresol) 4-Methyl-2-pentanone (MIBK) 4-Methylphenol (p-cresol) Acetone Acetonitrile Acetophenone Aluminum Ammonia as N Antimony Arsenic Barium Benzene Beryllium Boron Cadmium Carbon disulfide Chloride Chromium, total Chromium hexavalent ion Color Copper Cyanide Diethyl phthalate Ethylbenzene Iron Isobutyl alcohol Lead Magnesium Manganese Mercury Methylene Chloride Naphthalene Nickel Nitrate pH Phenol Phenols Total dissolved solids (TDS) Selenium Silver Sodium Sulfate Thallium Toluene trans-1,2-Dichloroethene Trichloroethene Turbidity Xylenes, total Zinc

5 3 50 930 6300 1900 50 130 1900 2000 2 6 50 2000 1 3 2000 10 60 500 100 0.1 15 1000 0.4 50 5 600 5900 50 35 600 1.4 5 10 200 20 6.5-8.5 2 2 500 20 100 20,000 500 0.5 5 5 5 5 65 5000

ug/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L mg/L color units ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L

NY Part 703.5 NY Part 703.5 TOGS RSL RSL RSL TOGS RSL RSL NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 TOGS TOGS NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.6 RSL NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.5 NY Part 703.5 NY Part 703.3 TOGS NY Part 703.6

24 52 13 17 19 18 27 17 17 12 31 16 24 31 25 12 12 22 16 31 31 18 12 15 15 12 30 26 13 29 15 15 20 28 12 31 15 31 12 0 15 18 19 15 15 15 31 26 21 15 22 15

ug/L ug/L mg/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L NTU ug/L ug/L


60

95% UCL Pass at Source?

Required DF

Pass at POC?

4.66 TRUE 34.11 FALSE 11.37 FALSE 503.64 FALSE 10.07 FALSE 43.67 TRUE 571.12 TRUE 43.67 TRUE 434.89 FALSE 8.70 FALSE 127.61 TRUE 42.05 TRUE 321.78 TRUE 399.89 FALSE 199.95 FALSE 60.00 FALSE 10.00 FALSE 44.98 TRUE 1,565.21 TRUE 5.02 FALSE 5.02 TRUE 5.00 FALSE 1.67 TRUE 6,671.04 FALSE 3.34 TRUE 21.77 FALSE 2.18 TRUE 5.00 TRUE 1,329.27 FALSE 2.66 TRUE 57.69 TRUE 0.01 TRUE 1,107.39 FALSE 73.83 FALSE 111.26 TRUE 0.02 TRUE 10.00 TRUE 59.84 FALSE 11.97 FALSE 8,934.53 FALSE 14.89 FALSE 43.86 TRUE 19.92 TRUE 169.93 FALSE 4.86 TRUE 571.32 TRUE 0.20 TRUE 4.52 TRUE 34.22 FALSE 3.42 TRUE 204.57 FALSE 1.02 TRUE 0.26 TRUE Not appropriate statistical test for pH (see Figure 6-4) 21.64 FALSE 10.82 FALSE Represented by phenol 3,935.56 FALSE 7.87 FALSE 21.77 FALSE 1.09 TRUE 108.58 FALSE 1.09 TRUE 867,020.13 FALSE 75.49 FALSE 152.73 TRUE 28.87 FALSE 57.74 FALSE 72.40 FALSE 14.48 FALSE 8.55 FALSE 1.71 TRUE 4.52 TRUE 108.46 FALSE 21.69 FALSE 180.02 FALSE 2.77 TRUE 91.92 TRUE

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Comparison to Surface Water Standards at the Landfill Source: Direct comparison of leachate quality to WQSG limit values for SW at the site was conducted similar to the GW source evaluation. Results are summarized in Table 6-2. Ignoring phenols, there are 53 parameters for which a WQSG limit value applies in SW at MVLF. Of these, 24 (45%) pass the source evaluation, 28 (53%) fail, while data are not available for one parameter (dissolved oxygen). For all parameters failing the source comparison, the table indicates the DF that would be required to meet the SW standard (i.e., the extent of treatment that would be required to meet SW discharge criteria). Of the parameters that failed the evaluation, ammonia is the “worst case” requiring dilution by a factor of nearly 200 to meet its assigned limit value of 2 mg/L. The median DF value for all failing parameters is 6.44. Comparison to Surface Water Standards at the POC: This step requires calculation of a conservative DF again using Equation 6-1, this time for groundwater migration to the SW POC (shallow monitoring well MW-11B). Input to the equation are generally identical to those used above, except that an aquifer hydraulic conductivity of 2.83 feet/day was assumed based on the hydraulic conductivity reported for “more permeable materials” in alluvium/brown till (see Table 2-1). A mixing zone thickness of only two feet was assumed for this analysis, based on the maximum thickness of low permeability lenses (i.e., materials classified as SC, GM, or GC under USCS). These assumptions are valid as leachate migration to SW via the subsurface would be expected to be in such high permeability “corridors.” Using these values, the DF for leachate migration to the SW POC well MW-11B was calculated to be 12.24 (see Appendix 3). Using this DF, of the 28 parameters that fail the source evaluation, 21 (75%) pass the SW POC evaluation while only seven (25%) fail. Overall, this means that only 14% parameters fail both evaluations, a positive finding. Results are summarized in Table 6-2.


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Table 6-2: Evaluation L1-Y5, Summary of Results from Leachate Evaluation (Surface Water) Analyte

Limit Value

Units

WQSG

Data Available

1,1-Dichloroethane 1,4-Dichlorobenzene 2-Butanone (MEK) 3-Methylphenol (m-cresol) 4-Methyl-2-pentanone (MIBK) 4-Methylphenol (p-cresol) Acetone Acetonitrile Acetophenone Aluminum Ammonia as N Antimony Arsenic Barium Benzene Beryllium Biochemical oxygen demand Boron Cadmium Carbon disulfide Chloride Chromium, total Chromium hexavalent ion Color Copper Cyanide Diethyl phthalate Ethylbenzene Iron Isobutyl alcohol Lead Magnesium Manganese Mercury Methylene Chloride Naphthalene Nickel Nitrate Dissolved oxygen pH Phenol Phenols Total dissolved solids (TDS) Selenium Silver Sodium Sulfate Thallium Toluene trans-1,2-Dichloroethene Trichloroethene Turbidity Xylenes, total Zinc

5 3 50 930 6300 14 50 130 1900 2000 2 6 50 2000 1 3 37 2000 10 60 500 100 0.1 15 1000 0.4 50 5 600 5900 50 35 600 1.4 5 10 200 20 4 (min) 6.5-8.5 2 2 500 20 100 20,000 500 0.5 5 5 5 5 65 5000

ug/L ug/L ug/L ug/L ug/L UG/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L MG/L ug/L ug/L ug/L mg/L ug/L mg/L color units ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L mg/L

NY Part 703.5 NY Part 703.5 TOGS RSL RSL EPA Part 445 TOGS RSL RSL NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 TOGS EPA Part 445 TOGS NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.6 RSL NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.5 NY Part 703.5 NY Part 703.3 TOGS NY Part 703.6

24 52 13 17 19 18 27 17 17 12 31 16 24 31 25 12 28 12 22 16 31 31 18 12 15 15 12 30 26 13 29 15 15 20 28 12 31 15 0 31 12 0 15 18 19 15 15 15 31 26 21 15 22 15



62

95% UCL Pass at Source? 4.66 34.11 503.64 43.67 571.12 43.67 434.89 127.61 42.05 321.78 399.89 60.00 44.98 1,565.21 5.02 5.00 165.61 6,671.04 21.77 5.00 1,329.27 57.69 0.01 1,107.39 111.26 0.02 10.00 59.84 8,934.53 43.86 19.92 169.93 571.32 0.20 4.52 34.22 204.57 0.26

TRUE FALSE FALSE TRUE TRUE FALSE FALSE TRUE TRUE TRUE FALSE FALSE TRUE TRUE FALSE FALSE FALSE FALSE FALSE TRUE FALSE TRUE TRUE FALSE TRUE TRUE TRUE FALSE FALSE TRUE TRUE FALSE TRUE TRUE TRUE FALSE FALSE TRUE

Required DF

Pass at POC?

11.37 10.07

TRUE TRUE

3.12 8.70

TRUE TRUE

199.95 10.00

FALSE TRUE

5.02 1.67 4.475833 3.34 2.18

TRUE TRUE TRUE TRUE TRUE

2.66

TRUE

73.83

FALSE

11.97 14.89

TRUE FALSE

4.86

TRUE

3.42 1.02

TRUE TRUE

Not appropriate statistical test for pH (see Figure 6-4) 21.64 FALSE 10.82 TRUE Represented by phenol 3,935.56 FALSE 7.87 TRUE 21.77 FALSE 1.09 TRUE 108.58 FALSE 1.09 TRUE 867,020.13 FALSE 43.35 FALSE 152.73 TRUE 28.87 FALSE 57.74 FALSE 72.40 FALSE 14.48 FALSE 8.55 FALSE 1.71 TRUE 4.52 TRUE 108.46 FALSE 21.69 FALSE 180.02 FALSE 2.77 TRUE 91.92 TRUE

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6.4.3


As indicated on Figures 6-2 and 6-3, a principal result from Evaluation L1-Y5 is that “gateway” criteria for functional stability have already been met or will likely be met soon. This is borne out in subsequent evaluations, which show that over half of all regulated GW and SW parameters already meet conditions for functional stability in leachate. However, no significant modification or scaling back of leachate control or monitoring is appropriate at this time, because 14 constituents in leachate could impact GW quality at the POC if unmanaged while 28 and seven constituents, respectively, could impact SW quality in the onsite ponds or at the POC for indirect migration to the river. Based on this, and again from the perspective of the EPCC Consultant in 1997, it would likely be recommended that a follow-up evaluation should be performed no later than 2007. 6.5

Second Leachate Module Evaluation L2-Y10 (2002)

By 2000, ongoing operation and monitoring of the LFG system and LFGTE plant showed that WMNY was experiencing difficulties in operating the LFGTE plant. In 2001, WMNY submitted notification to NYSDEC that they could no longer effectively operate the plant and that they would begin to evaluate the feasibility of passive alternatives or eliminating LFG management. As discussed in Section 5.5, it is assumed that WMNY would have responded to this situation by retaining the EPCC Consultant to evaluate the feasibility of alternative LFG controls (Gas Module Evaluation G2-Y9). It is assumed that finding from Evaluation G2-Y9 (i.e., rapid reduction in LFG generation with its implications for accelerated waste stabilization) would also have triggered reevaluation of the Leachate Module. This is supported by WMNY’s intensive solids sampling and analysis program conducted during the 2001-2002 timeframe (Section 3). Reports prepared for this program also provide a description of site conditions relevant to leachate management at the time, which is helpful for this study. In the context of this retroactive study, therefore, it is assumed that WMNY would have responded to the above situation by retaining the EPCC Consultant to reevaluate the Leachate Module in August 2002, exactly five years after the initial evaluation and five years ahead of the anticipated schedule. This second Leachate Module evaluation, occurring in 2002 in Year 10 of PCC, will be denoted as Evaluation L2-Y10. Raw data, input assumptions, and detailed results from this evaluation are provided in Appendix 3. A summary of pertinent findings is provided in the remainder of this section. Unless explicitly stated herein, the basis of evaluations remains consistent with the explanations provided for Evaluation L1-Y5 in Section 6.4. 6.5.1


BOD Trend: BOD data from 48 sampling events at ETANK and WTANK were available at MVLF for the period January 1990 to July 2002. The ETANK dataset exhibits a lognormal distribution with one outlier (shown orange on Figure 6-5a). The WTANK dataset exhibits a nonparametric distribution with no outliners (Figure 6-5b). A well correlated downward trend based on a best fit exponential trend line is evident for both datasets. The exponential trend lines ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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on the figure (note log scale) are consistent with findings from Evaluation L1-Y5 and suggest that BOD concentrations have routinely met the BOD quality threshold value of 100 mg/L since 1997 for ETANK and 1995 for WTANK. Statistical down trends in the data were confirmed using Sen’s test.


BOD Concentration: The current BOD concentration was calculated as the 95% UCL to the mean of the data as 35.1 mg/L in ETANK and 80.7 mg/L in WTANK. Examination of the two datasets indicates that BOD concentrations have not exceeded the threshold value of 100 mg/L since January 2000 (ETANK) or April 1996 (WTANK). The higher 95% UCL for WTANK is a result of the higher variability in that dataset relative to ETANK, which illustrates the inherent conservatism in using a 95% UCL to represent leachate concentrations. Nevertheless, both datasets are indicative of highly stable leachate. As such, BOD concentrations meet this gateway criterion for the onset of functional stability, which suggests that further evaluation (Section 6.5.2) will show progress towards functional stability with respect to leachate. BOD/COD Ratio: Concurrent composite BOD and COD data were available from 48 sampling events for the period January 1990 to July 2002. The data presented in Figure 6-6a (note log scale) shown that the stability criterion of BOD/COD less than 0.1 has been routinely met in ETANK since April 2000 (only three of 26 values have exceeded 0.1 since October 1995). Again, this is indicative of highly stable leachate. This stability criterion is not yet routinely evident in WTANK (Figure 6-6b) although 12 of 26 values since October 1995 were below 0.1 and only five exceeded 0.2. This suggests development of stable BOD/COD conditions are slightly lagging in WTANK relative to ETANK, but not by much. Absolute concentrations of BOD and COD in WTANK are also consistent with the 95% UPL to the mean of the data in ETANK.


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6.5.2


As in Evaluation L1-Y5, potential leachate impacts to groundwater (GW) and surface water (SW) are measured at a POC location between the landfill source and the POE. To demonstrate no threat to HHE under these assumptions, water quality must be shown to remain in compliance with protection standards at the POC. Pathways for Leachate Migration and Impacts: Conditions at the landfill are unchanged since the previous evaluation; therefore, potential leachate migration pathways and selection of GW and SW POC locations remain as previously described in Section 6.4.2. Locations of POC wells and outfalls are shown on Figure 6-1. Data Processing: Leachate data from ETANK were processed to address censored data and account for outliers, distributional form, and trend. This enabled a statistically representative current concentration for each regulated analyte in GW and SW to be computed. The water quality protection standards are all applied as categorical limits; therefore, a 95% UCL was computed for each analyte to compare to the standard. A 95% UPL was also calculated to statistically compare consistency between ETANK and WTANK, such that the evaluation can be conducted using ETANK data only. Sufficient data were available for all but two analytes to compute a UCL value (Tables 6-3 and 6-4) and UPL value. The analytes for which data were missing were total phenols (regulated in both GW and SW, but represented by phenol in the analysis) and dissolved oxygen (regulated in SW only). Data Consistency Testing: With the exception of the two missing analytes (phenols and dissolved oxygen) which could not be tested, all data from WTANK were consistent with ETANK. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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Comparison to Groundwater Standards at the Landfill Source: This step consists of direct comparison of source leachate quality to a water quality standard or guideline (WQSG) without consideration of potential dilution/attenuation effects. Ignoring phenols, there are 51 parameters for which a WQSG limit value applies in groundwater at MVLF. Of these, 31 (61%) pass the source evaluation and 20 (39%) fail. This represents a meaningful improvement over the even pass/fail split in 1997. Ignoring turbidity (a relatively unimportant parameter in the broader context of this evaluation), ammonia is the “worst case” of the analytes that failed the evaluation, requiring dilution by a factor of about 100 to meet its assigned limit value of 2 mg/L. Again, this is a significant improvement over the required DF of 200 in 1997. Results are summarized in Table 6-3, with pH (a special case for which readings should remain between 6.5 and 8.5) presented in Figure 6-7.


Comparison to Groundwater Standards at the POC: The conservative DF of 6.25 calculated using Equation 6-1 in Section 6.4.2 remains valid for this evaluation. Using this DF, of the 20 parameters failing the source evaluation, 9 (45%) pass the GW POC evaluation while 11 (55%) fail. Combining results from the source and POC evaluations, this means that from the total 51 regulated analytes tested, only 11 (22%) fail. This is a slight overall improvement over results in 1997. Results are summarized in Table 6-3.


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Limit Value

Units

WQSG

Data Available

1,1-Dichloroethane 1,4-Dichlorobenzene 2-Butanone (MEK) 3-Methylphenol (m-cresol) 4-Methyl-2-pentanone (MIBK) 4-Methylphenol (p-cresol) Acetone Acetonitrile Acetophenone Aluminum Ammonia as N Antimony Arsenic Barium Benzene Beryllium Boron Cadmium Carbon disulfide Chloride Chromium, total Chromium hexavalent ion Color Copper Cyanide Diethyl phthalate Ethylbenzene Iron Isobutyl alcohol Lead Magnesium Manganese Mercury Methylene Chloride Naphthalene Nickel Nitrate pH Phenol Phenols Total dissolved solids (TDS) Selenium Silver Sodium Sulfate Thallium Toluene trans-1,2-Dichloroethene Trichloroethene Turbidity Xylenes, total Zinc

5 3 50 930 6300 1900 50 130 1900 2000 2 6 50 2000 1 3 2000 10 60 500 100 0.1 15 1000 0.4 50 5 600 5900 50 35 600 1.4 5 10 200 20 6.5-8.5 2 2 500 20 100 20,000 500 0.5 5 5 5 5 65 5000



25 53 14 18 20 19 28 18 18 12 51 17 44 51 26 13 12 42 17 51 51 37 12 35 35 13 31 46 14 49 35 35 40 29 13 51 35 51 13 0 35 38 39 35 35 16 32 27 22 34 23 35



67


Required DF

Pass at POC?

3.10 TRUE 29.45 FALSE 9.82 FALSE 434.50 FALSE 8.69 FALSE 106.00 TRUE 577.85 TRUE 106.00 TRUE 1,101.52 FALSE 22.03 FALSE 128.10 TRUE 54.90 TRUE 321.78 TRUE 201.32 FALSE 100.66 FALSE 60.00 FALSE 10.00 FALSE 0.02 TRUE 1.11 TRUE 3.78 FALSE 3.78 TRUE 6.68 FALSE 2.23 TRUE 6,671.04 FALSE 3.34 TRUE 0.01 TRUE 6.35 TRUE 803.03 FALSE 1.61 TRUE 0.01 TRUE 0.16 TRUE 1.59 1,107.39 FALSE 73.83 FALSE 0.04 TRUE 0.02 TRUE 10.00 TRUE 42.46 FALSE 8.49 FALSE 22.26 TRUE 57.17 TRUE 0.01 TRUE 147.00 FALSE 4.20 TRUE 1.49 TRUE 0.00 TRUE 2.34 TRUE 32.91 FALSE 3.29 TRUE 0.09 TRUE 0.48 TRUE Not appropriate statistical test for pH (see Figure 6-7) 44.94 FALSE 22.47 FALSE Represented by phenol 2,858.02 FALSE 5.72 TRUE 0.03 TRUE 0.03 TRUE 527.51 TRUE 281.92 TRUE 29.32 FALSE 58.64 FALSE 45.49 FALSE 9.10 FALSE 1.00 TRUE 2.34 TRUE 592.81 FALSE 118.56 FALSE 275.52 FALSE 4.24 TRUE 0.17 TRUE

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Comparison to Surface Water Standards at the Landfill Source: Direct comparison of leachate quality to WQSG limit values for SW at the site was conducted similar to the GW source evaluation. Results are summarized in Table 6-4. Ignoring phenols, there are 53 parameters for which a WQSG limit value applies in SW at MVLF. Of these, 31 (59%) pass the source evaluation, 21 (40%) fail, while data are not available for one parameter (dissolved oxygen). This is an improvement over the pass rate of 45% (24/53 parameters) in 1997. For all parameters failing the source comparison, the table indicates the DF that would be required to meet the SW standard (i.e., the extent of treatment that would be required to meet SW discharge criteria). The median DF value for all failing parameters is 8.59. Similar to the GW source evaluation, of the important parameters that failed the evaluation, ammonia is the “worst case” requiring dilution by a factor of about 100 to meet its assigned limit value of 2 mg/L. Comparison to Surface Water Standards at the POC: The conservative dilution factor (DF) of 12.24 calculated using Equation 6-1 in Section 6.4.2 remains valid for this evaluation. Using this DF, of the 21 parameters that failed the source evaluation, 15 (71%) pass the SW POC evaluation while only six (29%) fail. Overall, this means that only 12% of parameters fail both evaluations, a positive finding. This is essentially the same result as in 1997, when seven parameters failed the evaluation. The suites of contaminants that fail the evaluations are similar, but not identical, as indicated below (the values in parentheses indicate the DF required to meet the SW standard): •

2002: Acetone (22), ammonia-N (101), phenol (23), and thallium (59), as well as two non-analytical measures of water quality: color (74) and turbidity (119), although it is noted that no new color data were collected since August 1997; and

•

1997: Ammonia-N (200), iron (15), sodium (44), thallium (58), and toluene (15), as well as color (74) and turbidity (22).

These nine contaminants likely represent the group of most recalcitrant compounds that do not readily degrade under landfill conditions and for which long-term leachate treatment may be required in order to allow onsite discharge to a SW receiving system. Results are summarized in Table 6-4.


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Table 6-4: Evaluation L2-Y10, Summary of Results from Leachate Evaluation (Surface Water) Analyte

Limit Value

Units

WQSG

Data Available

1,1-Dichloroethane 1,4-Dichlorobenzene 2-Butanone (MEK) 3-Methylphenol (m-cresol) 4-Methyl-2-pentanone (MIBK) 4-Methylphenol (p-cresol) Acetone Acetonitrile Acetophenone Aluminum Ammonia as N Antimony Arsenic Barium Benzene Beryllium Biochemical oxygen demand Boron Cadmium Carbon disulfide Chloride Chromium, total Chromium hexavalent ion Color Copper Cyanide Diethyl phthalate Ethylbenzene Iron Isobutyl alcohol Lead Magnesium Manganese Mercury Methylene Chloride Naphthalene Nickel Nitrate Dissolved oxygen pH Phenol Phenols Total dissolved solids (TDS) Selenium Silver Sodium Sulfate Thallium Toluene trans-1,2-Dichloroethene Trichloroethene Turbidity Xylenes, total Zinc

5 3 50 930 6300 14 50 130 1900 2000 2 6 50 2000 1 3 37 2000 10 60 500 100 0.1 15 1000 0.4 50 5 600 5900 50 35 600 1.4 5 10 200 20 4 (min) 6.5-8.5 2 2 500 20 100 20,000 500 0.5 5 5 5 5 65 5000

ug/L ug/L ug/L ug/L ug/L UG/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L MG/L ug/L ug/L ug/L mg/L ug/L mg/L color units ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L mg/L

NY Part 703.5 NY Part 703.5 TOGS RSL RSL EPA Part 445 TOGS RSL RSL NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 NY Part 703.6 NY Part 703.5 TOGS EPA Part 445 TOGS NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.6 RSL NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.5 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.3 NY Part 703.6 NY Part 703.6 NY Part 703.5 NY Part 703.6 TOGS NY Part 703.5 NY Part 703.5 NY Part 703.5 NY Part 703.3 TOGS NY Part 703.6

25 53 14 18 20 19 28 18 18 12 51 17 44 51 26 13 48 12 42 17 51 51 37 12 35 35 13 31 46 14 49 35 35 40 29 13 51 35 0 51 13 0 35 38 39 35 35 16 32 27 22 34 23 35



69

95% UCL Pass at Source? 3.10 29.45 434.50 106.00 577.85 106.00 1,101.52 128.10 54.90 321.78 201.32 60.00 0.02 1.11 3.78 6.68 29.12 6,671.04 0.01 6.35 803.03 0.01 0.16 1,107.39 0.04 0.02 10.00 42.46 22.26 57.17 0.01 147.00 1.49 0.00 2.34 32.91 0.09 0.48

TRUE FALSE FALSE TRUE TRUE FALSE FALSE TRUE TRUE TRUE FALSE FALSE TRUE TRUE FALSE FALSE TRUE FALSE TRUE TRUE FALSE TRUE TRUE FALSE TRUE TRUE TRUE FALSE TRUE TRUE TRUE FALSE TRUE TRUE TRUE FALSE TRUE TRUE

Required DF

Pass at POC?

9.82 8.69

TRUE TRUE

7.57 22.03

TRUE FALSE

100.66 10.00

FALSE TRUE

3.78 2.23

TRUE TRUE

3.34

TRUE

1.61

TRUE

73.83

FALSE

8.49

TRUE

4.20

TRUE

3.29

TRUE

Not appropriate statistical test for pH (see Figure 6-7) 44.94 FALSE 22.47 FALSE Represented by phenol 2,858.02 FALSE 5.72 TRUE 0.03 TRUE 0.03 TRUE 527.51 TRUE 281.92 TRUE 29.32 FALSE 58.64 FALSE 45.49 FALSE 9.10 TRUE 1.00 TRUE 2.34 TRUE 592.81 FALSE 118.56 FALSE 275.52 FALSE 4.24 TRUE 0.17 TRUE

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6.5.3


Evaluation L2-Y10 confirms that “gateway” criteria for functional stability have already been met and that downward trends in concentrations for indicator parameters are evident. This is borne out in subsequent evaluations, which show that the majority of regulated GW and SW parameters already meet conditions for functional stability in leachate. Measuring impacts at the POC, only 11 (22%) and six (12%) of regulated parameters would potentially impact GW or SW quality at the POC, respectively. This represents meaningful improvement over conditions in 1997 and indicates that leachate quality continues to improve as biodegradation of waste in the landfill continues. However, leachate control and monitoring remains necessary at the site, because these constituents could potentially impact water quality if leachate were unmanaged. With regard to long-term leachate management and the plan to eventually abandon offsite trucking of leachate in favor of onsite treatment and discharge (Section 6.3.2), the comparison of source leachate to SW standards indicates that 21 of 53 regulated parameters (40%) would require treatment. The median DF that would be required to meet the SW standard (i.e., the extent of treatment that would be required to meet SW discharge criteria) is low at 8.59. A suite of nine contaminants represents the group of most recalcitrant compounds for which long-term leachate treatment will be likely be required, of which ammonia is the “worst case” requiring a reduction of its representative concentration of 201 mg/L by a factor of about 100 to meet its assigned limit value of 2 mg/L. This level of treatment is can be readily provided by a passive or semi-passive CWTS system. Because treatment is required to meet discharge standards, effluent quality monitoring will be required. Based on this, from the perspective of the EPCC Consultant in 2002, it would likely be recommended as an outcome from Evaluation L2-Y10 that WMNY continuing monitoring progress toward functional stability and consider permitting and installation of a CWTS for onsite leachate management within the next five to ten years. 6.6

Third Leachate Module Evaluation L3-Y19 (2011)

WMNY started investigating installation of a constructed wetland treatment system (CWTS) at the site around 2008, six years after completion of Evaluation L2-Y10. SPDES Permit #NY0257150, issued in December 2009, authorizes discharge of treated effluent from the CWTS to surface water (Figure 2-6). The CWTS was constructed in 2011 and operational in 2012. Components and operation of the CWTS are described in MMCE (2012). Based on the above, in the context of this retroactive study it is assumed that WMNY would have retaining the EPCC Consultant to reevaluate the Leachate Module in August 2011, nine years after the last evaluation, as part of the process for transitioning to semi-passive, low maintenance onsite leachate management using the CWTS. This third Leachate Module evaluation is thus denoted as Evaluation L3-Y19. Raw data, input assumptions, and detailed results from this evaluation are provided in Appendix 3. A summary of pertinent findings is


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provided in the remainder of this section. Unless explicitly stated herein, the basis of evaluations remains consistent with previous evaluations in Sections 6.4 and 6.5. 6.6.1


BOD Trend: BOD data from 79 sampling events at ETANK and WTANK were available at MVLF for the period January 1990 to April 2011. Both datasets exhibits a lognormal distribution with no outliers and a strongly correlated downward trend based on a best fit exponential trend lines (Figure 6-8, note log scale). Consistent with findings from Evaluation L2-Y10, BOD concentrations have routinely met the BOD quality threshold value of 100 mg/L since 1997 for ETANK and 1995 for WTANK. Statistical down trends in the data were confirmed using Sen’s test.


BOD Concentration: The representative current BOD concentration (95% UCL) is 17.9 mg/L in ETANK and 5.4 mg/L in WTANK. Examination of the two datasets in Figure 6-8 indicates that BOD concentrations have exceeded the threshold value of 100 mg/L only once since January 2000 (ETANK) and April 1996 (WTANK). Both values are very low, suggestive of mild leachate and high levels of biodegradation and stability of the waste mass. BOD/COD Ratio: Concurrent composite BOD and COD data were available from 78 sampling events for the period January 1990 to April 2011. The data presented in Figure 6-8a (note log scale) confirm findings from Evaluation L2-Y9 that the stability criterion (BOD/COD < 0.1) has been routinely met in ETANK since April 2000, again indicative of mild leachate. As with the previous evaluation, the WTANK data (Figure 6-8b) are more scattered, suggesting development of stable BOD/COD conditions is slightly lagging ETANK but that leachate in WTANK can nonetheless be characterized as mild. Absolute concentrations of BOD and COD in WTANK remain consistent with the 95% UPL calculated for ETANK. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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6.6.2


As in previous evaluations, potential leachate impacts to groundwater (GW) and surface water (SW) are measured at a POC location between the landfill source and the POE. To demonstrate no threat to HHE under these assumptions, water quality must be shown to remain in compliance with protection standards at the POC. Pathways for Leachate Migration and Impacts: Evaluation L3-Y19 is intended to represent site conditions following installation of the CWTS, which means that conditions at the landfill have changed since the previous evaluation. Although GW remains regulated as specified for previous evaluations, future discharges to SW will be subject primarily to limit values specified in SPDES Permit #NY0257150. Based on this, a conservative estimate of potential impacts from leachate at MVLF is based on the following: •

Groundwater: Leakage of leachate into the subsurface through the base of the landfill and direct migration to GW (the CWTS is located too close to the river to be of concern as a source of impacts to GW – leakage from the CWTS will manifest in SW). The GW POC is assigned as deep well MW-11C, which is screened in bedrock (Utica Shale, the uppermost aquifer).

•

Surface Water (Indirect): Leakage of untreated leachate into the subsurface through the base of the landfill or from the CWTS, with indirect migration via the superficial alluvium/brown till which are hydraulically connected to the river (see Figures 2-2 and 23). The SW POC is established as shallow well MW-11B for the landfill and shallow well MW-9A for the CWTS.

•

Surface Water (Direct): Two separate potential pathways exist:


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o Direct seepage of leachate through the landfill sideslopes and runoff to an onsite stormwater pond, with the SW POC defined as Outfalls 002 and 003; and o Treated effluent discharged from the CWTS, with the SW POC defined as Outfall 001. The locations of the CWTS, monitoring wells, and outfalls are shown on Figure 6-1. Data Processing and Consistency Testing (Groundwater Analytes): Leachate data from ETANK were processed to address censored data and account for outliers, distributional form, and trend. This enabled a statistically representative current concentration for each regulated analyte in GW to be computed. The water quality standards or guidelines (WQSGs) are all applied as categorical limits; therefore, a 95% UCL was computed for each analyte to compare to the limit value. A 95% UPL was also calculated to statistically compare consistency between ETANK and WTANK, such that the evaluation can move forward using ETANK data only. Sufficient data were available for all but one regulated GW analyte (phenols, which is represented by phenol in the analysis) to compute a 95% UCL value (see Table 6-5) and 95% UPL value. With the exception of phenols, which could not be tested, all data from WTANK were consistent with ETANK. Comparison to Groundwater Standards at the Landfill Source: This step consists of direct comparison of source leachate quality to the WQSG limit value without consideration of potential dilution/attenuation effects. Ignoring phenols, there are 51 parameters for which a WQSG limit value applies in groundwater at MVLF. Of these, 38 (74.5%) pass the source evaluation and 13 (25.5%) fail. This represents a meaningful improvement over the 61% pass rate in 2002. Ammonia is the “worst case” of the important analytes that fail the evaluation, requiring dilution by about 64 times to meet its assigned limit value of 2 mg/L. This represents a steady improvement over the required DF of 100 in 2002 and 200 in 1997. Results are summarized in Table 6-5, with pH (a special case for which readings should remain between 6.5 and 8.5) presented in Figure 6-10. Comparison to Groundwater Standards at the POC: The conservative DF of 6.25 calculated using Equation 6-1 in Section 6.4.2 remains valid for this evaluation. Using this DF, of the 13 parameters failing the source evaluation, only two (ammonia-N and color, the latter a relatively unimportant parameter in the broader context of this evaluation) fail the GW POC evaluation while 11 (85%) pass. Combining results from the source and POC evaluations, only two of 51 regulated GW analytes (4%) fail overall. This is a significant overall improvement over results in 2002. Results are summarized in Table 6-5.


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Limit Value

Units

WQSG

Data Available

1,1-Dichloroethane 1,4-Dichlorobenzene 2-Butanone (MEK) 3-Methylphenol (m-cresol) 4-Methyl-2-pentanone (MIBK) 4-Methylphenol (p-cresol) Acetone Acetonitrile Acetophenone Aluminum Ammonia as N Antimony Arsenic Barium Benzene Beryllium Boron Cadmium Carbon disulfide Chloride Chromium, total Chromium hexavalent ion Color Copper Cyanide Diethyl phthalate Ethylbenzene Iron Isobutyl alcohol Lead Magnesium Manganese Mercury Methylene Chloride Naphthalene Nickel Nitrate pH Phenol Phenols Total dissolved solids (TDS) Selenium Silver Sodium Sulfate Thallium Toluene trans-1,2-Dichloroethene Trichloroethene Turbidity (Lab) Xylenes, total Zinc

5 3 50 930 6300 1900 50 130 1900 2000 2 6 50 2000 1 3 2000 10 60 500 100 0.1 15 1000 0.4 50 5 600 5900 50 35 600 1.4 5 10 200 20 6.5-8.5 2 2 500 20 100 20,000 500 0.5 5 5 5 5 65 5000



28 56 17 20 23 21 31 21 20 12 83 20 68 84 29 16 19 66 20 83 75 58 12 59 56 15 34 79 17 73 68 68 61 33 15 81 67 84 15 0 68 62 63 68 67 19 35 30 25 23 26 57



74


Required DF

Pass at POC?

4.52 TRUE 11.86 FALSE 3.95 TRUE 23.44 TRUE 10.00 TRUE 10.03 TRUE 10.00 TRUE 32.52 TRUE 43.40 TRUE 10.00 TRUE 321.78 TRUE 128.87 FALSE 64.44 FALSE 0.01 TRUE 0.01 TRUE 1.03 TRUE 3.83 FALSE 3.83 TRUE 0.00 TRUE 1.21 TRUE 0.01 TRUE 4.77 TRUE 509.35 FALSE 1.02 TRUE 0.01 TRUE 0.03 TRUE 1,107.39 FALSE 73.83 FALSE 0.03 TRUE 0.02 TRUE 10.00 TRUE 25.42 FALSE 5.08 TRUE 4.26 TRUE 49.79 TRUE 0.01 TRUE 120.14 FALSE 3.43 TRUE 0.44 TRUE 0.00 TRUE 14.54 FALSE 2.91 TRUE 18.38 FALSE 1.84 TRUE 0.08 TRUE 1.17 TRUE Not appropriate statistical test for pH (see Figure 6-10) 10.00 FALSE 5.00 TRUE Represented by phenol 1,917.04 FALSE 3.83 TRUE 0.01 TRUE 0.03 TRUE 371.15 TRUE 266.01 TRUE 0.00 TRUE 3.01 TRUE 5.11 FALSE 1.02 TRUE 2.76 TRUE 26.83 FALSE 5.37 TRUE 23.38 TRUE 0.02 TRUE

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Data Processing and Consistency Testing (Surface Water Analytes): The analyte list from the SPDES Permit includes 42 parameters, many of which are distinct from those included in previous GW and SW evaluations. No data exist for two analytes (o-xylene and m&p-xylene); however, for this study these are replaced with the single measure of total xylenes for which data are available. This reduces the analyte list to 41. Leachate data from ETANK were processed to address censored data and account for outliers, distributional form, and trend. A 95% UPL was calculated to statistically compare consistency between ETANK and WTANK, such that the evaluation can move forward using ETANK data only. Fewer than eight data points were available for five analytes in ETANK, which is insufficient to calculate a 95% UPL and thus perform a true comparison to WTANK. However, inspection of these limited datasets reveals that concentrations are very similar between the two tanks. Of the 36 parameters with sufficient data for a true statistical comparison, all data were consistent between tanks. The WQSG apply as categorical limits; therefore, a 95% UCL was computed for each analyte to compare to the limit value. Insufficient data were available for two analytes (α-turpinol and aniline) to calculate a 95% UCL (at least four data are required). For these parameters, the single highest value measured in ETANK is substituted as the representative value (see Table 6-6). Comparison to Surface Water Standards at the Landfill Source: Direct comparison of leachate quality to limit values for SW at the site is conducted similar to the GW source evaluation. Results are summarized in Table 6-6, with pH (a special case for which readings should remain ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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between 6.0 and 9.0) presented in Figure 6-10. There are 41 parameters included in this evaluation, of which two (5%) have insufficient data to calculate a 95% UCL for comparison to a categorical standard. For both these parameters, a qualified pass is obtained by comparing the single highest measured value to the standard. Of the remaining parameters, 32 (78%) pass the source evaluation while only seven (17%) fail. This is a significant improvement over the 59% pass rate obtained in 2002. For all parameters failing the source comparison, the table indicates the DF that would be required to meet the SW standard (i.e., the extent of treatment that would be required to meet SW discharge criteria). The median DF value required for all failing parameters is 4.35. Similar to the GW source evaluation, of the parameters that failed the evaluation, ammonia is the “worst case,” although its statistically representative concentration of 129 mg/L requires dilution by a factor of only about 26 to meet its assigned limit value of 4.9 mg/L. Comparison to Surface Water Standards at the POC: The conservative DF of 12.24 calculated using Equation 6-1 in Section 6.4.2 remains valid for this evaluation, because indirect migration of untreated leachate to SW via the subsurface takes place via the same media and under identical conditions as assumed in previous evaluations despite the introduction of the CWTS. Using this DF, of the seven parameters that failed the source evaluation, only ammonia-N fails at the POC, putting the overall pass rate at 97% (Table 6-6).


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Table 6-6: Evaluation L3-Y19, Summary of Results from Leachate Evaluation (Surface Water) Analyte 1,1,1-Trichloroethane 1,1-Dichloroethane 1,4-Dichlorobenzene a-Terpinol Aluminum Ammonia as N Aniline Arsenic Barium Benzene Benzoic Acid Biochemical Oxygen Demand Bis(2-ethylhexyl) phthalate Boron Chlorobenzene Chromium, Total Cobalt Copper Cyanide Ethylbenzene Iron Lead Xylenes, Total Manganese Mercury Naphthalene Nickel Oil and Grease 4-Methylphenol (p-cresol) pH Phenol Pyridine Selenium Sulfide Thallium Toluene Total dissolved solids (TDS) Total suspended solids (TSS) Vanadium Zinc

Limit Value

Units

10 10 10 19 4000 4.9 15 540 4000 5 73 56 10 1800 10 460 60 200 0.1 5 4000 120 15 2000 0.03 22 350 15 15 6-9 29 25 70 1 500 5 500 27 100 300

ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L ug/L ug/L mg/L ug/L ug/L mg/L mg/L ug/L ug/L

WQSG (note 1)

Data Available

Daily Daily Daily Monthly Daily Monthly Monthly Monthly Daily Daily Monthly Monthly Daily Daily Daily Monthly Type I Type I Type I Daily Daily Type I TOGS Daily Daily Monthly Type I Daily Monthly Weekly Monthly Monthly Type I Type I Type I Daily NY Part 703.3 Monthly Daily Monthly

25 28 56 2 12 83 2 68 84 29 12 84 16 19 41 75 7 59 56 34 79 73 26 68 61 15 81 55 21 84 15 4 62 61 19 35 68 59 7 57

95% UCL Pass at Source? Required (note 2) (note 3) DF

Pass at POC?

3.01 TRUE TRUE TRUE 4.52 11.86 FALSE 1.19 10.00 TRUE* 321.78 TRUE FALSE 26.30 128.87 FALSE TRUE* 10.00 0.01 TRUE TRUE 1.03 TRUE 3.83 TRUE 50.00 TRUE 17.93 FALSE 4.35 TRUE 43.53 TRUE 1.21 TRUE 6.51 TRUE 0.01 TRUE 11.00 TRUE 0.03 TRUE 0.02 FALSE 5.08 TRUE 25.42 4.26 TRUE 0.01 TRUE 23.38 FALSE 1.56 TRUE 0.44 TRUE 0.00 TRUE 18.38 TRUE 0.08 TRUE 5.00 TRUE 10.00 TRUE Not appropriate statistical test for pH (see Figure 6-10) 10.00 TRUE TRUE 200.00 FALSE 8.00 TRUE 0.01 0.20 TRUE 0.00 TRUE TRUE 3.01 3.83 TRUE 1,917.04 FALSE 19.3420931 TRUE 5 TRUE 0.02 TRUE

Notes: (1) Monthly, weekly, daily, and Type I limit values are specified in SPDES Permit # NY0257150; (2) Values shown in italics are single maximum values, not a 95%UCL, which requires a minimum four data for computation; and (3) Values indicated with an asterisk (*) are not true statistical pass relative to a 95% UCL.

6.6.3

Evaluation of Leachate Production

To complete assessment of functional stability with respect to leachate management, it should be demonstrated that leachate production is also decreasing. This would provide very high levels of confidence in previous conclusions drawn, because the potential mass load (i.e., concentration × volume) in any future leachate release would be lower than the current mass load. Although no ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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leachate flow data were available to Geosyntec for this study, MMCE (2002b) reported leachate generation at about 3,100 gallons per day (gpd), roughly equivalent to the upgradient groundwater inflow they modeled using MODFLOW. This suggests that the cap is effective at limiting infiltration. The 2009 SPDES Permit specifies a flow limitation of 10,000 gpd for the CWTS. This suggests relatively stable conditions and low rates of residual leachate generation. 6.6.4


The principal findings from Evaluation L3-Y19 can be summarized as follows: Groundwater: Of the 51 regulated parameters tested, 38 (74.5%) pass the source evaluation and only two (ammonia and color, the latter a relatively unimportant parameter in the broader context of this evaluation) of the remaining 13 parameters would impact GW in the uppermost aquifer (Utica Shale bedrock) as a result of leakage of leachate through the base of the landfill and subsequent migration to GW POC well MW-11C. The overall pass rate for analytes in this evaluation is 96%. Ongoing control of leachate is necessary only to protect GW from potential ammonia impacts, as the current 95% UCL concentration of 129 mg/L is one order of magnitude higher than the non-impacting concentration of 12.5 mg/L (i.e., the limit value of 2 mg/L multiplied by the DF of 6.25). If it can be demonstrated that ammonia does not pose a risk to HHE at the current concentration (for example, due to attenuation effects or if migration to the uppermost aquifer is not a realistic proposition), then leachate would meet conditions for functional stability in consideration of GW impacts under the defined leachate management strategy at the site. Alternatively, functional stability in this regard is automatically achieved if ammonia concentrations in leachate fall below 12.5 mg/L. Surface Water (Indirect): Of the 41 regulated parameters, 34 (83%) pass the source evaluation and only one (ammonia) of the remaining seven parameters would impact SW if untreated leachate were to leak from the landfill or CWTS and migrate to the river via superficial alluvium/brown till deposits (as measured at the SW POC, which is shallow wells MW-11B and MW-9A, respectively). The overall pass rate for analytes in this evaluation is 98%. Ongoing control of leachate is necessary only to protect water quality at the SW POE (the river) from potential ammonia impacts. The current concentration is about twice the non-impacting concentration of 60 mg/L (i.e., 4.9 mg/L × 12.24). Again, if it can be demonstrated that ammonia does not pose a risk to HHE under this migration scenario, then leachate meets conditions for functional stability in this consideration under the defined leachate management strategy at the site. Alternatively, functional stability in this regard is automatically achieved if ammonia concentrations in leachate fall below 60 mg/L. Surface Water (Direct): Two separate potential pathways exist (direct seepage and runoff of source leachate to an onsite stormwater pond, with the SW POC defined as Outfalls 002 and 003, or effluent discharged from the CWTS, with the SW POC defined as Outfall 001). In both cases, the SW POE is the river. Seven SW parameters fail the source evaluation (1,4-dichlorobenzene, ammonia, bis(2-ethylhexyl) phthalate, ethylbenzene, pyridine, total xylenes, and total dissolved solids). Monitoring of these seven analytes should be continued at all three outfalls, as source ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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leachate (i.e., leakage to the ponds, or pass-through of untreated leachate at the CWTS) could potentially impact water quality. While conditions for functional stability are not met, the following considerations are important: •

Stormwater Ponds: It could likely be demonstrated that the expected mass flux of leachate contained in a surface seep would not pose a risk to HHE at the stormwater pond outfalls after accounting for blending within the ponds. Alternatively, the ponds could be converted to function as infiltration basins. In this way, only ammonia would remain of concern under similar migration conditions as described for potential GW or indirect SW impacts above.

•

CWTS: The median DF that would be required to meet the standard (i.e., the extent of treatment that would be required to meet direct discharge criteria) for all seven failing parameters is 4.35. The highest DF required, that for ammonia, is only about 26. The statistically representative ammonia concentration in this regard is 129 mg/L, which is relatively mild. The overall level of treatment required by the CWTS is very low, meaning that treated effluent should readily meet all discharge criteria with very little risk of underperforming. As with the ponds, the CWTS outfall could be converted to a passive onsite (internal) discharge via an infiltration gallery with the land serving as a buffer to the river. In this way, only ammonia would remain of concern under similar migration conditions as described for potential indirect SW impacts above (as noted previously, the CWTS is too close to the river for leakage to be of serious concern with regard to deep percolation to the uppermost aquifer).

In summary, if the landfill and/or CWTS were to actually leak as conservatively evaluated herein, the dilution within the uppermost aquifer or upon subsurface migration to the river would mean that leachate constituents could be directly discharged to GW or indirectly discharged to SW via an infiltration gallery, with the potential exception of ammonia. Following additional risk analyses and/or modifications to leachate and water control systems as suggested above, alternative risk-based criteria for ammonia could be established and variances sought from the current GW standards and SPDES Permit to reflect these modifications. Alternatively, monitoring for ammonia under the status quo could be continued until leachate source concentrations fall below 60 mg/L and 12.5 mg/L, the target values for functional stability in SW and GW, respectively. Overall, based on findings from this evaluation, it can be concluded that MVLF meets all conditions for functional stability with respect to leachate with the exception of ammonia. 6.6.5

Requirements for Confirmation Monitoring

Potential impacts to GW and SW are evaluated separately in the Leachate Module because direct SW impacts are more immediate and have to do mainly with surface releases (seeps) or discharge of treated effluent, which are largely controllable, whereas GW impacts have mainly to do with uncontrollable subsurface leaks that could take time to manifest at the GW POC. SW impacts are generally easier to address than GW impacts because they typically involve only ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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above-grade migration route (i.e., are readily apparent) and the time-of-travel (TOT) to the SW POC is generally very fast (i.e., interrupting an impacting release of leachate to SW will have an almost instantaneous effect). However, as evaluated in previous subsections, exceptions to this generalization involve cases where there is potential for subsurface migration to a water body (indirect SW impact). At MVLF, three separate confirmation monitoring (CM) programs are required to reflect the three pathways for potential impacts: migration to GW; direct discharge to SW; and indirect migration to SW. Because leachate emerges naturally from the base of the landfill and drains under gravity, CM for the geotechnical condition of the landfill is not required as concern about leachate accumulation with the waste mass (the “bathtub” effect) is negligible. The guiding philosophy behind developing a CM program is that, where a high level of confidence exists that the long-term leachate management strategy (at MVLF, gravity drainage of leachate to the semipassive onsite CWTS with discharge to the river) presents a low or negligible threat to HHE such that the landfill is functionally stable, this should be demonstrated by monitoring for a performance-based period. CM is intended to provide an “early warning” of impact potential following modification to previous leachate controls, allowing appropriate corrective action to be taken before manifestation of significant impacts and non-compliance conditions. For this reason, the CM program should include a contingency plan for reacting to defined trigger conditions. Following completion of CM, PCC in the Leachate Module can be terminated once the entire leachate management system is fully passive, which is not currently the case at MVLF (the CWTS requires some minimal active operation of pumps and valves). Any residual leachaterelated cover monitoring and maintenance activities can be provided via the Cap Module. Consistent with the defined end use condition at MVLF, however, no changes should be made to the existing cover system and public access to the landfill property and use of onsite water resources should be restricted. 6.7

Groundwater Confirmation Monitoring

Under RCRA Subtitle D and State derivatives such as 6CRR-NY Part 360, a Detection Monitoring Program (DMP) is required to detect and appropriately respond to deterioration of GW quality that can be attributed to the presence of a landfill (per 40CFR §258.54). The purpose of the EPCC Groundwater Module is to provide a technical basis for demonstrating that the DMP (or other regulated GW monitoring program) has satisfied this basic requirement and has confirmed that such GW quality deterioration has not and will not occur (or that such changes may have occurred in the past, but are fully understood, remedied, and will not threaten HHE at present or in the future). The systematic procedures for development of a GW CM program are provided in Section 6 and Appendix E-3 of the EPCC Methodology Technical Manual (Appendix E of EREF, 2006). In brief, the approach is based on: ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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•

Calculating the time of travel (TOT) for a potential leachate release to migrate from an appropriate landfill release location to the downgradient GW POC;

•

Optimizing GW monitoring activities such that the duration and frequency of monitoring and the monitored indicator parameters are sufficient to demonstrate that GW has been monitored for a sufficient period to detect a release at the POC, if such release had occurred; and

•

Eventually terminating all GW monitoring through a process of geometrically decreasing SM program.

It is noted that, although beyond the strict requirement for GW monitoring established under Subtitle D, GW monitoring can also be used to provide an indication of subsurface gas migration, since dissolution of volatile organic compounds (VOCs) and other gas-related contaminants in groundwater can result from such migration. Therefore, in the interests of conservatism, the GW CM program should include monitoring of select VOCs as indicators of potential gas impacts to groundwater until CM in the Gas Module is completed. However, as this study assumes development of a GW CM program at MVLF in 2011, by which time it has already been demonstrated that the landfill is functionally stable with respect to LFG (Sections 5.7 and 5.8), monitoring for potential gas impacts to GW is not addressed here. 6.7.1

Calculating Time of Travel (TOT)

The TOT for a conservative, unattenuated parameter in groundwater (e.g., chloride) is used to define the leading edge of a potential leachate release based on an advective “particle tracking” approach. The TOT is calculated from: TOT = TOTVADOSE + TOTSAT

(Equation 6-2)

Where TOTVADOSE is the time taken for the conservative tracer to migrate vertically through the vadose zone from the base of the landfill to the top of the uppermost aquifer and TOTSAT is the time taken for the tracer to migrate horizontally in the saturated zone from this point to the GW POC well. Potential Leachate Release Location: For the TOT calculation, the source is the most likely location(s) of a hypothetical leachate release. At MVLF, this is leakage at the base of the landfill (the CWTS is located on the alluvial plain adjacent to the river and thus is not of concern as a source of impacts to GW – leakage from the CWTS will rather manifest in SW). For unlined landfills lacking sumps but for which the base geometry is known, the most likely location for a leachate release is the downslope toe of the landfill. At MVLF, this is the leachate collection pipe (LCP) trench (Figure 2-4). Groundwater POC Location: The GW POC is defined in 40CFR §258.2 and §258.40(d) as a location where the uppermost groundwater bearing stratum can be monitored that is not more ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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than 450 feet from a vertical planar surface located at the hydraulically downgradient limit of the landfill on land owned by the owner of the facility. At MVLF, the GW POC is well MW-11C, which is located a horizontal distance of 145 feet from the LCP trench at the downslope landfill toe in the predominant direction of groundwater flow (based on Drawing 1, Appendix A of MMCE, 2012). Calculation of TOTSAT: The simple, conservative EPCC procedure for calculating TOT assumes one-dimensional flow within saturated media. TOTSAT is calculated as the horizontal flow distance in saturated media divided by the flow velocity, which is estimated by making simplifying assumptions 18 using the following variation on Darcy’s Law:

(Equation 6-3) Where: V = groundwater flow velocity (feet/day) K = saturated horizontal hydraulic conductivity (feet/day) i = flow gradient (feet/feet) ne = effective porosity (dimensionless) Replicating values previously input to Equation 6-1 in Section 6.4.2 and with reference to Table 2-1, K = 0.19 feet/day and i = 0.07 feet/feet. A value for ne = 0.464 is assigned, based on the default value for total porosity in the HELP Model for soil texture #11 for USCS soil classification “CL” (and which ASTM D2487-06 suggests may be used to represent shale). Based on this, V = 0.0287 feet/day, or about 10 feet per year. This yields TOTSAT = 145/10 = 14.5 years. Calculation of TOTVADOSE: TOTVADOSE is calculated as the vertical flow distance divided by vertical flow velocity, again estimated using the simplified variation on Darcy’s Law given in Equation 6-3 in which a maximum vertical gradient (i.e., a unit hydraulic gradient, i = 1.0) and saturated vertical hydraulic conductivity, K, in media above the uppermost aquifer are assumed. The vertical hydraulic conductivity of the gray till is given as 1×10-8 cm/s (Table 2-1), which equates to 0.000028 feet/day. A value for ne = 0.464 is again assigned, based on the default value for total porosity in the HELP Model for soil texture #11 for USCS soil classification “CL.” Based on these values, V = 6×10-5 feet/day, or about 0.022 feet per year. 18 The main assumptions applied are: (i) the effects of thermal and chemical energy potentials are ignored, as are the effects of frictional resistance, molecular attraction, and other mechanical forces (i.e., mechanical energy is considered only in terms of advective transport); (2) the aquifer is assumed to be homogeneous and isotropic with water moving only in one direction; and (3) only steady-state groundwater flow in effective porous media is considered. If the advection-only approach is considered an overly simplified for a given site and sufficient data is available, or if flow in fractured bedrock is to be considered in more detail, a more in-depth analysis of groundwater flow characteristics should be undertaken by a qualified hydrogeologist.


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The LCS at the base of the landfill drains to the LCP trench at downslope toe of the landfill, which is constructed in the gray till at an elevation of approximately 435 ft-msl. The gray till overlies bedrock, the uppermost aquifer. The ground surface at POC well MW-11C is reported as 427.5 ft-msl, with top of bedrock at a depth of 77 feet below ground surface (i.e., elevation 350.5 ft-msl). Therefore, the vertical distance between the LCP trench and top of bedrock is assumed to be 87 feet. This yields TOTVADOSE = 87/0.022 = 3,950 years. Calculation of TOT: Using Equation 6-2, the groundwater TOT for the combined vertical (87 feet) and horizontal (145 feet) pathway between the LCP trench and GW POC well MW-11C is 3,950 years for the vertical pathway and 14.5 years for the horizontal pathway, a total of about 3,965 years. 6.7.2

Components of Groundwater Confirmation Monitoring

Results from the above TOT calculation show that a GW CM cannot reasonably be developed at MVLF because the duration required is excessive. This calculation has effectively demonstrated that leakage of leachate through the gray till to the bedrock is not of concern – if leakage of leachate through the base of the landfill were to occur, it would migrate laterally through more permeable zones in the alluvium/brown till rather than down through the gray till to the uppermost aquifer. Impacts resulting from leachate will thus manifest in SW and not in GW. In other words, leachate does not pose a risk to water quality in the confined uppermost aquifer. Siting the landfill above very low permeability till deposits is environmentally protective as the till provides natural containment to isolate local groundwater resources from the facility. Monitoring the bedrock for potential impacts from leachate is not useful and should be abandoned, especially as it has been demonstrated that only one parameter – ammonia – is still present in sufficient concentrations to theoretically impact GW quality at the POC. The low residual concentrations of ammonia in any small quantity of leachate slowly percolating down through the gray till would be readily attenuated long before reaching the bedrock. GW monitoring has already been conducted for long enough to show evidence of short circuiting if this had occurred. 6.7.3

Completion of Groundwater Monitoring

In summary of Section 6.7, there are no CM requirements with respect to groundwater. All monitoring of GW below the gray till should be abandoned. Monitoring of superficial GW above the gray till is required for ammonia only. The CM program should be developed to focus on superficial GW and surface water quality as described next. 6.8

Surface Water Confirmation Monitoring

As described in Section 6.6.4, water quality in the Mohawk River could potentially be impacted by leachate leaking from the landfill or CWTS and migrating to the river via superficial alluvium/brown till deposits (indirect impacts) or as a result of direct seepage and runoff of ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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leachate to an onsite stormwater pond or effluent discharge from the CWTS (direct impacts). Different CM programs are needed to address these potential indirect and direct impact mechanisms. 6.8.1

Indirect Impacts from Landfill Leakage

Groundwater monitoring can serve as a surrogate for surface water monitoring with regard to threats posed by subsurface leachate migration from the landfill to the river. The procedure for establishing a surrogate CM program for SW is similar to that described for a GW CM program. Unless explicitly stated herein, the basis of calculations is consistent with Section 6.7. Potential Leachate Release Location: Leachate collection pipe (LCP) trench (Figure 2-4) at the downslope toe of the landfill. POC Location: The surrogate SW POC is shallow well MW-11B (Figure 6-1), which is located a horizontal distance of 155 feet from the LCP trench in the predominant direction of groundwater flow (based on Drawing 1, Appendix A of MMCE, 2012). Calculation of TOTSAT: Using Equation 6-3, the horizontal flow velocity, V, in lenses of “more permeable materials” in the alluvium/brown till is calculated as 0.66 feet/day, or about 240 feet per year, based on horizontal hydraulic conductivity, K = 2.83 feet/day (Table 2-1), i = 0.07 feet/feet (Section 6.4.2), and ne = 0.3 (a value typically assumed by Geosyntec for silty/clayey sand). This yields TOTSAT = 155/240 = 0.65 years, or about eight months. Calculation of TOTVADOSE: Using Equation 6-3 with vertical hydraulic conductivity, K = 0.23 feet/day (from Table 2-1, assuming all material above the screen depth in MW-11B comprises brown till), i = 1.0 (unit hydraulic gradient), and ne = 0.464 (assuming brown till corresponds to USCS soil “CL” per Section 6.7.1), the vertical flow velocity, V, equates to 0.496 feet/day, or about 180 feet per year. The LCP trench is at approximate elevation 435 ft-msl. The ground surface at well MW-11B is reported as 427.6 ft-msl and the well is screened in the alluvium/brown till at a depth of 24-39 feet below ground level (i.e., the top of screen is at elevation 403.6 ft-msl). Therefore, the vertical distance between the base of the landfill and the POC well screen is assumed to be 31 feet. This yields TOTVADOSE = 31/180 = 0.17 years, or about two months. Calculation of TOT: Using Equation 6-2, the groundwater TOT for the combined vertical (31 feet) and horizontal (155 feet) pathway between the LCP trench at the downslope toe of the landfill and SW POC well MW-11B is two months for the vertical pathway and eight months for the horizontal pathway, a total of 10 months. Components of Confirmation Monitoring: following be established: •

Establishment of CM requires that each of the

Monitoring locations: MW-11B (POC) and MW-8 (POE)


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•

Analyte list: Only ammonia concentrations remain sufficiently high to threaten SW quality via this migration path. Therefore, the CM analyte list should include ammonia and chloride, the GW indicator parameter selected for the site (see Section 6.3.5).

•

Monitoring duration: months.

•

Monitoring frequency: The frequency of CM should typically be based on half the TOT between the POC and POE 19. The actual POE is the river; however, a surrogate GW monitoring well MW-8 serves as a better POE location. MW-8 located a horizontal distance of about 475 feet from MW-11B in the predominant direction of groundwater flow (based on Drawing 1, Appendix A of MMCE, 2012). At a horizontal flow velocity of 240 feet/year, the TOT between these two wells is ½×475/240 = 1 year. This exceeds the total CM duration; therefore, the frequency should be set as 10 months. This means that only one CM monitoring event is required.

•

Trigger events: Low and high triggers should be established for both ammonia and chloride as follows:

The total duration of CM is defined by the TOT, which is 10

o Low trigger: Background concentration, defined as the statistical control limit based on eight most-recent measurements of the parameter concentrations at upgradient shallow well MW-6A, calculated based on USEPA (1988). o High trigger: Applicable groundwater standard, which is 500 mg/L for chloride and 2 mg/L for ammonia. If a trigger event occurs, the first step in response will be to verify the exceedance by resampling before considering whether the event is truly attributable to a leachate release. While verification re-sampling is ongoing, the landfill remains subject to CM. After resampling and the situation is better understood and confirmed not to represent a threat to HHE, it might be determined that the GW Module should be reevaluated before regulatory groundwater monitoring is resumed. If the exceedance is not verified (i.e., either is not confirmed by re-sampling or is demonstrated to be attributable to an alternative source/cause), the background concentrations should be updated using the new information, and CM should be continued. If the exceedance is verified for a low trigger, it could indicate that a leachate release is migrating towards the POC. This would potentially result in discontinuing CM and reinitiating full GW monitoring while re-evaluating the Leachate Module for inaccurate assumptions (which could also affect the outcome of other modules). Completion of Confirmation Monitoring: If CM continues to completion in the absence of a high trigger event, leachate-related PCC is completed if other conditions for fully passive leachate management are met. 19

The rationale for defining the CM frequency in this way is that a potential leachate release could not travel past the POC further than half the distance to the POE before being detected. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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6.8.2

Indirect Impacts from Leakage from the CWTS

Similar to the process described in Section 6.8.1, GW monitoring can serve as a surrogate for SW monitoring with regard to threats posed by subsurface leachate migration from the CWTS to the river. Potential Leachate Release Location: LCP trench at the downslope toe of the landfill. POC Location: The surrogate SW POC is well MW-9A (Figure 6-1), which is located a horizontal distance of 200 feet downslope from the plan center of the CWTS (based on Drawing 1, Appendix A of MMCE, 2012). Calculation of TOTSAT: Using Equation 6-3 and the input parameters from Section 6.8.1 yields TOTSAT = 200/240 = 0.83 years, or ten months. Calculation of TOTVADOSE: The ground surface at the base of the CWTS and well MW-9A is at approximately the same elevation on the alluvial plain adjacent to the river. The top of the well screen is 6.5 feet below ground level. Using Equation 6-3 with the same input assumptions and parameters as in Section 6.8.1, TOTVADOSE = 6.5/180 = 0.036 years, or about two weeks. Calculation of TOT: Using Equation 6-2, the groundwater TOT for the combined vertical (6.5 feet) and horizontal (200 feet) pathway between the CWTS and SW POC well MW-11B is 10½ months. Components of Confirmation Monitoring: following be established:

Establishment of CM requires that each of the

•

Monitoring locations: GW monitoring well MW-9A serves as both the surrogate POC and POE.

•

Analyte list: Only ammonia concentrations remain sufficiently high to threaten SW quality via this migration route. Therefore, the CM analyte list should include ammonia and chloride, the GW indicator parameter.

•

Monitoring duration: months, rounded up.

•

Monitoring frequency: The frequency of CM should typically be based on half the TOT between the POC and POE or, if this is zero due to the POC and POE being co-located, half the TOT between the source and the POC. This means that two CM monitoring events are required, each after 5½ months.

•

Trigger events: Low and high triggers should be established for both ammonia and chloride as discussed in Section 6.8.1.

The total duration of CM is defined by the TOT, which is 11


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Completion of Confirmation Monitoring: If CM continues to completion in the absence of a high trigger event, leachate-related PCC is completed once leachate management is fully passive. 6.8.3

Direct Impacts from Landfill Seeps

Seven parameters regulated under the SPDES Permit for SW discharge fail the source evaluation, including 1,4-dichlorobenzene, ammonia, bis(2-ethylhexyl) phthalate, ethylbenzene, pyridine, total xylenes, and total dissolved solids (TDS). Therefore, direct seepage of leachate through landfill sideslopes and runoff to an onsite stormwater pond could theoretically impact water quality in the ponds as measured at Outfalls 002 and 003 (the SW POC locations in this regard). However, because of the small contaminant flux contained in a seep relative to the volume of water in the ponds, it is not expected that incidental seeps would pose a threat to HHE. This is reflected in the fact that routine monitoring of these outfalls in not required under the SPDES Permit, although composite sample data are required to be submitted annually in conjunction with discharge monitoring for the CWTS. Components of Confirmation Monitoring: While other components of CM related to leachate are ongoing, composite sampling at Outfalls 002 and 003 should be continued on an annual basis in accordance with the SPDES Permit requirement. However, analysis should only be required for the seven parameters listed above. Completion of Confirmation Monitoring: Over the longer-term, the EPCC Technical Manual recommends that monitoring for incidental seeps and breakouts is better addressed as a component of cap inspection rather than as a SW monitoring activity. Monitoring for seeps should continue until no seeps have been observed under steady state conditions for cap performance or additional leachate data show that all regulated parameters meet the SW standard at the source. The frequency of monitoring should be consistent with the cap inspection schedule. Observation of a seep should serve as a low trigger, the required response for which is a localized corrective action (cap repair) and demonstration that an impact to SW is not sustained. 6.8.4

Direct Impacts from CWTS Discharge

The seven SW parameters that fail the source evaluation (1,4-dichlorobenzene, ammonia, bis(2ethylhexyl) phthalate, ethylbenzene, pyridine, total xylenes, and TDS) require treatment at the CWTS. The level of treatment required is modest, meaning that treated effluent should readily meet discharge criteria with little risk of CWTS underperformance. However, monitoring of these seven analytes should be continued in treated effluent discharged via Outfall 001 (the SW POC in this regard) as pass-through of insufficiently treated leachate could potentially impact water quality in the river. Components of Confirmation Monitoring: Monitoring should be continued in accordance with the SPDES Permit, although analysis should only be required for the seven parameters listed above. Action level triggers and response actions are specified in the SPDES Permit. Initial ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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response actions are to undertake a short-term, high-intensity monitoring program for the parameter(s) in question, with additional reporting to NYSDEC. Longer term responses include reopening of the permit for revised action levels or effluent limits as long as water quality standards are not violated. Operation and maintenance (O&M) of the CWTS in accordance with MMCE (2012) is also required. Completion of Confirmation Monitoring: Completion of CM for direct impacts from CWTS discharge is not possible until all seven of the above SW parameters meet their respective SW standard at the source. 6.9

Transition to Passive Leachate Management (Future)

As summarized above, MVLF meets nearly all conditions for functional stability with respect to leachate. Leachate management at MVLF could be modified over the longer-term such that the single remaining migration route for leachate to the POE (Mohawk River) would be via superficial GW, with only ammonia remaining of potential concern. Recommended modifications are as follows: Leachate Management System: The onsite CWTS is a simple, low-maintenance system in which leachate and groundwater inflow and outflow functions passively by gravity. Some aspects of leachate/groundwater transfer, wetland treatment, and effluent discharge require the active operation of valve manholes and other relatively minor O&M activities are required as specified in MMCE (2012). Overall, however, it should be relatively easy to modify operation of the CWTS to be fully passive; for example, with all valves left open and manholes allowed to over flow as control structures. The CWTS outfall could be converted to a passive onsite (internal) discharge via a GW infiltration gallery with the land serving as a buffer to the river. Stormwater Ponds: The mass flux of leachate contained in a surface seep is unlikely to pose a risk to water quality in the ponds after accounting for blending. As such, monitoring for incidental seeps and breakouts is better addressed as a component of cap inspection rather than as a SW monitoring activity. This is the primary recommended approach. Alternatively, the ponds could be converted to function as GW infiltration basins. Once the above transitions have been made and confirmed to be performing as intended, alternative risk-based criteria could be established for ammonia and variances sought from the Part 703.5 standard and SPDES Permit conditions to reflect these modifications and allow transition to post-regulatory custodial care. Another, potentially simpler, option is to continue monitoring for ammonia under the status quo until leachate source concentrations fall below 60 mg/L, the target value for functional stability in SW. In other words, at this concentration, neither treatment nor attenuation in superficial groundwater is necessary for leachate to meet conditions for functional stability. Residual care requirements for the ponds and CWTS could be provided by a caretaker or landscape gardener under a custodial care program comprising property inspection and maintenance, which is primarily focused on the cap, rather than subject to a Part 360 Permit. ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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7.

FUNCTIONAL STABILITY WITH RESPECT TO THE FINAL COVER

7.1


7.1.1

Background

The Cap Module is the final component in the EPCC evaluation process because the final cover (cap) is not strictly an entity of PCC in itself, but exists primarily to control impacts to HHE as a result of leachate, LFG, or direct contact with waste. As such, the status of the Leachate and Gas Modules are generally dependent on a certain level of cap integrity being maintained, and this must be reflected in the cap inspection and maintenance program. The systematic approach used for evaluating the cap included the following: •

Evaluating the extent to which functional stability has been achieved with respect to settlement, which may impact cap stability and performance;

•

Demonstrating that the cap design and performance is consistent with requirements of the end use strategy and outcomes from previous modules; and

•

Defining long-term cap monitoring and maintenance requirements.

In the latter regard, evaluation of the cap is expected to show that some inspection and care will be needed even after completion of regulated PCC and transition to custodial care in order to satisfy local land-use requirements, comply with deed restrictions and covenants, contain the waste in the landfill, and maintain functional stability in accordance with the outcomes of previous modules. A custodial care program would involve property management activities that are typical of any property, such as paying property taxes, controlling access, complying with local zoning ordinances, complying with the property use restrictions identified in the deed to the property, as well as de minimis oversight of cap integrity. 7.1.2

Procedural Basis

Updates to EPCC since its initial publication in 2006 have not directly affected the Cap Module; therefore, the systematic procedures for application of the module remain as specified in EPCC Methodology Technical Manual (Appendix E of EREF, 2006). Data requirements and other prerequisites are described in Section 3.6 of the manual while detailed evaluation procedures are provided in Section 7. 7.2

Site Features of Relevance to the Cap Module

Site features of relevance to the Cap Module include: •

Final cover design and layout

•

Design and operation of the LFG management system


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•

Waste in place and composition

•

Design and operation of the leachate management system

•

Stormwater management system

Details are provided in Section 2, with sources of information available listed in Section 1.4. 7.3

Prerequisites

The prerequisites for performing an evaluation in the Cap Module are reviewed below. It is assumed that 1992 represents year zero for PCC at MVLF as waste placement ceased in 1991. Therefore, meeting of prerequisite conditions is assessed relative to this date. 7.3.1

End Use Strategy

To evaluate the Cap Module, there should be a defined end use condition for the landfill property that identifies an acceptable range of cap performance criteria based on regulatory considerations and institutional controls. At MVLF, it is assumed that the end use of the property will be as green space set-aside with human contact minimized through physical and institutional controls (see Section 4). Consistent with 40CFR §258.51(c)(3), this ensures that post-closure use of the property do not disturb the integrity of the final cover or other components of the containment system. Access to the site should continue to be controlled through maintenance of perimeter fencing. Institutional controls should be maintained to preclude the consumption of groundwater or surface water at the site. 7.3.2

Outcomes from Previous Modules

The outcomes from the Leachate and Gas Modules are consistent with the end use strategy. Evaluations in both modules were successfully completed on the assumption that the existing allsoil cover design and passive stormwater management system (see Section 2.2.3) will remain in place and function as currently specified for the very long term. In brief: •

Leachate Module: The module outcome is based on the assumption that the existing final landfill cover remains in place and that leachate will continue to gravity drain from the base of the landfill to minimize retention of leachate within the waste and geotechnical stability issues. By 2011, functional stability with respect to leachate is largely achieved, meaning that passive leachate management should be possible. The continued presence of the cover system as a barrier to increased infiltration is expected to limit future increases in leachate generation or significant changes in redox potential.

•

Gas Module: By 2002, the LFG generation potential reached a de minimis level that met conditions for functional stability and allowed complete discontinuation of active gas management. Former LFG wells remain as cover penetrations and serve as passive vents.


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The continued presence of the cover system as a barrier to increased infiltration is expected to limit potential reactivation of pockets of increased waste degradation and gas generation. Defining the long-term stable condition of the landfill is made considerably simpler by the fact that there are no geosynthetic components in either the liner or cap, which means that typical concerns about degradation and loss of performance of these materials are non-issues at MVLF. 7.3.3

Cap Inspection and Maintenance Program

The outcome from the Leachate and Gas Modules, as well as the defined end use condition, assume that the existing cover design and stormwater management system will remain in place and be inspected, maintained, and repaired as necessary to retain their current performance characteristics. The existing post-closure inspection and maintenance program is sufficient to provide this level of ongoing performance (see Section 2.5). 7.4

First Cap Module Evaluation C1-Y5 (1997)

Completing a broad evaluation of all EPCC modules within five years of entering PCC should provide a useful “first look” at how the site is performing and whether sufficient data are being collected. This helps set expectations and make informed decisions about the timing and potential scope of future modifications that will be possible. Entering this evaluation with the perspective of an “EPCC Consultant” with the information available in 1997, it is anticipated that Evaluation C1-Y5 would serve primarily to suggest when the next follow up evaluation should be scheduled. Raw data, input assumptions, and detailed results from Evaluation C1-Y5 are provided in Appendix 4. A summary of pertinent findings is provided in the remainder of this section. 7.4.1

Evaluation of Post-Closure Settlement

The most important process in assessing functional stability with respect to the cap is developing a quantitative estimate of remaining settlement, because significant differential settlement is likely to be the limiting factor for the long-term stability and integrity of the cap. Depending on waste type and operating efficiency during placement, primary (mechanical) settlement is generally completed one to two years after cover construction. Therefore, it is reasonable to assume that significant settlement during the post-closure period will be limited to secondary settlement resulting from waste degradation. Calculating secondary settlement is based on estimates of past LFG generation and the fraction of the total LFG still to be produced, as suggested by Leonard et al. (2000). Secondary settlement can be estimated based on the following equation:


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(Equation 7-1) Where: S = Settlement rate (%) LFGC = Future area under the LFG generation curve at the time of closure, C LFGT = Future area under the LFG generation curve at time T LFGT-1 = Future area under the LFG generation curve at time T-1. Estimates of all LFG terms in Equation 7-1 can be derived using the LandGEM model to model waste degradation and gas generation (USEPA, 2005). The future area under the gas curve is generally defined as the 100-year period following initial waste placement. Significant secondary settlement is assumed complete (i.e., the cap is functionally stable) when it can be demonstrated that the annual rate of settlement is de minimis. In the context of predicting when conditions for functional stability may be reached, this is considered to be when settlement is less than 5% annually relative to the cumulative total post-closure volume reduction at the landfill (Morris and Barlaz, 2011). Thereafter, the actual condition of the cap is established through site-specific confirmation monitoring (CM). Figure 7-1 is a LandGEM-derived projection of the rate of post-closure secondary settlement expected at MVLF based on expected LFG generation over a 100-year period from 1976 through 2076. This evaluation is closely linked to the LFG evaluation. As such, input assumptions discussed in reference to LFG modeling in Evaluation G1-Y5 (Section 5.4) also apply here. In brief, the waste in place was conservatively assumed at about 1.7 million Mg placed between January 1976 and December 1991. Default input values from the EPA’s AP-42 document (USEPA, 1995) were assumed for the methane generation potential (L0 = 100 m3/Mg), methane content (50%), and mean collection efficiency (75%). The decay constant (k) was assumed as 0.08/year rather than the AP-42 default value based on visual comparison to the best-fit exponential trend line to the data and consistent with values proposed for “wet” landfills, which is appropriate given the reported history of liquid waste acceptance and groundwater infiltration at MVLF. Evaluation of expected annual settlement in Figure 7-1 suggests that the annual post-closure settlement rate may reach the de minimis 5% rate by 2004 at MVLF, which is 12 years after closure.


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Figure 7-1: Evaluation C1-Y5, Modeled Post-Closure Settlement Rate

7.4.2

Cap Performance and Integrity

The post-closure inspections and monitoring data available for the period 1993 through 1997 suggest that the cap was providing the necessary durability, survivability, and aesthetic qualities. No issues with cover settlement or sideslope instability were reported, and there were no significant problems with stormwater runoff controls or the leachate and LFG management systems that were attributable to cap performance. Non-quantitative observation of the final cover based on third-party site reconnaissance in July 1995 indicated that the overall condition of the landfill cover and property was good (see aerial photograph in Figure 7-2). 7.4.3


As indicated on Figure 7-1, the main result of Evaluation C1-Y5 is that the estimated timeframe to achieve functional stability based on meeting the de minimis residual settlement criterion is 2004-2005 (i.e., Years 12 or 13 of PCC) based on modeled predictions. From the perspective of the EPCC Consultant in 1997, it would likely be recommended that a follow-up evaluation be performed, preferably in conjunction with reevaluation of the Gas Module, no later than 20042005.


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Figure 7-2: Aerial Image of the Landfill in July 1995

7.5

Second Cap Module Evaluation C2-Y9 (2001)

As discussed in relation to the Gas Module (Section 5.5), by 2000 WMNY was experiencing difficulties in operating the LFG system and LFGTE plant. Soon after, WMNY informed NYSDEC that they would begin to evaluate the feasibility of permanently decommissioning the LFGTE plant in favor of alternatives for LFG control, including continued active flaring, passive flaring, or passive venting. In the context of this retroactive study, it is assumed that WMNY would have responded to the above situation by retaining the EPCC Consultant to evaluate the feasibility of alternative LFG controls in August 2001, exactly four years after the initial evaluation and four years ahead of the anticipated schedule. Given the close link between the Gas and Cap Modules, it is assumed that reevaluation of the Cap Module would also have been requested. This will be denoted as the second Cap Module evaluation, occurring in 2001 in Year 9 of PCC (Evaluation C2-Y9). Raw data, input assumptions, and detailed results from Evaluation C2-Y9 are provided in Appendix 4. A summary of pertinent findings is provided in the remainder of this section. Unless explicitly stated herein, the basis of evaluations remains consistent with the explanations provided for previous Evaluation L1-Y5 in Section 7.4.


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7.5.1

Evaluation of Post-Closure Settlement

Figure 7-3 is a LandGEM-derived projection of the rate of post-closure secondary settlement expected at MVLF, again calculated using Equation 7-1. Input assumptions discussed in reference to LFG modeling in Evaluation G2-Y9 (Section 5.5) also apply here. In brief, the assumed methane content (50%) and gas collection efficiency (75%) remained consistent with AP-42. Iterative curve fitting was used to adjust the methane generation potential (L0) and decay constant (k) such that modelled gas results best mirrored the best-fit exponential trend line to the site data. Based on this, final input values were selected as L0 = 80 m3/Mg and k = 0.135/year. The k value is consistent with upper-bound values reported for very wet landfills and also matches the value independently suggested by a consultant during a third-party review of the site gas model several years ago.

Figure 7-3: Evaluation C2-Y9, Modeled Post-Closure Settlement Rate

As the graph indicates, the annual rate of post-closure secondary settlement attributable to waste degradation is expected to meet the de minimis 5% rate by 2002, slightly earlier than previously estimated in Evaluation C1-Y5. Overall, this evaluation indicates that functional stability with respect to cap settlement is expected in Year 10 of PCC.


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7.5.2

Cap Performance and Integrity

The post-closure inspections and monitoring data available for the period 1993 through 2001 again suggest that cap performance is stable. No issues with cover settlement or sideslope instability were reported, and there were no significant problems with stormwater runoff controls or the leachate and LFG management systems that were attributable to cap performance. Nonquantitative observation of the final cover based on third-party aerial reconnaissance in April 2003 (Figure 7-4) and June 2006 (Figure 7-5) indicate that the overall condition of the landfill cover and property was good around the time of Evaluation C2-Y9 and has remained stable in subsequent years. Vigorous vegetation appears to cover the entire landfill cap area (allowing for immediate post-winter conditions in the photograph in Figure 7-4). Stormwater swales and channels are well defined and clearly visible in both photographs, supporting WMNY’s reports that erosion and washout of structural materials has not been an issue since closure.

Figure 7-4: Aerial Image of the Landfill in April 2003


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Figure 7-5: Aerial Image of the Landfill in June 2006

7.5.3


As indicated on Figure 7-3, the main result of Evaluation C2-Y9 is that functional stability based on meeting the de minimis residual settlement criterion should be achieved in 2002 (i.e., Year 10 of PCC) based on modeled predictions. This finding is supported by that of Evaluation G2-Y9 (Section 5.5), which showed that functional stability with respect to gas has also been met in 2001 or will be very soon thereafter. For the purposes of an EPCC evaluation, the final cover system at MVLF can be described as stable at this juncture, subject to confirmation monitoring (CM) in which temporal topographic survey data are used to confirm modeled predictions on the rate of post-closure cover settlement. 7.6

Confirmation Monitoring

CM in the Cap Module is distinct from that of previous modules because several regulatory and containment requirements may apply to the cap. The outcomes of previous modules are also dependent on long-term cap performance. The ultimate goal of the Cap Module is to develop a long-term Cap Monitoring and Maintenance Program (CMMP) to facilitate final transition from a regulated PCC program to a post-regulatory custodial care program.


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7.6.1

Cap Settlement

To confirm that actual cap settlement rates are consistent with modeled predictions, topographic survey data are needed to calculate reductions in the landfill volume over time (which can be translated to settlement). This requires as-built surveys of the entire landfill cover immediately after construction (to provide peak cover elevations at closure to serve as the “baseline” for calibrating post-closure settlement) followed by at least two site-wide surveys during the postclosure period. At MVLF, as-built surveys of the landfill cover were conducted as part of closure construction but no subsequent surveys have been conducted, which means that CM for cap settlement cannot be conducted. However, the site is now 12 years past the date at which functional stability with regard to cap settlement was expected, and routine inspection of the cover since closure (a further 10 years back) has not indicated any significant issues related to differential settlement or subsidence leading to surface irregularities, damage, poor drainage, or ponding of water. Therefore, for this study it is reasonable to assume that CM is no longer required. The current rate of settlement is expected to be very low (less than 1% annually, based on Figure 7-3) such that several years between surveys would be needed to show meaningful differences. 7.6.2

Cap Inspection and Maintenance Program

The outcome from the Leachate and Gas Modules, as well as the defined end use condition, assume that the existing cover design and stormwater management system will remain in place and be inspected, maintained, and repaired to retain current levels of performance. Tables E-7-2 and E-7-3 in Section 7 of the EPCC Technical Manual provide a thorough summary of performance requirements for cap containment and non-containment functions, along with examples of how these requirements should be applied in a CMMP and examples of what could constitute high and low trigger events. With regard to cap performance, the existing post-closure inspection and maintenance program at MVLF (see Section 2.5) addresses most of the topics expected, but is much less comprehensive than the description contained in the above tables. Notwithstanding, the current program at MVLF is approved and thus is considered adequate by NYSDEC, and there are no known current problems with the cap. Overall, it is concluded that the cap (and related monitoring/maintenance procedures) meets post-closure requirements. Further, provision of care in accordance with the current program is sufficient to maintain the outcomes of the Leachate and Gas Modules. Following transition to passive leachate management with internal discharge as suggested in Section 6.9, the current program could serve as the basis for negotiation with NYSDEC for development of a custodial care program and completion of regulated PCC.


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8.

SUMMARY AND CONCLUSIONS

8.1

End Use Strategy

For simplicity, in this study it was assumed that the property will be as green space set-aside with human contact minimized throughout the post-closure period and beyond into custodial care. As such, it was assumed that: •

Access to the site will be controlled through maintenance of perimeter fencing;

•

Institutional controls preclude the consumption of groundwater or surface water at the site;

•

Leachate will continue to be drained passively from the base of the landfill; and

•

The existing cover system and other surface features such as the stormwater management system will remain in place, function as currently specified for the very long term, and be inspected, maintained, and repaired as necessary to retain the character of the landscape.

This simple end use strategy was effective in this study, allowing demonstration of functional stability with regard to LFG, leachate, and the cap. This supports the EPCC prerequisite that the end use condition of the landfill property be established as a baseline against which to assess functional stability. Defining the end use condition also assists in orientating the evaluation in consideration of the long-term plans for the property and the performance requirements for the landfill unit between different modules. For example, the continued presence of the cap as a barrier to increased infiltration is expected to limit future increases in leachate generation or significant changes in redox potential (and, by association, leachate chemistry) as well as potential reactivation of pockets of increased waste degradation and gas generation. Defining the long-term stable condition of the landfill for this study was made considerably simpler by the fact that there are no geosynthetic components in either the liner or cap, negating typical concerns about long-term degradation and loss of performance of these materials. 8.2

Landfill Gas Management

Evaluation of LFG management using EPCC provides a technically defensible assessment of when it would be acceptable to transition from active to passive LFG management and/or reduce or terminate methane migration monitoring based on a demonstration of functional stability with respect to LFG (i.e., no threat to HHE in the absence of active LFG control). 8.2.1

Key Findings

Two retroactive evaluations were performed in this study, the first in 1997 (Evaluation G1-Y5, in Year 5 of PCC) with a follow up in 2001 (Evaluation G2-Y9, in Year 9 of PCC). Principal


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findings are summarized in Table 8-1, with all timeframes measured relative to the start of PCC in 1992. Table 8-1: Summary of Gas Module Evaluations Methane Trend

Timeframe(s) for Functional Stability

Observations

Evaluation G1-Y5 (1997) Linear regression: 216 Downward, scfm R2 > 0.5 Sen’s test: Downward Evaluation G2-Y9 (2001)

2005 (Year 13 of PCC), based on measured LFG collection data 2015-2018 (Years 13-26 of PCC), based on modeling

The flare remains the BACT, because methane flow is twice the typical industry standard of 100 scfm as a practical lower-bound cutoff for active flare operation

Linear regression: Downward, R2 > 0.8 Sen’s test: Downward

2002-2007 (Years 10-15 of PCC), the earlier date is based on direct extrapolation of site measurements, later date is based on modeling

The flare cannot function viably given existing gas flows Passive venting as the primary means of residual gas control supplemented with the methane oxidation capacity of the all-soil cover system can represent the BACT Recommend transition to passive gas management in 2002 and conduct Confirmation Monitoring

8.2.2

Methane Flow

93 scfm


Abandoning active LFG management in favor of passive venting at MVLF was approved by NYSDEC in 2002. However, for this study a hypothetical Confirmation Monitoring (CM) program was developed based on the layout of the site relative to the gas POE (property boundary) and POC. The POC was assumed as a probe GP01, located approximately 35 feet from the toe of the landfill in the direction of the nearest potential sensitive receptor (an occupied house), and equidistant from the western property boundary. The duration of CM based on the maximum time of travel (TOT) for gas migration in the vadose zone from the landfill toe to probe GP01 was 21 months, with monthly monitoring required. While gas CM is ongoing, it was assumed that monitoring of potential gas impacts (i.e., selected VOCs) to groundwater was also continued at well MW-14. In the context of this CM program at MVLF, it is assumed that monthly CM would have been initiated in July 2002, at the time that NYSDEC approved transition to passive gas venting. CM would have been scheduled to be completed in April 2004. WMNY reports that monitoring data records at MVLF showed that no gas impacts were detected at perimeter probes or groundwater wells during this period; therefore, eliminating active LFG controls and converting to a fully passive venting system is an acceptable and sustainable long-term method of LFG management. Conditions for functional stability have been demonstrated with respect to LFG.


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8.2.3

Data Needs

All data critical to the evaluations have been collected. However, LFG temperature data are useful for validating findings from LFG modeling (Morris et al., 2013). In addition, gas migration probe monitoring data, in particular since elimination of active LFG controls in 2002, would be useful in allowing a more in-depth demonstration of the process of CM in the Gas Module. 8.3

Leachate Management

Demonstrating that leachate is not a potential threat to HHE is a primary driver for functional stability through the process of optimization and elimination of active leachate management, based on EPCC’s definition that a closed landfill is functionally stable when it does not present a threat to HHE at the POE, with the POE identified as the closest location at which a receptor could be exposed to contaminants and receive a dose by a credible pathway from the landfill. Three retroactive evaluations were performed in this study, the first in 1997 (Evaluation L1-Y5, in Year 5 of PCC) with follow ups in 2002 (Evaluation L2-Y10, in Year 10 of PCC) and 2011 (Evaluation L3-Y19, in Year 19 of PCC). All timeframes are measured relative to the start of PCC in 1992. 8.3.1

Key Findings – “Gateway” Indicators of Functional Stability

The leachate management strategy at MVLF was that leachate would gravity drain from the base of the landfill to onsite storage tanks ETANK and WTANK, with ETANK used to represent overall leachate quality. However, the mechanism for onsite storage of leachate in tanks prior to offsite trucking for WWTP disposal was abandoned in favor of full onsite management using a constructed wetland treatment system (CWTS) in 2012. Evaluation L3-Y19 in 2011 reflects this planned change in strategy. A statistically significant decreasing trend in BOD to a representative value below a threshold of 100 mg/L and an absolute BOD/COD ratio below 0.1 are used as “gateway” indicators of the onset of functional stability conditions in leachate. Principal findings in this regard are summarized in Table 8-2. Overall, values in Table 8-2 are progressively lower for all indictors, suggestive of increasingly mild leachate and high levels of biodegradation and stability developing within the waste mass. In each evaluation, this step provides a high level of statistical confidence that leachate quality will continue to improve with time.


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Table 8-2: Summary of Leachate Module Evaluation of “Gateway” Indicators BOD Trend Threshold: Downward Trend

BOD Concentration Threshold: BOD < 100 mg/L

BOD/COD Ratio Threshold: BOD/COD < 0.1

165.6 mg/L (ETANK) 39.1 mg/L (WTANK) BOD concentrations expected to routinely meet the threshold around 1997 for ETANK and 1995 for WTANK

Broadly decreasing trend in BOD/COD ratio, but BOD/COD stability threshold not routinely met

35.1 mg/L (ETANK) 80.7 mg/L (WTANK) BOD concentrations have not exceeded the threshold since January 2000 (ETANK) or April 1996 (WTANK)

Threshold routinely met in ETANK since April 2000 (only three of 26 values have exceeded 0.1 since October 1995)

17.9 mg/L (ETANK) 5.4 mg/L (WTANK) BOD concentrations have exceeded the threshold only once since January 2000 (ETANK) and April 1996 (WTANK)

With very few exceptions, threshold value routinely met in ETANK and WTANK

Evaluation L1-Y5 (1997) Linear regression: Downward, R2 = 0.57 (ETANK) R2 = 0.42 (WTANK) Sen’s test: Downward Evaluation L2-Y10 (2002) Linear regression: Downward, R2 = 0.76 (ETANK) R2 = 0.62 (WTANK) Sen’s test: Downward Evaluation L3-Y19 Linear regression: Downward, R2 = 0.78 (ETANK) R2 = 0.71 (WTANK) Sen’s test: Downward

8.3.2

Key Findings – Evaluation of Threat to Human Health and the Environment

Building on the above, potential threats posed by leachate to HHE were retroactively evaluated based on comparison of leachate quality to applicable water quality standards at the source or POC. Potential pathways for leachate migration used in the evaluations are leakage of leachate into the subsurface through the base of the landfill and direct migration to groundwater (GW) in the underlying bedrock (Utica Shale, the uppermost aquifer); leakage of leachate into the subsurface through the base of the landfill and indirect migration via the superficial alluvium/brown till to surface water (SW) in the Mohawk River; and direct seepage and runoff of leachate to an onsite stormwater pond. For Evaluation L3-Y19, leakage from the CWTS to superficial GW and direct discharge of treated effluent from the CWTS are also applicable. Principal findings from the three sequential evaluations summarized in Table 8-3.


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Table 8-3: Summary of Leachate Module Evaluation of Threat to HHE Groundwater Source Evaluation Evaluation L1-Y5 (1997) Parameters: 51 PASS: 25 (49%) FAIL: 26 (51%) No Data: Zero Ammonia is worst case failure, requiring dilution factor (DF) >200 to meet limit value Evaluation L2-Y10 (2002) Parameters: 51 PASS: 31 (61%) FAIL: 20 (39%) No Data: Zero Ammonia is worst case failure, requiring DF >100 to meet limit value Evaluation L3-Y19 Parameters: 51 PASS: 38 (74.5%) FAIL: 13 (25.5%) No Data: Zero Ammonia is worst case failure, requiring DF >64 to meet limit value

Groundwater POC Evaluation

Surface Water Source Evaluation

Surface Water POC Evaluation

Remaining Parameters: 26 DF at POC: 6.25

Parameters: 53 PASS: 24 (45%) FAIL: 28 (55%) No Data: 1 (dissolved O2) Ammonia is worst case failure, requiring DF >200 to meet limit value


Parameters: 53 PASS: 31 (59%) FAIL: 21 (40%) No Data: 1 (dissolved O2) Ammonia is worst case failure, requiring DF >200 to meet limit value


Parameters: 41 PASS: 34 (83%) FAIL: 7 (17%) No Data: Zero Ammonia is worst case failure, requiring DF >26 to meet limit value


PASS: 12 (46%) FAIL: 14 (54%) Overall Fail: 28%

Remaining Parameters: 20 DF at POC: 6.25 PASS: 9 (45%) FAIL: 11 (55%) Overall Fail: 22% Remaining Parameters: 13 DF at POC: 6.25 PASS: 11 (85%) FAIL: 2 (15%) Only ammonia and color fail the evaluation Overall Fail: 4%



PASS: 6 (86%) FAIL: 1 (14%) Only ammonia fails the evaluation Overall Fail: 3%

Values in Table 8-3 indicate progressive, meaningful improvement of leachate quality with time and increasingly high levels of biodegradation and stability within the waste mass. This is consistent with the gateway indicators and vindication of EPCC’s use of the indicators in this way. 8.3.3


Results from time of travel (TOT) calculations in Section 6.7 show that a CM program for GW cannot reasonably be developed at MVLF because the duration required for monitoring would be excessive at nearly 4,000 years, due mainly to the very long TOT for vertical migration through the gray till overlying the bedrock (uppermost aquifer). This calculation effectively demonstrated that leakage of leachate through the gray till to the bedrock is not of concern – if leakage of leachate through the base of the landfill does occur, it will migrate laterally through more permeable zones in the alluvium/brown till rather than down through the gray till. Impacts ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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resulting from leachate will thus manifest in SW and not in GW. This is not a failure in the EPCC process, but rather a successful demonstration that the landfill was sited well. The very low permeability gray till provides natural containment to isolate local groundwater resources. It is recommended that all monitoring of GW below the gray till should be stopped. Development of CM programs focused on superficial GW and surface water was described in detail in Section 6.8. Monitoring of superficial GW above the gray till is required for ammonia (the remaining impacting analyte) and chloride (the indicator parameter) only. CM is required for less than one year. 8.3.4

Data Needs

Most data critical to the evaluations have been collected. However, a more in-depth evaluation of the Leachate Module would have been possible if leachate flow data were available. If it can be demonstrated that leachate production is decreasing along with leachate quality, this provides very high levels of confidence in conclusions drawn based on the latter, because the potential mass load (i.e., concentration × volume) of any future leachate release would be lower than the current mass load in terms of both the concentration and volume terms. 8.4

Final Cover Settlement and Integrity

The cap is not strictly an entity of PCC in itself, but exists primarily to control impacts to HHE as a result of leachate, LFG, or direct contact with waste. As such, the status of previous evaluations is generally dependent on a certain level of cap integrity being maintained, and this must be reflected in the long-term cap monitoring and maintenance program (CMMP) developed using the EPCC Technical Manual. Nevertheless, demonstrating the extent to which functional stability has been achieved with respect to settlement, which may impact cap stability and performance, is a cap-centric evaluation. 8.4.1

Key Findings

Two retroactive evaluations of cap settlement were performed in this study, the first in 1997 (Evaluation C1-Y5, in Year 5 of PCC) with a follow up in 2001 (Evaluation C2-Y9, in Year 9 of PCC). All timeframes are measured relative to the start of PCC in 1992. EPCC assumes that significant post-closure settlement will be limited to secondary settlement resulting from waste degradation, which can be modeled based on past LFG generation and the fraction of the total LFG still to be produced. Significant secondary settlement is assumed complete (i.e., the cap is functionally stable) when it can be demonstrated that the annual rate of settlement is de minimis, or when settlement is less than 5% annually relative to the cumulative total post-closure volume reduction at the landfill. Evaluation C1-Y5 indicated that the annual post-closure settlement rate at MVLF may reach the de minimis 5% rate by 2004, 12 years after closure. Follow up Evaluation C2-Y9 showed this rate is expected by 2002, slightly earlier than the previous estimate. Overall, functional stability ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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with respect to cap settlement is expected in Year 10 of PCC. This finding is supported by that of Evaluation G2-Y9 (Section 5.5), which showed that functional stability with respect to gas has also been met in 2001 or will be very soon thereafter. 8.4.2


To confirm that actual cap settlement rates are consistent with modeled predictions, topographic survey data are needed to calculate reductions in the landfill volume over time (which can be translated to settlement). This requires as-built surveys of the entire landfill cover immediately after construction (to provide peak cover elevations at closure to serve as the “baseline” for calibrating post-closure settlement) followed by at least two site-wide surveys during the postclosure period. At MVLF, as-built surveys of the landfill cover were conducted as part of closure construction but no subsequent surveys have been conducted, which means that CM for cap settlement cannot be conducted. However, the site is now 12 years past the date at which functional stability with regard to cap settlement was expected, and routine inspection of the cover since closure has not indicated any significant issues related to differential settlement or subsidence leading to surface irregularities, damage, poor drainage, or ponding of water. WMNY reports there has been little to no cap repair required since closure. Therefore, for this study it is reasonable to assume that CM is no longer required. The current rate of settlement is expected to be very low (less than 1% annually, based on Evaluation C2-Y9) such that several years between surveys would be needed to show meaningful differences. 8.4.3

Data Needs

With the exception of topographic land or flyover surveys of the landfill cover since completion of closure construction in 1993 to conduct CM (a largely academic exercise as outlined above), no additional cap-related data or site information is needed. 8.5

Transition to Custodial Care

Active LFG management was completed in 2002, the same year that cap settlement was expected to meet conditions for functional stability. By 2011, leachate is on the brink of meeting all conditions for functional stability. If the recommended modifications are made to the CWTS for passive (internal) discharge via GW infiltration, the only remaining migration route for leachate to the Mohawk River would be via superficial GW, with ammonia the single remaining analyte of potential concern. Monitoring for incidental seeps and impacts to the ponds is better addressed as a component of cap inspection rather than as a SW monitoring activity or the ponds could also be converted to function as GW infiltration basins. Once transitions to residual leachate management have been made and confirmed to be performing as intended, alternative risk-based criteria could be established for ammonia and variances sought from the Part 703.5 standard and SPDES Permit conditions to reflect these modifications and allow transition to post-regulatory custodial care. Another, potentially simpler, option is to continue monitoring for ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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ammonia under the status quo until leachate source concentrations fall below 60 mg/L, the target value for functional stability in SW. In other words, at this concentration, neither treatment nor attenuation in superficial groundwater is necessary for leachate to meet conditions for functional stability. With regard to cap performance, the existing post-closure inspection and maintenance program at MVLF addresses most of the topics expected for a CMMP as described in the EPCC Technical Manual, but is much less comprehensive. Notwithstanding, the current program at MVLF is approved by NYSDEC, and there are no known problems with the cap. Overall, it was also concluded that provision of care in accordance with the current program is sufficient to maintain the outcomes of the leachate and gas evaluations. Therefore, the existing program could serve as the basis for negotiation with NYSDEC for development of a custodial care program and completion of regulated PCC subject to a Part 360 Permit. In addition to providing de minimis oversight of cap integrity and grounds maintenance, the custodial care program agreed with NYSDEC will require that the property owner satisfies local land-use requirements; complies with deed restrictions, covenants, and local zoning ordinances; and undertakes typical property management responsibilities such as paying property taxes and controlling access. Residual care requirements for the cap, stormwater swales and ponds, CWTS, and the grounds at MVLF could be provided by a caretaker or landscape gardener rather than a solid waste engineer or environmental scientist.


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REFERENCES ASTSWMO (2013) Subtitle C and Subtitle D post-closure care period final survey report. Prep. by the Association of State and Territorial Solid Waste Management Officials Post-Closure Care Workgroup, March 2013 Barlaz M.A., Rooker A.P., Kjeldsen P., Gabr M.A., Borden M.C. (2002) Critical evaluation of factors required to terminate the post-closure monitoring period at solid waste landfills. Environmental Science and Technology, 36, 3457-3464. Barlaz M.A., Cowie S.J., Staley B., Hater G.R. (2004) Production of non-methane organic compounds (NMOCs) during the decomposition of refuse and individual waste components under various operating conditions. Proc. SWANA’s 9th Annual Landfill Symposium, 21-25 June, Monterey, California Barlaz M.A., Chanton J.P., Hater G.R. (2009) Controls on landfill gas collection efficiency: Instantaneous and lifetime performance. J. Air and Waste Management Association, 59, 13991404 Barlaz M.A. (2012) Feasibility of waste sampling and analysis. Proc: 7th Intercontinental Landfill Research Symposium, 25-27 June, Lulea, Sweden Bookter T.J., Ham R.K. (1982) Stabilization of solid waste in landfills. J. Environmental Engineering, 108, 1089-1100 Bour O., Couturier C., Berger S., Riquier L. (2005) Evaluation des risques liés aux émissions gazeuses des décharges: propositions de seuils de captages (in French). INERIS-DRC-0546533/DESP-R01, Paris, France Caldwell M.D., Obereiner J.M., Morris J.W.F. (2016) Case study for prediction of a performance-based PCC term for LFG collection using passive controls. Proc. Global Waste Management Symposium, 31 January – 3 February 2016, Indian Wells, California CalRecycle (2010) Long-term postclosure maintenance and corrective action cost estimates and financial assurance demonstrations for landfills. California Department of Resources Recycling and Recovery, Local Enforcement Agencies: Regulation Implementation Guidance, 30 June 2010: http://www.calrecycle.ca.gov/lea/Regs/Implement/Postclosure/Monitoring.htm. Chanton J., Abichou T., Langford C., Spokas K., Hater G., Goldsmith D., Barlaz M.A. (2011) Observations on the methane oxidation capacity of landfill soils. Waste Management, 31, 914925 Crest M., Åkerman A., Morris J.W.F., Budka A., Presse D., Hayward-Higham S. (2010) Aftercare completion and the path to sustainable reuse of closed landfills. Proc. ISWA World Congress, 15-18 November 2010, Hamburg, Germany Environmental Protection Agency of Ireland (2011) Management of low levels of landfill gas. Prep. by Golder Associates Ireland Ltd for the EPA Office of Environmental Enforcement, Wexford, Ireland, April 2011 ME1165/MD15234.EPCC CASE STUDY.MVLF.FINAL.DOC

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