Vertical Soil Profiling Using the Color-Tec® Method at ...

Vertical Soil Profiling Using the Color-Tec® Method at Former NCBC Davisville During the summer of 2007, the Navy conducted a comprehensive vertical soil profiling study at the former Naval Construction Battalion Center (NCBC) Davisville in North Kingstown, Rhode Island as part of the Phase III Remedial Investigation of Site 16. The objective was to identify source releases and delineate chlorinated volatile organic (CVOC) plume(s). This project was innovative because it was the first large scale study to incorporate a semi-quantitative head-space based field screening method for soils to help identify source areas and to delineate the 3-D extent of a CVOC plume detected primarily in deep overburden and shallow bedrock groundwaters. Prior to this project, the Color-Tec® methodology was used primarily to screen groundwater samples collected via temporary wells and/or Hydropunch® sampling. The project was completed using the TRIAD approach. Project Background The former NCBC Davisville facility is located in the Town of North Kingstown, approximately 18 miles south of the state capital, Providence. At the time of Base Davisville (see Figure 1) comprised three areas: the Main Center (839 acres, Zones 1 West Davisville storage area (70 acres), and Camp Fogarty, a 375-acre training approximately 4 miles west of the Main Center.

Rhode Island, closure, NCBC through 4), the facility located

The mission of NCBC Davisville was to provide mobilization support to the active Naval Construction Force; to act as a mobilization base for the rapid assembly, outfitting, and readying of Reserve Construction Battalions; to store, preserve, and ship advanced base and mobilization stocks; and to procure, receive, pack, and ship collateral equipment for Atlantic, European, and Caribbean military construction projects. NCBC Davisville was comprised primarily of warehouse space and freight yards, most of which have been demolished or redeveloped (used for other purposes). Installation Restoration (IR) Program Site 16 is located in the eastern portion of the Site generally between Allen Harbor and Narragansett Bay (see Figure 2). Generally, the Site is composed of two areas – a developed area south of Davisville Road and east of Allens Harbor Road, and an undeveloped area north of Davisville Road and between Allens Harbor and Wescott Roads. The developed area includes the former Building 41 area, an old railroad spur area (previously undeveloped), Building 318 to the south, and Building 39 to the west. Most of the area is paved and is currently being used for the temporary storage of new cars delivered by ship and train pending delivery to dealers. The undeveloped area is primarily wooded with the exception of an asphalt-paved area in the center. An unnamed asphalt-paved road circles the outer perimeter of this portion of the site and was formerly used by the Navy for training construction equipment operators. In the past, this area was extensively bulldozed and disrupted during training exercises, but it now has a vegetative cover of trees, shrubs, and grasses. Installation and multiple rounds of sampling of approximately 200 wells and other traditional investigative procedures (soil sampling, synoptic groundwater events, Membrane Interface Probe sampling, seismic refraction surveys, etc.) performed over nearly 10 years of investigations preceding the Phase III investigation had not satisfactorily identified contaminant sources or adequately delineated the nature and extent of soil and groundwater CVOC impacts. In general, a CVOC plume extending from the eastern portion of former Building 41 to Allen Harbor is observed, with multiple potential source areas identified. However, while trichloroethene (TCE) was used in a solvent recovery still in the former Building 41, no definitive source releases are documented or were found during the Phase I and Phase II field investigations. However, TCE is found in the deep overburden and shallow bedrock downgradient of this area.

Selection of Color-Tec® Field Screening The Color-Tec® method was selected as a field screening tool for soils because it is a simple, quick and cost-effective method that produces real-time semi-quantitative results in the parts per billion (ppb) ranges with modest to high correlation with fixed-based laboratory results. Color-Tec® field screening has been demonstrated to be an effective tool in many investigations for CVOC, typically in groundwaterbased investigations in the Southern United States. It is used quite regularly to investigate former dry cleaning sites in Florida (where the technology was developed). While the Color-Tec® tool is more typically used to investigate groundwater contamination, the technology is focused on the analysis of head-space concentrations regardless of the source media (soils or groundwater). The Color-Tec® field screening method combines sample purging with colorimetric detector tubes that routinely detect low concentrations (< 5 ppb in groundwater) of CVOCs. Results are typically considered qualitative though site-specific semi-quantitative results can be approximated based on a comparison of Color-Tec® results to fixed-based laboratory results. The method itself is quite simple. For the Phase III investigation, approximately 15 grams of soils were added to a clean 40 ml unpreserved VOA vial and certified pure deionized water was added until approximately 30% headspace remained. The sample was quickly capped, shaken vigorously for 30 seconds and placed on ice until analysis. During analysis, the samples and colorimetric tubes were first heated in a water bath to 104 degrees Fahrenheit and then a hand-operated pump was used to pull the contents of the headspace into the colorimetric tube where a color change occurred if CVOCs were present. Typically, it takes less than 10 minutes from sample collection to Color-Tec® result. The analysis can be performed in the field though a central location such as a field trailer is preferred. In addition to the fact the methodology is simple to use and produces screening results very quickly, the cost per screening sample is very low ($10 to $15 per sample). The technical advantages of this screening method compared to other traditional VOC screening methods, such as the use of Photo-ionization detectors (PID) or Flame-ionization detectors (FID), are: 1) the lower detection limits achievable using Color-Tec® (single digit ppb versus 1000 ppb for PIDs or FIDs), and 2) the specificity of the screening technology (in this case, CVOCs versus VOCs). However, use of a PID is still recommended to assist in identifying where samples should be collected for screening via Color-Tec®. Disadvantages of the Color-Tec® field screening method include negative chemical interferences, particularly toluene and xylene. The presence of these chemicals suppresses the colorimetric response which underestimates the CVOC portion of the VOC response. Based on this investigation, concentrations of toluene and xylene less than 1,000 ppb do not appear to significantly impact the Color-Tec® results. Vertical Profiling using the Color-Tec® Screening Method A 3-D profile of the CVOC contamination underlying Site 16 was accomplished by the Color-Tec® screening of soils collected from Direct Push Technology (DPT) soil borings advanced across Site 16. Initially, a variably spaced coarse grid (biased based on previous investigations) was established and then refined based on real-time data collection. Over 1250 discrete soil samples were collected from approximately 150 soil borings. Discrete soil samples were collected from continuous soil cores every 5 feet at most locations with more frequent soil samples collected based on observed lithologies and PID responses. Soils samples were collected from both unsaturated and saturated conditions and mimicked Region I EPA sampling protocols which produce a 50% soil to water ratio. Three different colorimetric tubes, representing three different concentration ranges, were used during the Color-Tec® field screening process – LL, L and M. Generally, the LL tube was used for results less than 500 ppb, the L tube was used for results greater than 500 ppb and less than 5,000 ppb and the M tube

was used for results greater than 5,000 ppb. If previous investigative results were not available for a particular area (i.e., contaminant concentrations for an area were unknown), the lowest colorimetric tube was used (LL tube) as the initial field screening tube. In some instances, multiple colorimetric tubes were required to successfully screen a particular soil sample and to verify overlap in tube responses. For soil screening conducted during this investigation, it was determined that if a positive response was observed in the upper half of the tube (i.e., the high concentration end of the tube), the sample should be re-run with the next successive tube. Similarly, if field screening began on a higher concentration tube and nondetects were observed, the sample was re-run with the next lowest tube to ensure that positive screening results were not missed. The Color-Tec® results provided semi-quantitative results for immediate decisions for the subsequent placement of soil borings and the delineation of impacted/non-impacted areas based on comparisons to the fixed-base laboratory. Field screening and lithology information was collected and tracked electronically in real-time through the use of Panasonic TOUGHBOOK® field computers. Sample labels and Chains of Custody were prepared and submitted electronically as well. This allowed the Navy to evaluate and share field results with regulators on a daily basis. This screening data and real-time data review allowed the Navy to review decisions by the field operations leader concerning: 1) which samples to send to the fixed-base laboratory, 2) where additional samples should be collected and 3) the placement of well screened intervals. Performance Assessment of the Color-Tec® Screening Method to Fixed-Base Laboratory Approximately 400 soil samples spanning the full range of Color-Tec® results were sent to a fixed-base laboratory for analysis via standard EPA methodology. Of the 187 Color-Tec® non-detect results, 161 were confirmed by the fixed-base laboratory, an 86% success/match rate. Of the 26 positive fixed-base laboratory detections where the Color-Tec® results were non-detect, the total CVOC concentrations were less than 10 ppb for 24 of the samples (ranged from 0.7 to 9.1 ppb). For the remaining two samples which were above 10 ppb, the fixed-base laboratory results were 20.6 ppb and 46 ppb. The geometric mean of these 26 fixed-base laboratory detections is 2.9 ppb. Of the 108 positive Color-Tec® results, 107 were verified by the fixed-base laboratory, a 99% success/match rate. The one false negative occurred where significant toluene and xylene concentrations were observed (4,100 ppb toluene, 11,000 ppb xylene). Comparison of the fixed-base laboratory results to the Color-Tec® results demonstrated significant site-specific correlation (see Figures 3, 4 and 5). For the three colorimetric tubes used, results generally clustered on lower and upper ends – effectively splitting the tube responses in two. There was also overlap in fixed-base laboratory results between the successive tubes. For instance, fixed-base laboratory results for LL tube readings of 1.5 to 3.0 were associated with fixed-base lab results ranging from approximately 100 ppb to 2,000 ppb, nearly identical to the observed range from approximately 100 ppb to 3,000 ppb for the 0 to 10 tube reading on the L tube. Generally, degree of correlation increased with concentration and tube types. Application of Color-Tec® Screening Results While correlation between Color-Tec® and fixed-base laboratory results were quite reasonable, ColorTec® results were not directly translated to an estimated fixed-base laboratory result in real-time during the field investigation. Rather, tube responses were assigned an estimated fixed-base laboratory result based on the geometric mean of all fixed-based laboratory results over a particular tube type and response range. The following summarize the estimated fixed-base laboratory result for each tube type and response:

• • • • • • •

non-detect (0 ppb) for no LL tube response, 16 ppb for LL tube responses of 0.05 to 1.5, 260 ppb for LL tube responses of 1.5 to 3.0, 860 ppb for L tube responses of 0 to 10, 5,400 ppb for L tube responses of 10 to 25, 2,200 ppb for M tube responses of 0 to 25, and, 12,000 ppb for M tube responses of 25 to 100

While this method may over- or under-estimate the correlated fixed-base laboratory result, this method allowed for quick estimations of approximate responses. From this estimation process, quick real-time decisions can be made. Using the estimated fixed-base laboratory result based on the colorimetric tube response for the approximately 1250 soil samples collected, source areas not previously known were identified and a significant refinement to the lateral and vertical extent of the soil and groundwater plumes was realized. The Color-Tec® screening results and fixed-base laboratory data was analyzed spatially across the site. To analyze the lateral extent of contamination, a series of slices through the site in 10 foot thick sequences were constructed. Figure 6 depicts an example 10 foot thick slice through the Site and demonstrates the fine scale resolution that is obtained utilizing the Color-Tec® screening method. Individual migration pathways can be visualized and when combined with adjacent elevation slices, a 3-D understanding of contaminant transport can be obtained. Figure 7 displays a vertical slice between the former Building 41 area and Allen Harbor, showing contamination in unsaturated areas (sources), contributions from several source areas, as well as current contaminant distribution of the coalesced CVOC plume. Effective application of the Color-Tec® screening process allowed for the use of real-time semiquantitative results to make field decisions that resulted in a much more comprehensive understanding of the extent of the CVOC plume. Not only was the CVOC plume more extensive than initially thought, but migration pathways were more complex. It is evident that the glaciated terrain is facilitating preferential flow in the more permeable lithologies. Additionally, several new source areas were identified that contribute to the coalesced CVOC plume. Color-Tec® Screening Cost Comparison Table 1 presents a cost comparison broken down by task for Color-Tec® screening versus fixed-base laboratory analysis. As presented in Table 1, the total cost of the Color-Tec® screening was approximately $15,000 (generally, a $10 per sample cost was realized throughout investigation) while the cost for the fixed-base laboratory would be significantly higher. Additionally, further cost savings are realized when considering data validation, data evaluation and preparation and review of a Data Package when fixed-base laboratory samples are collected. Therefore, Color-Tec® screening is significantly more cost efficient with minimal impact to data quality. Conclusions A comprehensive vertical profiling study was successfully performed in real-time using the relatively lowper-sample-cost ($10 per sample) Color-Tec® screening technology. The methodology was simple to use and results were quickly obtained. Significantly more soil samples were analyzed in the study than would have been possible using traditional fixed-base laboratory analyses. The study resulted in a more comprehensive understanding of Site 16 source areas and the nature and extent of the coalesced CVOC plume(s). Had this field screening method not been employed, it is likely that questions regarding source

areas and extent of contamination would remain unanswered. This work facilitated completion of the Remedial Investigation in 2009, with anticipated completion of the Feasibility Study in 2010 and Record of Decision in 2011.

Figure 1. NCBC Davisville Site Map.

Figure 2. Site 16 at NCBC Davisville.

Figure 3. Comparison of Color-Tec to Fixed Base Lab Results to LL Tube.

Figure 4. Comparison of Color-Tec to Fixed Base Lab Results to L Tube.

Figure 5. Comparison of Color-Tec to Fixed Base Lab Results to M Tube.

Figure 6. Total CVOC Conceptualized Isoconcentration Ranges for Soils, -15 to -25 feet msl.

Figure 7. Total CVOC Conceptualized Isoconcentration Ranges for Soils, Cross-Section C-C'.

Task

Color-Tec

Fixed-Base Laboratory

Equipment Costs

$1,500

None

Cost per Analysis

$10 to $20

$100

Time to Prepare Samples for Analysis (includes packing, COC preparation, etc.)

< 5 minutes (no packing and shipping necessary)

1 hour per 10 samples

Shipping/Transportation Costs

None

$75 per cooler

Total Estimated Costs for 1300 soil samples

$14500 to $27500

$131,500

Estimated time from sample collection to results available

approximately 10 minutes

No less than 10 to 14 business days

Table 1. Cost comparison of Color-Tec to fixed-base laboratory by Investigative Task.