PRELIMINARY DEVELOPMENT OF AN ADAPTIVE ASSESSMENT PROGRAM FOR OPERATING AQUIFER STORAGE AND RECOVERY (ASR) SITES JOHNSON C., TANCRETO A., MILLER J., LINKFIELD T., and BROWN C.*. University of North Florida, School of Engineering, Civil Engineering Department,
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[email protected] Keywords: Adaptive assessment, Aquifer, Framework Planning Abstract Aquifer storage and recovery (ASR) projects have been operating around the world for several decades in a variety of hydrogeologic regimes and supporting a myriad of water supply purposes. Unfortunately, recurring problems have continually arisen that could have been avoided if ASR lessons learned and improved adaptive assessment programs were instituted.The purpose of this paper is to expound upon the current planning methodologies for designing and operating a successful ASR system and to start the preliminary development of an appropriate adaptive assessment program for ASR projects. The first section of this document introduces five ASR sites with varying hydrogeological settings across the Unites States and details the major issues and creative solutions utilized at each site. The second section explains the current planning and operating methods. In the third section, recommendations are made for the initial development of an adaptive assessment protocol for the purposes of altering or enhancing the current planning methods in order to optimize the design and operation of each project.This is generally accomplished by collecting lessons learned from each project site so that in the future, recurring issues can be minimized. 1.
Introduction
The purpose of this paper is to perform a comparative review and analysis of multiple ASR site configurations and subsequent operating data to evaluate common traits, potential issues, and lessons learned for advancement in defining proper ASR planning processes and procedures. Currently there is minimal framework defining the proper design process and management practices of ASR projects. By reviewing past designs, implementation of recommended management strategies, and future improvement plans of ASR projects, a refinedoutline for improved ASR planning methodologies can be recommended. Data was analyzed in detail for fiveASR sites located within the United States, as denoted in Figure 1 by the orange markers.
*Figure not to scale
Figure 1.Five ASR project site locations.
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2.
Materials and Methods
The five ASR sites were selected based on the physical properties of each aquifer and basin, as well as the operational characteristics (including the intended use of the stored water bubble) and system-wide objectives which varied greatly between each ASR site. Data was collected from sources such as; annual reports, feasibility studies, performance evaluations, and previous management reports and operation plans. A brief summary of each site’s characteristics, background information, and operational history is provided in the following sections to aid in the revision of the existing ASR planning guidelines and to help in the formulation of an adaptive assessment program. 2.1
Las Posas Basin, Calleguas Municipal Water District
The Las Posas Basin ASR Project for Calleguas Municipal Water District stores surplus water within the confined Fox Canyon Aquifer (FCA) of the Eastern Management Sub-Area (EMSA) of Las Posas Groundwater Basin.The current project has been in-place for almost 20 years, includes 26 wells with a total recharge capacity of approximately 242,000 m3/day and was originally constructed to provide a reliable emergency water supply (Calleguas 2004).The project provides local storage within the FCAwhen other imported water supplies are limited. The FCA is located in a basin dominated by alternating layers of marine sands, marine gravels, and marine silts/clays (Pyne 1995; Brown 2005). The aquifer thickness ranges from 60 to 122 meters with a transmissivity ranging from 56 to 1,487 m2/day and an observed storage coefficient of 4 x 10-6 (Brown 2005). The project source comes from the existing state water project. Other recharge to the aquifer system originates from direct percolation, inflow from Oxnard Plain Basin, recharge from increased base flow in the form of wastewater discharges in Simi Valley and Moorpark, shallow dewatering discharges in Simi Valley, and urban runoff (Bondy et al. 2012). The various incoming base flows recharge the shallow alluvium surficial aquifer and underlying confined aquifers including the FCA. Over time, as pumping increased from the FCA, poorer quality recharge water was able to enter the aquifer from shallower aquifer zones (Bondy et al. 2012). Historically, well clogging has been a major issue (Brown 2005) but pro-active management has alleviated that problem, albeit at a higher maintenance cost. Currently, the main groundwater management issues identified include localized pumping depressions in the West Las Posas Basin, water quality including salinity management, and overall groundwater demand for the future. When in-lieu water deliveries are not being provided for the West Las Posas basin, declining water levels become a concern (Bachman 2012). These lowered water levels could induce poor water quality to flow or leak from surrounding areas and eventually cause increased pumping lifts, decreased production, and finally unsuitable well production (Bondy et al. 2012). Short (interim), medium, and long term strategies for management are currently planned to address all of the main issues of the Las Posas Basin ASR Project (Bondy et al. 2012). While the interim measures are in-place, LPUG will complete a number of critical planning tasks for the medium-term and long-term strategies. 2.2
Las Vegas Valley Water District
The Las Vegas Valley Water District (LVVWD) first began operating in 1989 and has injected nearly 435 million m3 of water since its inception (Landmeyer et al. 2000; personal communication from Erin Cole 2013). The purpose of the LVVWD ASR system is to provide water to the rapidly growing population during the peak summer months with the added benefit of groundwater level restoration. Treated water from the Colorado River is stored in the principal groundwater aquifer and recovered the during peak demand months. The well field is located mostly in the central and northwestern portions of the Las Vegas Valley. The ASR site is located above a vast variety of basin fill sediments. Early drilling logs indicate two general types of alluvial deposits; poorly sorted heterogeneous mixtures of boulders, gravel, sand, silt, and clay; and stringers of sorted gravel and sand deposits (Bernholtz et al. 1991). The aquifer is unconfined to semi-confined in nature with a highly variable transmissiv-
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ity ranging from 93 to almost 3,700 m2/day. A number of important historical and ongoing operational and management issues have been identified at the site. Historically, minor well clogging and in-situ production of disinfection by-products have been a major issue (Katzer & Brothers 1989; Brown 2005) but pro-active management has alleviated most of those problems. In-situ production of chlorine-based disinfection by-products has been a serious issue at several other ASR sites including one located in Lancaster, California (Fram et al. 2003). Currently, the project managers have been dealing with well clogging due to gas entrainment issues. In 2001 a study was conducted to determine the total dissolved gas (TDG) in the recovered water. The study concluded that ASR operations combined with temperature changes between recharge operations in the winter months and recovery operations in the summer months were the cause of TDG pressures in the aquifer reaching 202.65 kilopascals (kPa) with a composition of predominantly air. When water levels were lower, the design of the pump caused the water to cascade down the sides bringing air with it. Gas or air entrainment has long been identified as an injection well operational issue (Johnson 1981) yet the problem seems to reoccur with great frequency and has been noted at other ASR sites including one located in Salem, Oregon (Golder Associates 1996) and Highlands Ranch, Colorado (Bureau of Reclamation 1994; Pyne 1995). 2.3 Oak Creek The Oak Creek Water and Sewer Utility has operated the Oak Creek ASR site since about 2000 (Miller 2001) and has discontinued recharge and recovery actions. This site is located south of Milwaukee, Wisconsin which has historically relied on groundwater wells for fresh water, until a large water treatment facility was built to withdraw water from Lake Michigan, thus creating a need for alternative fresh water method. The purpose of theASR project was to take water from the treatment plant and inject it into the Cambrian-Ordovician aquifer and recover it during peak demand. Aquifer tests of the primarily sandstone storage zone revealed that the aquifer was fully confined with a transmissivity of 307 m2/day and a storage coefficient of 2 x 10-4. The ASR system utilized old emergency wells and other municipal wells which were converted to perform the specific function needed for the project. Historically, minor well clogging due to suspended solids and in-situ production of undesirable water quality parameters has been a major issue (Miller 2001; Brown 2005). Geochemical oxidation of pyrite was identified as one primary water quality problem through analysis of the change in concentration of manganese in the recovered water. Pilot tests of the ASR system revealed significant increases in dissolved manganese and iron in the observation well during the storage phase, which was likely the result of reductive dissolution of iron and manganese hydroxides in the aquifer (ASRTAG 2002). These levels exceeded the groundwater quality standards for those elements and therefore affected the overall feasibility of the project, which needed additional geochemical modeling to address. In 2011, the ASR site discontinued ASR operations due to geochemical-induced water quality problems. This continues to be a major issue for many other ASR project sites, including Lychett Minster, United Kingdom, Kissimmee River, Florida and Milwaukee, Wisconsin (Brown 2005). 2.4 San Antonio Water System The San Antonio Water System (SAWS) ASR project is very large project located outside of San Antonio, Texas. The SAWS ASR site was selected in 2004 after five potential aquifer locations were analyzed during a feasibility study due to its lower cost for recovery (personal communication from Mike Brinkman 2013). Water is taken from the Edwards aquifer and injected into the Carrizo-Wilcox aquifer during times of low water demand through a 225,000 m3/day capacity pipeline. At times of high water demand, water is taken from the Carrizo-Wilcox aquifer and treated before distribution. This is done through a treatment, storage, and pumping plant located on site. The Carrizo Wilcox aquifer consists of two geologic units, the Simsboro and Calvert Bluff Formations and the, overlying Carrizo Sand. These both form seven layers of deposition that were eroded from the Rocky Mountains. The mean transmissivity is approximately 28 m2/d and the specific storage has a mean of 4.5×10-6 (Mace et al. 2000).
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A number of important historical operational and management issues have been identified at the site. One of the main problems encountered was that the Carrizo-Wilcox aquifer was under the jurisdiction of several entities. The two entities, Evergreen Underwater Conservation District and SAWS, came to the agreement that SAWS had to begin recharge operations immediately, not after several years of pumping. It also stated that SAWS could pump 7,900,000 m3/yr based on the amount of land that the ASR field encompassed and up to the amount that would be stored. Possible direct impacts to nearby private well owners were another operational obstacle for the project. SAWS implemented mitigation programs ultimately agreeing to be responsible for compensating landowners for any adverse effects that the ASR operations would cause, such as extra drawdown caused by extended periods of recovery. Both of these measures ensure that SAWS, Evergreen, and the included landowners have a positive working relationship. The Bureau of Reclamation (1996) noted that ASR projects in Salt Lake City, Utah also struggled with similar issues. Another key management and operational issue identified by SAWS included the proximity to a brackish water supply. However, this seems manageable at the moment due to a confining unit that acts as a divider between the injection location and the brackish water (personal communication Mike Brinkman 2013). SAWS also has issues with finding optimal operating criteria such as determining when to start and stop ASR operations, defining a storage volume for the amount of water available for recover, and doing a better job at defining the factors that control the volume available. These include legal, regulatory, and water quality factors (Malcolm Pirnie Inc et al. 2013). 2.5
Tualatin Valley Water District and City of Beaverton
The Tualatin Valley Water District (TVWD) and the City of Beaverton were jointly interested in ASR as a new technology (Eaton 2004). From a municipal water production and ASR perspective, the Columbia River Basalt is the most important aquifer within the Tualatin Valley. As is common in most basalt aquifers, numerous fault zones have been identified within the study area, and these faults may have compartmentalized the regional basalt aquifer into sub-units. In Beaverton, recovery at the ASR site is limited to 95% of injection by state to cover potential basin losses through these faults. The northern portion of the Cooper Mountain basalt aquifer was selected as the site of the ASR pilot project because of its promising hydrogeologic conditions and existing large-capacity wells and conveyance facilities. Aquifer tests and borehole geophysical tests were completed and the results indicated that: the aquifer is relatively productive; the aquifer has a potentially large storage capacity; the aquifer may sustain injection rates of greater than 2.65 m3 per minute; the groundwater quality in the study area is good; and the existing wells are suitable for use as ASR wells. The aquifer storage zone is confined to semi-confined with a transmissivity of about 1,242 m2/day and storage coefficient of 1 x 10-4 (Brown 2005). Once ASR activities were implemented, no long-term decline in the static water level in the regional basalt aquifer attributable to ASR activities was noted, which strongly suggests; no appreciable net loss of stored water from the aquifer; no water quality standard exceedances were noted, and no adverse chemical reactions that potentially could clog the aquifer near the injection wells were observed. The water quality remained excellent during the recovery phase, which proves that Beaverton is a relatively successful ASR project. A number of important historical and ongoing operational and management issues have been identified at the site. These include high water levels in the aquifer during recharge events, partly due to increased flow in an area seep. Seeps, or areas where water reaches the surface from an underground aquifer, have considerable flooding risks, which can be problematic in urbanized environments, such as Beaverton. In order to aid in the interpretation of seep flows, it is beneficial to monitor the existing seeps both before and during recharge events (Brown 2005). Another issue at the Beaverton site was potential air entrainment. This can be attributed to a lack of downhole control valve in the first operational ASR well and since the static water level of the basalt aquifer is typically 61 meters below land surface. ASR No. 1 lacked a downhole con-
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trol valve or well liner due to its original installation date in 1945. In addition, rehabilitation of the well to add a downhole valve would be difficult due to well bore alignment issues and diameter constraints. The improper construction of early ASR wells contributed to injection turbulence which was one of the main operational issues encountered at the site. It was also found that periodic back flushing of the wells is critical to minimizing well clogging and upholding efficient ASR well operations (Brown 2005). The recovered water from the basalt aquifer experienced small increases in radon, iron, manganese, and trihalomethanes (THM); but all increases were well below drinking water standards. The recovered water also had elevated levels of dissolved oxygen on the first day of pumping, and this is attributed to the fact that the water close to the wellbore has had the shortest opportunity for microbial activity, and consequent reduction in dissolved oxygen. Another issue to note is that the recovery percentage was 85% of the 6.17 million m3 banked over the first six years of operation. The remaining 15% was not distributed evenly over the basin, resulting in a localized mound that influences local recharge performance negatively. 3.
Results
3.1
Current Planning and Implementation Methodologies
The importance of proper planning can largely influence the success of ASR while simultaneously reducing operational risk and uncertainty of variables including water quality, recharge and recovery volumes, cost, and other factors. Although there is not a set program standard regarding proper ASR technology use and implementation, previous research, journals and academic papers have been written on the topic. Pyne (1995) states that “although each ASR project tends to have important and site-specific issues that determine the nature and direction of activities, common themes emerging from these different projects form the basis of a recommended process for consideration at potential new ASR sites.” His broad approach includes a minimum of three phases; preliminary feasibility assessment and conceptual design, field investigation and test program, and recharge facilities expansion. 3.1.1 Phase 1 To begin phase 1 for any proposed ASR project, all objectives must be clearly defined and accepted by the parties involved. There are primary objectives for which the ASR is mainly designed to achieve and there also may be secondary objectives that are incorporated into the design for added benefit. The ASR site locations should be based on its potential to achieve all desired objectives and ability to incorporate ASR project features. Since the main purpose of most ASR wells is related to storage and recovery, a suitable storage zone for injection and recharge must be identified. This is an important step in the design process because it identifies the specific area where further research will be required and where potential facilities needed for the preliminary or final design of the ASR system should be located. Environmental, regulatory, and water rights issues should be evaluated in great detail during the conceptual design of the ASR site. It is common to find multiple users sharing the water stored within an ASR site and rights to water usage can become an issue since groundwater ownership is determined by each state’s laws. There are also environmental issues that can arise from the implementation of an ASR such as impacts to groundwater levels, water quality, and adjacent water bodies (Pyne 1995). In many states, ASR wells may require certain permitting and compliance to operate. Water quality guidelines for ASR systems may be applicable for certain countries, states, or environmental protection agencies. These guidelines may outline the minimum level of pretreatment required, minimum residence time, monitoring practices including the use of observation wells, maximum concentrations of contaminants in injected water, and others (Martin et al. 2002). Finally, an economic analysis should be conducted to determine the operating cost of the ASR to compare it to other water management alternatives. The water source(s) available for recharge, either through natural or artificial recharge processes
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should be carefully considered. Many issues with the injected water supply may arise such as variability in flow, water quality, and an increase or decrease of sources. If one of the main objectives is to recover water for reuse by a service area then water demand should be evaluated to ensure the supply will be reliable, treatment processes will be built to the proper capacity, and the volume of recovery will meet the current and future demand (Pyne 1995). Many water quality parameters for potable water must be addressed and proper design must ensure their management. This could include items such as conventional parameters, toxins, pathogens, disinfection by-products and emerging contaminants. According to Brown (2005), conventional parameters include total suspended solids (TSS), turbidity, alkalinity, color, chloride, sulfate and total dissolved solids (TDS). Pathogens and disinfection by-products are a common occurrence for any source water that has been treated using various methods of disinfection. Water may need to go through a pre-treatment process to meet regulatory requirements and improve overall water quality parameters before it is stored within the aquifer. One of the most important planning steps for ASR design is evaluating the hydrogeologic conditions within an aquifer to determine stratigraphy, aquifer properties, suitable storage zones, insitu water quality, hydraulic characteristics, mineralogy, geochemical properties, structures, boundaries, groundwater velocity and direction, contamination, and many others (Pyne 1995). The aquifer hydrogeology will control the distribution of the injected water within the aquifer storage zone and subsequent ASR recovery operations (Brown 2005). For useful storage to occur the ASR site should have lateral and horizontal boundaries without significant leakage (confined aquifers), which help increase the water levels and useful storage zone within the aquifer (Maliva et al. 2006). If the suitable storage zone is within an unconfined aquifer it should have a relatively high porosity so the stored water stays close to ASR well, have a setback buffer, and a substantial thickness of unsaturated area (Brown 2005). The effective porosity of the aquifer measures the available connected void spaces between sediment grains and directly influences groundwater circulation and flow velocity. The difference in horizontal hydraulic conductivity between the most and least conductive beds may be several orders of magnitude, and injected water will enter and move through the most conductive zones within the aquifer. Varying rates of hydraulic conductivity can cause changes in dispersivities in the longitudinal direction over two or three orders of magnitude (Brown 2005). The dispersivity and salinity of native storage zone water has also been found to be important variable for ASR performance because it can induce layered mixing and zones of diffusion (Maliva et al. 2006). 3.1.2 Phase 2 ASR program development for phase 2 concentrates mainly on field testing and test facilities. To begin, a test well may be constructed to perform pumping and injection testing. Pumping tests help establish the well and formation loss coefficients, well efficiency, and other hydraulic characteristics. Accurate hydraulic characteristics including flow rate, volume stored, water level and pressure within the well are essential to establishing projected ASR performance. It is important to test the water at multiple different stages of pumping or injection to determine if the quality is changing with time or if any plugging is occurring. If treatment processes are present, a zone may occur within a radius of tens of meters of the well in which ambient microbial activity is accelerated, geochemical changes are more prevalent and water changes occur (Pyne 2005). The appropriate amount and duration of ASR cycles is important because water quality results may show that leakage through a confining layer or a geochemical reaction is taking place. ASR testing cycles may need to be modified depending on the water quality difference between stored and native water, potential for geochemical reactions and storage time. Either before or during phase 2, hydrogeologic modeling may provide many additional benefits regarding the possible movement of the injected water within the aquifer or overall ASR projected performance. Modeling could include analytical methods, physical, or numerical calculations through the use of a computer. Modeling has increasingly become more refined and oftentimes results can provide details that aid in the planning process. This is especially true for aqui-
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fers that may have complex interactions between the ambient ground water and recharge water that may have a significant difference in salinity or water quality. 3.1.3 Phase 3 Phase 3 of the ASR Program development, ASR well field expansion, deals with ensuring the well field layout is designed to meet ASR purposes. The well field must be designed so the recharge and recovery flow rate distributions are equal. To prevent the flux of water from moving based on varying flow rates. This design is directly related to the well spacing since it influences the size of the volume of the stored water and subsequent recovery efficiency and optimization. Multiple wells at varying depths may also aid storage abilities by storing water in multiple aquifers, at varying depths, within the same site. The layout of the well field must also take into consideration the natural hydraulic gradient, density contrasts and groundwater velocity movement due to its influence on the movement of the stored water. The design of an ASR well is unique due to the specific functionality and purpose of an ASR system. An ASR well will have periods of wetting and drying during recharge and recovery periods which can lead to the formation of rust in steel castings. Rust may contribute to well clogging and therefore the casting materials of wells should be carefully selected. The screen and gravel pack must be designed so that it will keep the well casing from clogging due to the buildup of solids. The design is dependent on the surrounding geotechnical conditions, possible geochemical reactions that form solids, and potential microorganism growth. To help alleviate further geochemical or bacterial activity, associated plugging and air entrainment, cascading inside the well must be controlled. Cascading occurs when water cascades down the well causing air binding in the storage zone. 4.
Discussion
After researching and reviewing the current planning practices along with existing ASR sites, it is apparent that the problems are widespread and can be subdivided into three main categories; operational issues, institutional issues, and geochemical or geological issues. A majority of the major issues associated with each site are the direct result of an incomprehensive field investigation and planning which resulted in incomplete or improper design. While every site is different, more extensive field investigations will aid in designing a system that decreases the possibility for the common mistakes from reoccurring in a new site. The following sections detail the major issues encountered at each site, how they could have been avoided or minimized, and potential methods for alleviation by adopting an adaptive assessment mindset. 4.1
Operational Issues
4.1.1 Air Entrainment As was stated in Section 2.2 and 2.5 of this paper, the major issue encountered at the LVVWD ASR site and Beaverton site was entrained air. Entrained air is very undesirable for an aquifer and can lead to a variety of problems including; well clogging, reduction of transmissivity in the storage zone, as well as changes in oxidation-reduction potential, potentially leading to problems with geochemical reactions (Bouwer et al. 2008). A study was conducted by the LVVWD and determined that the majority of the air was getting into the system during ASR operations. One solution for reducing and/or eliminating the possibility of air getting trapped in the aquifer is to ensure the well is designed properly, in that the recharge conduits are always fully submerged (Brown 2005) or a downhole control valve is utilized. Issues related to well design can be eliminated in the field investigation and testing phase of the ASR design process. It is important to consider the changes in water level within the aquifer when designing the well system. During the field investigation, the existing groundwater level should be determined at each well point within the well field multiple times throughout the year. Variations in temperature along with draw down from other wells can cause fluctuations in the groundwater levels. Thus, it is
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important to note those fluctuations to ensure that the depth of the wellhead is enough to compensate. If proper design is not enough to eliminate the entrainment of air in the aquifer, the addition of downhole control valves can allow the well to maintain positive pressure within the injection tube. In turn, this will prevent water from cascading down the side of the well causing air entrainment and possible other issues as stated in section 3. 4.1.2 Injection Turbulence The main operational issue with the Beaverton site, as stated in section 2.5, was turbulence during injection. Injection turbulence can ultimately lead to backpressure, head losses, and turbidity. This issue was attributed to the fact that old production wells had not been properly constructed for ASR injection, which resulted in performance losses and special operation steps. These old wells were open hole wells which are not suitable for ASR projects. In order to accommodate for less turbulence, the open sections of the old wells should be lined, and any new wells should be constructed with stainless steel, or some material of similar quality, casing and wire wrap screen. It also must be noted during construction that the borehole diameter must be large enough to accommodate not only the potential volume of water being injected, but also the pump, downhole control valve, control lines, transducer sounding tube, and water level sounding tube. Inadequate borehole diameters can lead to compressing of these items and can negatively affect injection turbulence and can also lead to backpressure, head losses, and turbidity (AWWA 2008). 4.2
Geochemical and Geological Issues
4.2.1 Salinity The main issue within the Las Posas basin is water quality due the higher salt concentrates from the recharge of the base flow due to the leakage from the overlying aquifer and the surface water. For the San Antonio ASR project, the site is close to a brackish water supply but monitoring at the site will ensure there is not a significant amount of leakage of the poor quality brackish water into the ASR storage zone through the confining unit. As explained in section 3, salinity can have many adverse effects on the performance of the ASR recovery and performance. Also, high salinity may require the designer to select stainless steel well casing at a greater overall cost to the project. At the Las Posas site, more intense field investigations may have identified the higher salt concentrations within the shallow aquifer and the geological characteristics of the confining layer which has allowed leakage to occur. Since the leakage from the shallow aquifer is a main source of recharge for Las Posas, planning for an increase in poor water quality should have been further analyzed. For San Antonio, defining the possible leakage through confining unit due to pumping rates is important to estimate and prepare for to ensure excessive drawdown does not promote leakage. In general, both current and future source water quality for injection must be considered during the design phase to ensure that treatment facilities are minimized to the extent practical and costs kept as low as possible. Methods of remediation for salinity include treatment processes for desalting the water, mixing water of higher quality or changing the source water, and placing injection wells in a formation that can confine areas of higher or lower quality. 4.2.2 Well Clogging Well clogging has been an issue for injection wells for about 3 decades (Johnson 1981; Bichara 1986), yet it seems to be an ongoing operational issue. As was stated in Sections 2.1, 2.3, and 2.4, a major issue encountered at the Las Posas Calleguas, CA, Oak Creek, WI, and San Antonio, TX sites was well clogging. Well clogging is one of the most common issues encountered during ASR operation. The more common types of clogging that occur in ASR wells are; deposition of total suspended solids (TSS) from the recharge source water, biological growth, geochemical reactions, and particle rearrangement in the aquifer materials adjacent to the well (Bouwer et al. 2008). A buildup of particles on the gravel pack, the borehole wall, or in the formation immediately surrounding the borehole wall can cause a substantial decrease in pumping
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efficiency. Minimizing TSS concentrations to less than 5 mg/L in the recharge water typically helps prevent serious well clogging. Issues related to well clogging can also be mitigated during the field investigation, testing phase of ASR planning, and during a well-planned monitoring effort. As was previously stated, air entrainment and cascading can also promote clogging of a well. One of the first field tests that should occur is the test of source water compatibility. Introducing water into the system that reacts adversely with the ambient groundwater and hydrogeologic properties can cause geochemical reactions and solids to precipitate or biological clogging to occur. While these tests are commonly performed for potential ASR sites, it is possible water chemistry and/or hydrogeological properties vary between well sites. Therefore extensive testing for each well site should be conducted to ensure the entire system functions successfully. Biological or microbial clogging may occur related to the treatment processes selected for the site (e.g. if TSS or excess color is not removed from source water). Finally, particles from the surrounding aquifer may migrate during the recharge and recovery phase. As stated earlier, the screen and gravel pack must be designed properly to alleviate excessive particle buildup or to keep formation particles from entering the well. A common solution for well clogging that is implemented by many successful ASR sites is to backflush the wells periodically to prevent buildup. Often times, chlorinated water is used to breakdown the biological buildup as well as dislodge the fine particles (Brown 2005). 4.3
Institutional Issues
4.3.1 Excessive Drawdown or Pumping Depressions The Las Posas Basin has significant issues in the western portion of the basin due to a hydraulic fault that hinders groundwater flow from reaching this area. This eventually causes a decline or drawdown in hydraulic head within the aquifer, which will continue until the rate of flow out of the well equals the amount of water supplied through recharge and injection. Therefore, wells within basins having these issues should be monitored closely and possible caps on pumping may need to be implemented. Also shifting pumping locations to address the declining water levels based on the injection/extraction cycles may be needed. In-lieu deliveries or additional conveyance options to basins may also help raised the ambient ground water elevations so pumping depressions are less severe. A drawdown monitoring program should be implemented to control and mediate excessive drawdown. Similar issues with possible excessive drawdown have also been encountered at the SAWS ASR site but the plan of remediation includes financially compensating the other well users in the area. 4.3.2 Current and Future Demand One of the most important aspects of all ASR projects is the ability to provide adequate storage and supply to meet the current and future demand. This must be analyzed early in the design phase. With fresh water sources being depleted, ensuring future demand is met will continue to keep ASR projects more economically feasible than many other alternatives. 5.
Acknowledgements
We would like to thank our contacts at each of the ASR sites mentioned in this paper. Thank you Erin Cole, LVVWD and Bryan Bondy, Calleguas Municipal Water District, for providing us with such an abundance of information and allowing Mary Johnson to tour the ASR sites in your areas. Thank you Jen Woody, Oregon Water Resources Department, and Greg Even, Department of Public Works Los Angeles for the information regarding the Beaverton, Oregon ASR site. Finally thank you to Monica Autrey of Destin Water Users, Inc. 6.
References
Aquifer Storage Recovery Technical Advisory Group(ASRTAG). (2002). A Review of Aquifer Storage Recovery Techniques.
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Bachman, S., (2012) Las Posas Basin ASR Project Annual Report 2007-2010 Bernholtz, A., Brothers, K., Katzer, T. (1991). Analyses of aquifer responses due tocontinued artificial recharge of treated Colorado river water, lavages valley, Clark county, Nevada. Arizona Hydrological Society Fourth Annual Symposium Proceedings. Francisco Grande Resort, Casa Grande, September 12-13. Bichara, A.F., (1986). Clogging of recharge wells by suspended solids. Journal ofIrrigation and Drainage Engineering, 112(3):210-225. Bondy, B., Bachman, S., Graumlich, H., (2012) Los Posas Basin-Specific Groundwater Management Plan, Final Draft. Bouwer. H, Pyne. D, Brown, J., St Germain, D., Morris, T., Brown, C., Dillon, P., Rycus, M. (2008). Design, operation, and maintenance for sustainable underground storage facilities. AWWA Research Foundation, Denver, CO, USA. Brown, C. (2005). Planning decision framework for brackish water aquifer, storage and recovery (ASR) projects, Ph.D. Dissertation, University of Florida, USA. Bureau of Reclamation, (1994). Final report highline well field asr project. United States Bureau of Reclamation, Denver, Colorado, 325 p. Bureau of Reclamation, (1996). Summary report, southeast salt lake county artificial groundwater recharge demonstration project.United States Bureau ofReclamation, Denver, Colorado, 15 p. Calleguas Municipal Water District, (2004). Las posas basin asr project, summary memo, Thousand Oaks, California, 4 p. Martin, R., Dillion, P. (2002) ASRfuture directions for south Australia. Department of Water, Land and Biodiversity Conservation. Eaton, Larry, (2004). Email Communication. Beaverton ASR Site Executive Summary Information, 4 p. Fram, M.S., Bergamaschi, B.A., Goodwin, K.D., Fujii, R., Clark, J.F. (2003). Processesaffecting the THM Concentrations Associated with the Third injection, Storage, and recovery test at Lancaster, Antelope Valley, California, March 1998through April 1999. United States Geological Survey Water Resources Investigations Report 03-4062, Sacramento, CA, 68 p. Johnson, A.I., (1981). Some factors contributing to decreased well efficiency during fluid injection of water for subsurface injection. ASTM STP 735, 1: 89-100. Katzer, T. and K. Brothers, (1989). Artificial recharge in lasvegas valley, ClarkCounty, Nevada. Ground Water, 27(1):50-56. Landmeyer, J.E., Bradley, P.M., Thomas, J.M. (2000). Biodegradation of disinfection byproducts as a potential removal process during ASR. Journal of the AWRA, 36(4):861-867. Mace, R. E., Smyth, R. C., Xu, L., Liang, J. (2000). Transmissivity, Hydraulic conductivity, and storativity of the carrizo-wilcox aquifer in Texas. Prepared for Texas Water Development Board. Austin, Texas, 7 p. Malcolm Pirnie, Inc, ASR Systems LLC, Jackson, Sjoberg, McCarthy & Wilson, LLP, (2011) Anassessment of ASR in Texas. Prepared for Texas Water Development Board, Austin, Texas, 23 p. Maliva, R.G., Guo, W., Missimer, T. (2006) ASR: recent hydrogeological advances and system performance, Water Environment Federation, Dec 2006. Miller, T.J., (2001). ASR of drinking water using the cambrian-ordovician aquifer in Wisconsin. Cooperative report prepared for the oak creek water and sewer utility and the AWWA research foundation, published by the AWWA research foundation, Denver, Colorado, 349 pp. Pyne, R.D.G., (1995). Groundwater recharge and wells: a guide to ASR. Lewis Publishers, Boca Raton, Florida, 375 p. Wisconsin Groundwater Coordinating Council, (2013).ASR. Prepared for the Legislature, 1 p. Pyne, R.D.G., (2005). ASR issues and concepts, St. Johns river water management district special publication; St. Johns River Water Management District. Jacksonville, Florida.
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