October 17, 2000
The following is the U.S. Army Corps of Engineers (USACE)/South Florida Water Management District (SFWMD) preliminary response to written questions posed by the CROGEE ASR Subcommittee. The response is formatted such that the question is repeated, followed by the USACE/SFWMD response in bold. We hope that providing these comments ahead of the October 19, 2000 meeting will clarify some issues and guide the discussions at the meeting.
Topic I - Regional hydrogeologic framework issues (Note that this is primarily portions of Issue Team items 2 and 4)
Questions that are likely to arise in some form:
What are the main sources of uncertainty with respect to the regional hydrogeologic framework?
Perhaps the greatest source of uncertainty is the fact that the existing hydrogeologic data have not yet been compiled and evaluated. Regional hydrogeologic investigations conducted by the USGS as part of its Regional Aquifer System Analysis (RASA) program, as well as the Florida Geological Survey's (FGS's) evaluation of the Hawthorn Group (Scott, 1988) provide solid evidence as to the lateral extent and continuity of the Floridan Aquifer System (FAS) and the overlying Hawthorn confining unit.
Recognizing the importance of an understanding of regional issues, and the budget limitations of the pilot projects, USACE/SFWMD are now proposing to allocate funds to conduct a Regional Study in parallel with the pilot projects. The scope of the Regional Study is not yet defined, but will be refined based on CROGEE comments.
Do the pilot projects include the necessary studies to resolve these uncertainties and fill in the data gaps to characterize the properties and regional extent of possible injection zones as well as properties and extent of other significant hydrostratigraphic units (e.g. aquifers that are used for drinking water supply, confining units that would separate these from the injection zones or separate ASR injection zones from intervals used for waste injection)?
Development of the regional hydrogeologic framework will be one of the first tasks conducted. Filling in data gaps with additional wells is a logical but costly task, and we believe beyond the scope of the pilot projects. If needed, additional wells could be installed as part of the recently proposed Regional Study.
Note that we propose to install three (3) monitor wells at geographically dispersed locations around Lake Okeechobee to get some site-specific data geared toward evaluation of the
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Page 30 Appendix C Questions sent to the SFWMD prior to the workshop, and its responses October 17, 2000 The following is the U.S. Army Corps of Engineers (USACE)/South Florida Water Management District (SFWMD) preliminary response to written questions posed by the CROGEE ASR Subcommittee. The response is formatted such that the question is repeated, followed by the USACE/SFWMD response in bold. We hope that providing these comments ahead of the October 19, 2000 meeting will clarify some issues and guide the discussions at the meeting. Topic I - Regional hydrogeologic framework issues (Note that this is primarily portions of Issue Team items 2 and 4) Questions that are likely to arise in some form: What are the main sources of uncertainty with respect to the regional hydrogeologic framework? Perhaps the greatest source of uncertainty is the fact that the existing hydrogeologic data have not yet been compiled and evaluated. Regional hydrogeologic investigations conducted by the USGS as part of its Regional Aquifer System Analysis (RASA) program, as well as the Florida Geological Survey's (FGS's) evaluation of the Hawthorn Group (Scott, 1988) provide solid evidence as to the lateral extent and continuity of the Floridan Aquifer System (FAS) and the overlying Hawthorn confining unit. Recognizing the importance of an understanding of regional issues, and the budget limitations of the pilot projects, USACE/SFWMD are now proposing to allocate funds to conduct a Regional Study in parallel with the pilot projects. The scope of the Regional Study is not yet defined, but will be refined based on CROGEE comments. Do the pilot projects include the necessary studies to resolve these uncertainties and fill in the data gaps to characterize the properties and regional extent of possible injection zones as well as properties and extent of other significant hydrostratigraphic units (e.g. aquifers that are used for drinking water supply, confining units that would separate these from the injection zones or separate ASR injection zones from intervals used for waste injection)? Development of the regional hydrogeologic framework will be one of the first tasks conducted. Filling in data gaps with additional wells is a logical but costly task, and we believe beyond the scope of the pilot projects. If needed, additional wells could be installed as part of the recently proposed Regional Study. Note that we propose to install three (3) monitor wells at geographically dispersed locations around Lake Okeechobee to get some site-specific data geared toward evaluation of the
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Page 31 potential for ASR zones and confining units. This task will occur simultaneously with development of the hydrogeologic literature search. Following this task, three (3) large-diameter exploratory wells will be permitted and installed to better assess hydrogeologic characteristics, evaluate hydraulic capacity, and result in selection of the target ASR storage zone. Will the pilot projects be adequate to develop a regional conceptual model suitable for translation into the numerical model that is intended to provide a preliminary assessment of regional effects of the ASR system? Recognizing the importance of an understanding of regional issues, and the budget limitations of the pilot projects, USACE/SFWMD are now proposing to allocate funds to conduct a Regional Study in parallel with the pilot projects. The scope of the Regional Study is not yet defined, but will be refined based on CROGEE comments. The scope of the Regional Study will include development of a conceptual model from several sources including: 1. Hydrogeologic literature search 2. Automation of 30 FAS wells to assist in model calibration 3. Hydrogeologic data from the 3 new monitor wells noted above 4. Hydrogeologic data from the 3 new large-diameter exploratory wells We believe these data are sufficient to develop a regional numerical model, but are aware that one can always make an argument that more data are needed. If the pilot projects will not provide all of the necessary information to characterize the regional framework and to allow development of a numerical model, what other studies will be going on in parallel to provide the necessary information? Recognizing the importance of an understanding of regional issues, and the budget limitations of the pilot projects, USACE/SFWMD are now proposing to allocate funds to conduct a Regional Study in parallel with the pilot projects. The scope of the Regional Study is not yet defined, but will be refined based on CROGEE comments. What information is available, or what analysis has been done, to estimate changes to the regional flow system due to the aggregate head-buildup and drawdown associated with the proposed projects? No analysis has been conducted to date. Anecdotal data from existing FAS and ASR Wellfields (Town of Jupiter, Cocoa, Peace River) indicate that intense pressure build-up and drawdown has not occurred. We will document these and other data during the plan formulation process. Ultimately, the proposed regional modeling effort will best allow us to address this question. How did selection of the proposed locations for exploratory wells, pilot ASR wells and monitor wells relate to locations that are likely to provide the necessary constraints for characterizing the regional framework? The proposed sites for the 3 exploratory wells (i.e., at the confluence of the Caloosahatchee, Kissimmee, and St. Lucie Rivers with Lake Okeechobee) were selected for two primary reasons. First, these sites are known to possess a great amount of water availability. Of course, we know that Lake Okeechobee has available water, but conversations with Lake experts indicate that
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Page 32 water quality can vary substantially between the Lake and rivers/tributaries, depending on seasonal and weather conditions. The intent here is to allow for ASR recharge with the best quality water when it is available, be it Lake Okeechobee or its tributaries/estuaries. Second, we must discharge aquifer water (e.g., reverse-air drilling, well development, packer test, specific capacity test, aquifer performance test, etc.) to facilitate well construction and testing. This must be accomplished in compliance with the required National Pollutant Discharge Elimination System (NPDES) permits. Often times, it is difficult to meet the NPDES permit requirements (e.g., 800-meter mixing zone for conductivity, no exceedance of 29 NTUs above background turbidity) unless a flowing water body is close by. Thus, the proposed monitor and exploratory wells are located at these major tributaries/estuaries. These reasons for site selection, however, do not preclude the ability nor minimize the importance of gathering useful regional hydrogeologic information. In fact, we believe it prudent to begin the regional characterization at those sites where ASR systems are most likely to be situated. Could ASR exploratory wells, downsized, be used in a hydrostratigraphy mode and later converted to ASR monitor wells? Yes, but it is our intent to re-permit these exploratory wells as functional ASR wells, depending on source-water quality. How will results of geophysical logging and hydraulic tests at the proposed exploratory well locations be extrapolated to provide information on hydraulic properties over the regional scale? By comparing the regional hydrogeologic data with that from the monitor wells and exploratory wells, we intend to develop a conceptual model of the hydrogeologic system. Ultimately, this will be used as the building block for the numerical model with which we will attempt to address regional issues raised by the ASR Issue Team and/or CROGEE. If the results at sites that have been selected for exploratory wells do not provide the information necessary to constrain a regional hydrogeologic conceptual model, will there be funds available to construct additional exploratory wells in other locations? To clarify, the data from the 3 monitor wells and the 3 exploratory wells are insufficient in and of themselves to constrain a regional hydrogeologic conceptual model. These new data must be used in conjunction with the regional hydrogeologic information to develop the conceptual model. As stated above, there are insufficient funds in the pilot projects at this time to install additional monitor wells apart from those previously mentioned to fill regional data gaps. Of course, it is difficult to predict the myriad of circumstances that might change this current plan. Note that the CERP process goes to painstaking lengths to allow for mid-course corrections to the plan based on newly acquired information, so we cannot by definition rule this task out. Realistically, project elements other than hydrogeologic investigations (e.g., regulatory, design, construction, testing) currently constrain the pilot project funds available for additional wells above those mentioned herein. The newly proposed Regional Study may allocate funds for additional wells if required.
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Page 33 Who will undertake the task of developing the regional flow model and running simulations to assess regional effects? Are those who will be involved in model development going to be involved in the planning of data collection activities in order to assure that the necessary data are available to constrain conceptual and numerical models? At this time, it is envisioned that the USACE will take the lead on implementing the regional groundwater model, with assistance from the SFWMD and the other members of the PDT. USACE options to implement this task include conducting these services in-house, working with the USGS, or out-sourcing the work to architectural-engineering (A/E) firms (as mandated for 40% of their work by Congress). Yes, the model developers will have early input to the data collection activities to ensure that model data needs are met. Topic II - Water quality issues, regional and local (Note that this topic includes Issue Team items 1, 5 and 6) Questions that are likely to arise in some form: Of the possibilities noted in the various planning documents, which of the proposed sources of water for injection in the Lake Okeechobee and Hillsboro ASR systems are believe to be the most likely? For the Lake Okeechobee ASR Pilot Project, certainly the Lake itself in conjunction with the major tributaries/estuaries (e.g., Caloosahatchee, Kissimmee, and St. Lucie Rivers) are the most likely sources, given our previous response. For the Western Hillsboro ASR Pilot Project, the Hillsboro Canal and horizontal wells adjacent to the proposed pilot impoundment (to capture seepage) are the most likely sources. How will the regulatory concerns associated with injection of these source waters be addressed in the pilot studies? As the pilot project PMP indicates, two primary tasks are geared towards addressing regulatory issues. First, the source-water quality characterization program attempts to characterize spatial and temporal variability of source water prior to ASR recharge. This is required to obtain an Underground Injection Control (UIC) permit. In addition, it will help determine the parameter list for recovered water. Second, a study to evaluate the fate of microorganisms is included to evaluate the potential for in-situ aquifer conditions to neutralize these microorganisms. It is hoped that results of this study will indicate that microorganisms die-off within the aquifer, precluding the need for expensive pre-treatment (i.e., ultrafiltration) that could result in a project savings of between $250 to $400 million for CERP ASR. What is known and what needs to be learned about source water quality, including possible temporal variations? Basic information about source (surface) water is available, but not to the level required for permits, nor an in-depth understanding of potential geochemical reactions that might occur when it is mixed with aquifer water. As you might expect, much of the data are focused on the phosphorous issue. In general, surface water such as Lake Okeechobee and its tributaries/estuaries has a high organic content. Western portions of the Lake appear to have the best water quality. In addition, there appears to be an inverse relationship between turbidity and
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Page 34 algae content, both potentially problematic issues with respect to potential plugging of ASR zones. The USGS and SFWMD entered into a cooperative program last year to begin characterizing surface and aquifer water quality, focusing on parameters useful for geochemical modeling purposes. The proposed source-water quality characterization program attempts to fully characterize water quality and understand temporal variability by conducting sampling seasonally for at least one year, and storm event sampling. Pre-treatment systems must be designed to accommodate temporal changes in water quality, especially during storm events when presumably the greatest volumes of water are available. Which of the parameters in the water quality list are important to address regulatory concerns? Which of the parameters in the water quality list are important to address anticipated differences between source waters and ambient groundwater in potential injection zones? Obviously, the primary and secondary drinking water standards (DWS) are by definition geared towards regulatory concerns, though not exclusively. In addition, some parameters not on the DWS list (e.g., microorganisms) are focused on regulatory issues. Parameters focused on mixing and water-rock interactions include basic cations/anions, chlorides, total dissolved solids, pH, arsenic, radionuclides, and isotopes. What is known and what needs to be learned about ambient water quality in potential injection zones, including spatial variations in water quality over the region that will be affected by the ASR systems? Various hydrogeologic reports attempt to characterize the spatial variability of groundwater within the Floridan aquifer system (FAS). This information will be compiled as part of the hydrogeologic literature search. In addition, limited water quality sampling and analysis of existing FAS wells for basic parameters – principally chlorides, pH, TDS, conductivity, etc. – are conducted on select wells as part of FDEP's ambient water quality monitoring program, partially implemented by SFWMD. Finally, ambient water quality will also be sampled and analyzed from those FAS monitor wells and exploratory ASR wells installed as part of the pilot projects. In general, ambient water quality appears to freshen as one proceeds northward within a given hydrogeologic unit, ultimately becoming fresh in the Orlando area. Vertically, water quality gradually deteriorates downward to approximately 1,800 feet in South Florida, where a saltwater interface is encountered. There have been documented exceptions to this rule within zones of the upper FAS, but always at depths above 1,800 feet. Will the pilot studies provide the necessary data to adequately characterize source water quality and ambient water quality in the injection zones, including temporal and spatial variability? Yes, we believe that the background- and source-water quality characterization developed will sufficiently characterize these waters to facilitate the pilot projects, as well provide information for regional evaluation of the proposed full-scale ASR implementation.
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Page 35 If the pilot studies will not provide all the data that may be needed, what additional studies are planned to fill the gaps? Development of the Regional Study scope of work might identify other studies, but this has not been conducted to date. What is known and what needs to be learned about potential water quality changes induced by mixing of source waters and ambient groundwater in the injection zones? The Florida Geological Survey (FGS) has conducted studies to indicate that leaching of arsenic and radionuclides from the carbonate aquifer matrix has occurred in the Tampa Bay area, relatively close to the Lake Okeechobee ASR Pilot Projects. It is postulated that the influx of highly oxygenated source water within the anaerobic environment of the FAS results in a redox potential conducive to leaching of these bound constituents into solution. Some evidence suggests that this phenomenon decreases over time, but more study on this issue is needed. We intend to rely on the Tampa experiences (and other existing ASR sites, if applicable) to better understand this issue. Given the timeframe to permit/design/construct the ASR Pilot Facilities, we must rely on existing ASR facilities to answer some of these questions near term. On a positive note, many ASR facilities have been operating in the state of Florida – indeed, globally -- with no observed water quality concerns other than those mentioned above. ASR sites with water quality issues have been observed in granular aquifers, where the potential for plugging due to formation and precipitation of iron oxyhydroxides and manganese exists. Fortunately, the carbonate, solution-riddled aquifers that we propose for ASR storage have been shown to result in little concern for plugging if operated and maintained properly. What is known and what needs to be learned about potential water quality changes that may occur due to water-rock interactions? See previous comment Will the geochemical modeling proposed as part of the pilot studies be adequate to predict water quality changes due to mixing and water-rock interactions? Are the necessary thermodynamic and kinetic data for the geochemical modeling readily available, especially for minor, trace, and organic constituents? Yes, we believe our approach adequately addresses the question about mixing and water-rock interactions. The entity responsible for geochemical modeling will ensure that data needs are identified up front to facilitate geochemical modeling. Note that the USGS and SFWMD previously entered into a cooperative agreement to collect background information that should facilitate geochemical modeling. Note also that geochemical modeling was conducted as part of SFWMD's ASR demonstration project (CH2M HILL, 1989) near Taylor Creek/Nubbin Slough on the north side of the Lake, which predicted no significant adverse chemical reactions that would preclude ASR storage. Will the cycle testing proposed as part of the pilot studies be conducted over appropriate time scales and using appropriate water sources to provide a test of the predictions of the geochemical modeling?
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Page 36 Yes, though cycle testing may not be completed in time for decisions on whether to proceed with the next phase of ASR implementation on a regional scale, as contained in the Project Implementation Report (PIR) phase of the project. If observations of water quality changes during cycle testing do not match predictions of the geochemical modeling, will additional studies be undertaken to resolve discrepancies? Yes, though this will occur during the Project Implementation Report (PIR) phase, following completion of the ASR Pilot Projects. What are the direct receptors (e.g. Lake Okeechobee, municipal water supply, canals) and indirect receptors (e.g. water conservation areas and portions of the Everglades that receive flow from the Lake Okeechobee area) for water recovered from the ASR systems at Lake Okeechobee and Hillsboro? The example receptors embedded in your question are the primary receptors. What is known and what needs to be learned about water quality requirements of the receptors for water recovered from the ASR systems? From a permitting perspective, the environmental requirements include complying the applicable Class I or Class III water quality criteria from NPDES permits. From a municipal perspective, water recovered from ASR systems to Lake Okeechobee must meet Class I (i.e., drinking water) criteria, and also not result in water quality changes such that the water cannot be treated at municipal water treatment plants that serve Glades-area residents. Will the pilot studies provide the necessary information to evaluate the suitability of recovered water for its intended receptors? Yes, a sampling and analysis program for water recovered from ASR systems will be developed and implemented to address these concerns. Note that the details of this plan necessarily require that we await the results of the source-water quality characterization program to ensure that parameters of concern are addressed. If the pilot studies will not provide the information needed to assess suitability of recovered water for the intended receptors, what other studies are planned to fill the gaps? Development of the Regional Study scope of work might identify other studies, but this has not been conducted to date. Topic III – Local performance/feasibility issues (Note that this topic includes Issue Team items 3, 6 and 7) Questions that are likely to arise in some form: What is known and what needs to be learned about rock properties in potential storage zones and adjacent confining units in order to estimate critical fracture pressures?
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Page 37 Some data exists about rock properties from cores analyzed at other well sites. In addition, preliminary review of rock fracturing literature review indicates that approximately one psi of pressure per foot of overburden has been empirically shown to be the critical pressure for rock fracturing. Assuming a depth of 1,000 feet, it is doubtful that we would generate 1,000 psi of pressure to result in fracturing of the overlying Hawthorn confining unit. Will the pilot studies provide the necessary data on rock properties for this analysis? If not, what additional studies are planned to fill the gaps? Cores will be obtained from the overlying confining units and from the ASR storage zone for laboratory analysis and determination of petrophysical properties. Will a regional scale flow model of ASR system operation be adequate to predict local pressure buildups in the vicinity of injection wells for the purpose of evaluating fracture potential? If not, what other types of modeling will be required? The current version of the pilot project PMP outlines a plan to conduct a desktop analysis using analytical techniques perfected in the oil industry to evaluate induced fracture potential from the proposed regional ASR system. The regional modeling effort should yield pressure information which can be compared with empirical data from the literature (and laboratory analysis of cores) to further evaluate induced fracture potential. If there are other techniques that CROGEE is aware of, we'd be happy to consider their use. What is known and what needs to be learned about the potential to inject water in the ASR system at the rates anticipated by the Restudy? The 5 million gallon per day (mgd) capacity has been demonstrated at two sites (i.e., Miami-Dade Water and Sewer Department West and Southwest ASR Wellfields). Other sites (i.e., West Palm Beach, Western Hillsboro, and Broward County) have demonstrated the hydraulic capacity to recharge water at these rates. We need to learn if the Lake Okeechobee area has an ASR zone with a hydraulic capacity to recharge/recover at this rate. The 3 large-diameter exploratory wells are the first step in addressing this question. From the broader perspective, admittedly little is known about the ability of the FAS to recharge/recover cumulative flow rates (1,665 mgd) proposed in the CERP. A combination of ground-truthing the 5-mgd per-well capacity in conjunction with the regional groundwater modeling should help answer this important question. More philosophically, 50 years ago it might also have seemed unlikely that the FAS could have supported current withdrawals, although admittedly with environmental and resource implications. What is known and what needs to be learned about the potential to recover the required volumes of water with suitable quality for the intended receptors? Little is known about the ability to of the proposed regional ASR systems to recover the volumes of water needed to meet future environmental, urban, and agricultural demands of South Florida, hence the need to conduct pilot studies. Assuming successful results of the pilot projects, and subsequent step-wise implementation of regional ASR, more will be learned to evaluate the ability of regional ASR systems to meet water quality and quantity needs of intended receptors/users.
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Page 38 How is “efficiency” of recovery going to be quantified in the pilot studies? Are different definitions of “efficiency” required depending on the intended receptors of the water? Recovery efficiency is a term open to interpretation, depending on the needs of the end user. Traditionally, it is defined as the amount of water recovered – given a pre-determined upper water quality limit above which water will not be recovered – divided by the volume of water stored. The recovery efficiency term can be skewed because the amount of water left in the zone has an effect of the recovery efficiency of the next cycle. While we will collect data to evaluate recovery efficiency, we prefer to use the term recoverability; that is, is the water available when we need it to meet demands. If so, the recovery efficiency term becomes less important. Will the cycle testing conducted in the pilot studies be at appropriate rates and cover appropriate times scales to allow extrapolation of results for the purpose of estimating the recovery efficiency for long term operation under the conditions anticipated in the Restudy? Cycle testing will be conducted to evaluate appropriate recovery rates. Extrapolation of recovery efficiencies may be more problematic if the traditional approach of building a target storage volume (TSV) over successive cycles is employed. Some evidence suggests that the well-known increase in recovery efficiency over successive cycles can be replicated by storing available water early in the testing program, with little water recovered to establish the subject TSV. It is recommended that when we get to the testing phase, we explore this technique given the experiences at other operational ASR sites. Topic IV – Other issues, left-over issues, “open mike” Questions that are likely to arise in some form: What additional problems, besides those of the ASR Issue Team, have been identified by the SFWMD to date? The study to evaluate the fate of microorganisms in aquifers mentioned previously was not specifically raised by the ASR Issue Team, but looms large with respect to the permittability of the proposed ASR systems. Do the pilot projects address any of these additional problems? Yes, a study to evaluate the fate of microorganisms is one of the first tasks to be conducted. What are the principles that govern your proposed distribution of funding, and timing, of regional studies vs. site testing? Good question. The CERP document (April 1999) does not provide many details about the ASR Pilot Projects, an artifact of preparing a typical 5-year feasibility study within the 2-year timeframe mandated by Congress. Having said that, the $19 million figure for Lake Okeechobee $8 million figure for Western Hillsboro, and $6 million figure for Caloosahatchee were crudely based on estimates for a given number of ASR systems, assuming approximately $2 million per system. Unfortunately, there were no specific funding streams to answer some of the regional questions raised by the ASR Issue Team (July 1999, note the date for CERP document). In the
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Page 39 current version of the PMPs, we've attempted to strike the appropriate balance between permitting/designing/ constructing/testing functional ASR systems, and answering regional questions. We think we've achieved that daunting task with our current plan, though the proposed Regional Study will now result in additional funds to conduct regional investigations. Two underlying themes emerged from our participation in the ASR Issue Team not documented in their report. First, locating all ASR wells in one geographic location (e.g., the west side of Lake Okeechobee) does not answer a fundamental question; that is, does ASR work in geographically dispersed areas around the Lake. The corollary is, it would be difficult to recommend the next phase of ASR implementation (e.g., a 30-well system) in a geographic area that doesn't have a pilot facility in place and successfully operating. The second theme was, “We know that single-well systems work, we want to know how multiple wells interact with each other.” This begins to answer the question, “What is the optimum spacing between ASR wells so that coalesced “bubbles” of freshwater result in an underground reservoir of fresh water.” These three paragraphs are a long-winded justification for six (6) ASR wells, three in geographically dispersed locations and three at an individual ASR “cluster” for the Lake Okeechobee ASR system. Budgetary constraints may force us into a 5-well system for this site, requiring that two wells be located at one of the 3 sites to form the cluster in that fashion. For Western Hillsboro, where the site is defined, only the cluster question need be answered, and it is proposed with a 3-well system, one of which has already been constructed via an existing SFWMD research contract.