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Executive Summary

Aquifer storage and recovery (ASR) is a process by which water is recharged through wells to an aquifer and extracted for beneficial use at some later time from the same wells. ASR is proposed as a major water storage component in the Comprehensive Everglades Restoration Plan (CERP), developed jointly by the U.S. Army Corps of Engineers (USACE) and the South Florida Water Management District (SFWMD). The plan would use the Upper Floridan aquifer (UFA) to store as much as 1.7 billion gallons per day (gpd) (6.3 million m3/day) of excess surface water and shallow groundwater during wet periods for recovery during seasonal or longer-term dry periods, using about 333 wells. ASR represents about one-fifth of the total estimated cost of the CERP.

ASR may have advantages over surface storage in south Florida in that it may limit losses due to evaporation when compared with surface storage and limit the acreage of land removed from other productive uses. It also may permit the recovery of large volumes of water during severe, multi-year droughts to augment deficient surface water supplies.

Concerns about the role of ASR in the CERP

Concerns have been voiced about the use of ASR. Some of these are related to its proposed scale, which is much larger than existing ASR projects in Florida. Regional issues include the relative scarcity of subsurface information in areas where ASR wells will be located, and impacts of the combined hydraulic head increases from the regional scale ASR on existing ASR wells, supply wells, and underground injection control (UIC) monitoring wells. Water quality issues include the suitability of the source waters for recharge without extensive pretreatment, likely water quality changes during storage in the aquifer, and whether the quality of the recovered water will pose environmental or health concerns. Local performance issues include whether the proposed ASR injection volumes will result in pressures sufficient to cause rock fracturing, and lack of information concerning the relationships among ASR storage zone properties, recovery rates, and recharge volumes.

The pilot projects

To address some of these issues, the CERP proposed several ASR pilot projects, two of which were approved in the 1999 Water Resources Development Act (WRDA) and are the subject of this report.

Lake Okeechobee. According to the draft project management plan (PMP), this pilot project is designed to test the feasibility of placing about 200 ASR wells with an estimated capacity of one billion gpd (3.8 million m3/day) near Lake Okeechobee. The full-scale CERP feature is designed to (1) provide regional storage, (2) increase the lake's water storage capability, (3) better manage regulatory releases from the lake; (4) reduce harmful discharges to the St. Lucie and Caloosahatchee estuaries; and (5) enhance flood protection.



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Page 1 Executive Summary Aquifer storage and recovery (ASR) is a process by which water is recharged through wells to an aquifer and extracted for beneficial use at some later time from the same wells. ASR is proposed as a major water storage component in the Comprehensive Everglades Restoration Plan (CERP), developed jointly by the U.S. Army Corps of Engineers (USACE) and the South Florida Water Management District (SFWMD). The plan would use the Upper Floridan aquifer (UFA) to store as much as 1.7 billion gallons per day (gpd) (6.3 million m3/day) of excess surface water and shallow groundwater during wet periods for recovery during seasonal or longer-term dry periods, using about 333 wells. ASR represents about one-fifth of the total estimated cost of the CERP. ASR may have advantages over surface storage in south Florida in that it may limit losses due to evaporation when compared with surface storage and limit the acreage of land removed from other productive uses. It also may permit the recovery of large volumes of water during severe, multi-year droughts to augment deficient surface water supplies. Concerns about the role of ASR in the CERP Concerns have been voiced about the use of ASR. Some of these are related to its proposed scale, which is much larger than existing ASR projects in Florida. Regional issues include the relative scarcity of subsurface information in areas where ASR wells will be located, and impacts of the combined hydraulic head increases from the regional scale ASR on existing ASR wells, supply wells, and underground injection control (UIC) monitoring wells. Water quality issues include the suitability of the source waters for recharge without extensive pretreatment, likely water quality changes during storage in the aquifer, and whether the quality of the recovered water will pose environmental or health concerns. Local performance issues include whether the proposed ASR injection volumes will result in pressures sufficient to cause rock fracturing, and lack of information concerning the relationships among ASR storage zone properties, recovery rates, and recharge volumes. The pilot projects To address some of these issues, the CERP proposed several ASR pilot projects, two of which were approved in the 1999 Water Resources Development Act (WRDA) and are the subject of this report. Lake Okeechobee. According to the draft project management plan (PMP), this pilot project is designed to test the feasibility of placing about 200 ASR wells with an estimated capacity of one billion gpd (3.8 million m3/day) near Lake Okeechobee. The full-scale CERP feature is designed to (1) provide regional storage, (2) increase the lake's water storage capability, (3) better manage regulatory releases from the lake; (4) reduce harmful discharges to the St. Lucie and Caloosahatchee estuaries; and (5) enhance flood protection.

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Page 2 The stated purposes of the pilot project are to (1) install several exploratory/test ASR systems in geographically dispersed areas around the lake, (2) determine the water quality characteristics of waters to be recharged, water recovered from the aquifer, and the water in the receiving aquifer, (3) provide an estimate of the amount of water that can be recharged, and (4) provide hydrogeological and geotechnical information on the UFA within the region, and the ability of the UFA to maintain injected water for future recovery. Western Hillsboro. This CERP feature involves a series of ASR wells that would be located next to an above-ground reservoir in Palm Beach County, or along the Hillsboro Canal. The ASR capacity would be about 150 million gpd (570,000 m3/day), from 30 wells pumping at 5 million gpd (19,000 m3/day) per well. Surface water and/or groundwater from the surficial aquifer adjacent to the reservoir would be the source of recharge water. This feature is designed to supplement water deliveries to the Hillsboro Canal during dry periods, thereby reducing demands on Lake Okeechobee and the Loxahatchee National Wildlife Refuge. Water would be pumped into the UFA during times of excess, and returned to the canal to help maintain canal stages during the times of deficit. The stated purposes of the pilot project are (1) to determine the most suitable sites and the optimum configuration for the ASR wells in the vicinity of the reservoir, (2) to evaluate many of the hydrogeological and geotechnical characteristics of the soils and aquifer in the area, and (3) to determine the specific water quality characteristics of water within the aquifer, water proposed for recharge, and water recovered from the aquifer. The Committee's Charge The National Research Council's Committee on Restoration of the Greater Everglades Ecosystem (CROGEE) examined the second draft of the pilot project PMPs from the perspective of adaptive assessment, i.e., the extent to which the pilot projects will contribute to process understanding that can improve design and implementation of restoration project components. It organized a workshop in Miami, Florida on October 19, 2000 to discuss these plans with SFWMD and USACE personnel and other interested parties. Immediately prior to the workshop, much of the proposed work on regional analysis of the subsurface was extracted from the pilot projects and reorganized into a planned, but as yet unfunded, regional ASR study. Because the CROGEE concludes that this regional work is crucial to evaluating the potential for success of the ASR elements of the CERP, this report is a critique of the pilot projects (sensu stricto) and related studies. This report does not make judgements regarding the overall desirability of ASR as a major component of the CERP, either in absolute terms or in comparison with other storage options such as surface reservoir storage. The committee's recommendations are organized into three categories—regional science issues, water quality issues, and local performance/feasibility issues—and are as follows:

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Page 3 Regional Science Issues The scale of the proposed ASR projects is unprecedented, with approximately 1.7 billion gpd (6.3 million m3/day) concentrated in a relatively small area compared with the current total withdrawal of about 3 billion gpd (11 million m3/day) that is pumped regionally from the UFA. It is critical to assess the aggregate hydraulic effects of ASR wells on the existing UFA flow system. This will require a regional hydrogeologic assessment and interpretation of the ASR pilot projects within a regional context. Recently developed plans to pursue funding for a regional study beyond the constraints of the pilot projects are commendable. Essential elements of the regional study should include the following. Development of a preliminary list of data needs and compilation of available data for a regional assessment. This task should be undertaken as soon as possible. Development of a regional-scale groundwater flow model. Model development should proceed in parallel with initial data compilation, and can be used to identify data gaps. Drilling of exploratory wells in key areas, including core sampling, downhole geophysical logging, hydraulic testing and water quality sampling of these wells. Seismic reflection surveys, used in conjunction with results from exploratory wells, to constrain the three-dimensional geometry and continuity of hydrostratigraphic units. Use of the regional model in conjunction with other regional data sets to develop a rational, multi-objective approach to ASR facility siting during final design of the regional ASR systems. Water Quality Issues ASR water may be used for agriculture, for augmenting water inflows to natural ecosystems in the Everglades, and, indirectly, to supplement municipal (drinking water) supplies. Different regulations and different concerns about water quality arise in connection with these different intended uses. Thus, considerations must be broader than simply meeting existing water quality criteria. The chemical analyses planned as part of the pilot projects are insufficient to answer many questions about potential biological impacts of ASR water on the Everglades ecosystem. Such analyses, by themselves, also cannot provide the mechanistic information needed to develop geochemical models to predict how water chemistry/water quality will change in a full-scale ASR program. Water quality studies related to ASR should be expanded to include the following. Scientific studies, including laboratory and field bioassays and ecotoxicological studies, to help determine appropriate standards that consider not only the initial receptors of the recovered water, but also downstream receptors. Characterization of organic carbon of the source water and studies designed to anticipate the effects of this material on biogeochemical processes in the subsurface. These are a high priority because recharge water is likely to have high concentrations of dissolved organic carbon compared with ambient water in the aquifer. Laboratory studies to evaluate dissolution kinetics and redox processes that could release major ions, heavy metals, arsenic, radionuclides, and other constituents from the aquifer matrix. These should be undertaken before (and/or in parallel with) water quality monitoring during cycle testing.

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Page 4 Studies designed to enhance understanding of mechanisms responsible for mixing of dilute recharge water with brackish to saline groundwater. These are necessary to predict changes in dissolved solids due to mixing. Local Performance/Feasibility Issues In keeping with the principle of adaptive assessment, the CROGEE recommends that the pilot projects not be considered simply as demonstrations at particular sites. Instead, they should be viewed as an opportunity to develop a better understanding of the hydrogeologic and well construction characteristics that control the relationships between storage intervals, recharge volumes, and recoverability. Therefore, the pilot projects should be designed to maximize the value of the data obtained for improving understanding of ASR performance at both the specific sites tested and more generally in the UFA. In case of budget constraints, it would be preferable to do more detailed studies with enhanced monitoring at a reduced number of sites or with a reduced number of ASR wells, rather than more limited studies using the currently planned number of exploratory wells. Important elements that should be considered in design of the pilot tests are listed below. Monitoring wells that allow sampling at discrete depths and in a variety of directions from the recharge well. These should be a high priority at each pilot ASR site for purposes of delineating bubble geometry, potential preferential flow paths, and the extent of mixing between recharged and ambient water. Tests designed to compare effects of short and long sections of open borehole on well performance. These would be particularly useful for optimizing design of ASR wells. Continued recharge of the Lake Okeechobee pilot wells for periods on the order of a year or more during cycle testing. Hydrologic models indicate that continuous recharge is likely to be required for multi-year periods. Effects of mixing and water-rock interactions over these time periods may not be readily predicted on the basis of short-term cycle results. Use of observations obtained from a suitable network of monitoring wells, and over suitable time periods, to develop new or improved conceptual and numerical models of “bubble” migration. Such models may need to account for three-dimensional, density dependent flow and solute transport in multi-permeability media containing fractures and solution conduits. General Conclusions An improved understanding in these three areas of uncertainty – regional science, water quality, and local feasibility – will require studies that go beyond the scope of the proposed ASR pilot projects, which are almost exclusively devoted to local feasibility issues. A regional study and modeling effort recently was proposed as a separate project, but has not been authorized or funded. Ideally, this would precede any local-scale feasibility studies to allow these studies to make use of regional information. The pilot projects are also lacking studies to help assess the appropriate water quality standards for discharge of recovered water to ecosystems. Information from the regional study, water quality studies, and local scale pilot studies ultimately must be synthesized and used together in the overall assessment of ASR as a component of the CERP. With an improved understanding of ASR systems that will result from these studies, it should be possible to develop ASR system designs that then can be compared to other storage options in terms of overall performance, including storage capacity and cost effectiveness. This will require further examination of related issues that were not the focus of the workshop, but are

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Page 5 important to the overall assessment of ASR feasibility and effectiveness. These include performance of surface and subsurface storage, a comparison of losses from surface evaporation and subsurface storage, the number and distribution of wells required for a regional ASR system, and estimates of energy costs for operation over the anticipated project life. As a final comment, the CROGEE notes that the CERP calls for ASR to be implemented in phases. The Committee agrees that phased implementation is an appropriate strategy and strongly recommends a) thorough evaluation of the environmental effects of each incremental increase in scale of ASR, and b) ongoing adaptive assessment of the program.