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Introduction

This report reviews plans for a regional study related to a water storage and recovery component of the Comprehensive Everglades Restoration Plan (CERP). The CERP is a framework and guide to restore, protect, and preserve the water resources of central and southern Florida, including the Everglades. It covers an 18,000-square-mile area, includes more than 60 elements, and will take more than 30 years to implement. It is designed to capture, store and redistribute fresh water previously lost to tide and to regulate the quality, quantity, timing and distribution of water flows. Among its many features are removal of barriers to sheetflow, wastewater reuse, treatment wetlands, surface water storage reservoirs, and underground water storage (USACE, 1999).

OPTIONS FOR WATER STORAGE IN THE CERP

The need for water storage for the CERP has led to the proposal to drill over 300 aquifer storage and recovery (ASR) wells in South Florida (Figure 1). ASR is “the storage of water in a suitable aquifer through a well during times when water is available, and recovery of the water from the same well during times when it is needed” (Pyne, 1995). A conceptual diagram of an ASR well in south Florida is shown in Figure 2. The CERP would use porous and permeable units in the Upper Floridan aquifer (UFA) to store excess surface water and shallow groundwater at rates of up to 1.7 billion gallons per day (gpd) (6.3 million m3/day) during wet periods for recovery during seasonal or longer-term dry periods (USACE, 1999; SFWMD, 2000). Ambient groundwater in the UFA is brackish to saline. During the recharge phase of ASR system operation, ambient groundwater would be displaced by the injected fresh water such that a zone, or “bubble,” of fresh water would be created and stored around each well. This bubble of fresh water could be drawn upon later by the same ASR wells during dry seasons or droughts. In practice, the bubble may be highly irregular, especially in karstic and fractured aquifers such as the UFA.2



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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration 1 Introduction This report reviews plans for a regional study related to a water storage and recovery component of the Comprehensive Everglades Restoration Plan (CERP). The CERP is a framework and guide to restore, protect, and preserve the water resources of central and southern Florida, including the Everglades. It covers an 18,000-square-mile area, includes more than 60 elements, and will take more than 30 years to implement. It is designed to capture, store and redistribute fresh water previously lost to tide and to regulate the quality, quantity, timing and distribution of water flows. Among its many features are removal of barriers to sheetflow, wastewater reuse, treatment wetlands, surface water storage reservoirs, and underground water storage (USACE, 1999). OPTIONS FOR WATER STORAGE IN THE CERP The need for water storage for the CERP has led to the proposal to drill over 300 aquifer storage and recovery (ASR) wells in South Florida (Figure 1). ASR is “the storage of water in a suitable aquifer through a well during times when water is available, and recovery of the water from the same well during times when it is needed” (Pyne, 1995). A conceptual diagram of an ASR well in south Florida is shown in Figure 2. The CERP would use porous and permeable units in the Upper Floridan aquifer (UFA) to store excess surface water and shallow groundwater at rates of up to 1.7 billion gallons per day (gpd) (6.3 million m3/day) during wet periods for recovery during seasonal or longer-term dry periods (USACE, 1999; SFWMD, 2000). Ambient groundwater in the UFA is brackish to saline. During the recharge phase of ASR system operation, ambient groundwater would be displaced by the injected fresh water such that a zone, or “bubble,” of fresh water would be created and stored around each well. This bubble of fresh water could be drawn upon later by the same ASR wells during dry seasons or droughts. In practice, the bubble may be highly irregular, especially in karstic and fractured aquifers such as the UFA.2

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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration Figure 1. Proposed ASR Systems in the Compresensive Everglades Restoration Plan

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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration FIGURE 2. Schematic diagram of the recharge and recovery phases of ASR for a typical south Florida system. The relatively symmetric spread of fresh water away from the well shown assumes a fairly homogeneous, isotropic aquifer with negligible regional flow relative to the flow rates induced by pumping during recharge or recovery. The actual configuration of the storage bubble may be considerably more complex. SOURCE: NRC, 2001. ASR has advantages and disadvantages compared to surface storage. ASR systems generally take up less land and may avoid water losses due to seepage and evapotranspiration (USACE, 1999). This is of particular importance in south Florida, where land acquisition costs are high and flat topography coupled with a shallow water table place constraints on surface reservoir construction. Additional advantages cited for this strategy are that ASR wells can be located in areas of greatest need, thus reducing water distribution costs, and that ASR permits recovery of large volumes of water during severe, multi-year droughts to augment deficient surface water supplies. Potential disadvantages of ASR wells include low recharge and recovery rates relative to surface storage, which limit capture rates of excess water, and losses due to mixing within brackish or saline aquifers (USACE, 1999). While slightly brackish water may be acceptable for drinking water, increases in salinity, and other water quality changes resulting from inputs of ASR water to surface ecosystems, may have unknown ecological effects. Operations and maintenance costs may also be higher for ASR, largely due to high energy requirements. Because of the complementary strengths of ASR and surface storage, these two storage options may be used in tandem. PREVIOUS RECOMMENDATIONS CONCERNING ASR While ASR technology has been employed successfully in Florida since 1983 (Pyne, 1995), with individual well clusters having capacities up to about ten million gpd (38,000

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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration m3/day), concerns have been expressed about the use of large-scale ASR in south Florida. Many of these concerns were outlined in a report prepared by the Aquifer Storage and Recovery Issue Team of the South Florida Ecosystem Restoration Working Group (ASR Issue Team, 1999) and presented to the Working Group in January 1999. The concerns addressed by the Issue Team, some of which were also noted in U.S. General Accounting Office (2000), were summarized in the following seven questions: Are the proposed ASR source waters of suitable quality for recharge without extensive pretreatment? What regional hydrogeologic information on the UFA is needed but unavailable for regional assessment? Will the proposed ASR recharge volumes result in head increases sufficient to cause rock fracturing? What will be the combined regional head increases from the regional scale ASR, and how will this affect individual ASR operation, change patterns of groundwater movement, and impact existing ASR wells, supply wells, or underground injection control (UIC) monitoring wells? What are the likely water quality changes to the injected water resulting from movement and storage in the aquifer, and will the quality of the recovered water pose environmental or health concerns? What, if any, is the potential impact of recovered water on mercury bioaccumulation in the surface environment? What are the relationships among ASR storage zone properties, recovery rates, and recharge volumes? These reports were considered in the formulation of project management plans (PMPs) for CERP ASR pilot projects for the Lake Okeechobee, Western Hillsboro, and Caloosahatchee River regions (http://www.evergladesplan.org/pm/mgmtplns.shtml). The first two of these were evaluated by the CROGEE in a workshop in 2000. This resulted in a report (NRC, 2001) that recommended additional research on regional science and water quality issues. These included the following: Development of a preliminary list of data needs and compilation of available data for a regional assessment, Development of a regional-scale groundwater flow model in parallel with initial data compilation to identify data gaps, Drilling of exploratory wells in key areas, including core sampling, downhole geophysical logging, hydraulic testing and water quality sampling, 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 multi-objective approach to ASR facility siting during final design of the regional ASR systems, 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,

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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration 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, and Studies designed to enhance understanding of mechanisms responsible for mixing of dilute recharge water with brackish to saline groundwater (NRC, 2001). GOALS OF ASR REGIONAL STUDY The ASR Regional Study was conceived just prior to the abovementioned CROGEE workshop, and was designed to answer many of these questions. Its authors, the members of a broad, interagency “project delivery team,” stated that the study “will investigate regional technical and regulatory issues governing the feasibility of full-scale ASR implementation, as identified in the CERP, and develop tools to assess the feasibility and increase the level of certainty of successful ASR implementation” (CERP, 2002). According to the Executive Summary of the PMP (included as part of Appendix A in this report) the primary goals of the ASR Regional Study are the following: Address outstanding issues of a regional nature that cannot be adequately addressed by the authorized ASR Pilot Projects, Reduce uncertainties related to full-scale CERP ASR implementation by conducting scientific studies based on existing and newly acquired data and evaluate potential effects on water levels and water quality within the aquifer systems, and on existing users, surface-water bodies, and the flora and fauna that inhabit them, and Develop a regional groundwater model of the Floridan Aquifer System (FAS) and conduct predictive simulations to evaluate the technical feasibility of the proposed 333-well CERP ASR system, or if determined to be infeasible, identify an appropriate magnitude of ASR capacity with minimal impact to the environment and existing users of the FAS (CERP, 2002). REPORT OBJECTIVE AND OVERVIEW A fourth draft of the ASR Regional Study PMP was prepared by the USACE and the SFWMD in May 2002, and the Task Force requested that the CROGEE conduct a technical review of that document. The executive summary and table of contents for the PMP are shown in Appendix A. The entire PMP, including appendices, may be found online at http://www.evergladesplan.org/pm/mgmtplns.shtml. The PMP is organized primarily into a series of “technical tasks,” each having a budget, a timetable, subtasks, and a list of assumptions. Most of this report focuses on Chapter 3 of the PMP, which outlines the technical tasks. There is also considerable discussion of Appendix L, which contains many of the details of Tasks 10 through 13 (water quality and ecological studies). This review examines the adequacy of the proposed scientific methods to address key issues raised in the CROGEE February 2001 report and other issues previously raised by the ASR Issue Team of the South Florida Ecosystem Restoration Working Group. As with NRC (2001), the principle of adaptive management forms a backdrop to the report. That is, the plans

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Regional Issues in Aquifer Storage and Recovery for Everglades Restoration are evaluated from the perspective of how they will contribute to process understanding that can improve design and implementation of restoration project components. Following an overall assessment of the PMP, Chapter 2 of this report focuses on the “tasks” outlined in the “Project Scope” of the PMP, in the order in which they are introduced in that document. Chapter 3 addresses other technical issues that are not directly related to these tasks. Chapter 4 summarizes the conclusions and recommendations of this review.