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1

Introduction

Artificial recharge, i.e., the process by which water is directed into the ground to replenish an aquifer (NRC, 1994), has taken on increasing importance in recent decades. Aquifer storage and recovery (ASR), which is the major theme of this report, may be viewed as a sub-field within this more general area. In this report, ASR refers to, “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). This is shown conceptually in Figure 1. The advantages of this approach over other methods of artificial recharge may include reduced problems with plugging, economic benefits from the efficient use of the wells, and the potential to use aquifers with less than optimal water-quality characteristics (Pyne, 1995).

Importance of ASR to Comprehensive Everglades Restoration Plan (CERP)

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 ASR proposal 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). Based on the 1965-1995 record, average and maximum yearly recharge volumes in the Lake Okeechobee area are estimated to be about 264,000 acre-ft (86 billion gallons; 326 million m3) and 1,100,000 acre-ft (358 billion gallons; 1.36 billion m3) per year, respectively (USACE, 1999). The latter would require pumping all 200 proposed ASR wells in that region at capacity year round. Average yearly recovery volumes are estimated to be somewhat lower - about 136,000 acre-ft (44 billion gallons; 168 million m3) per year (USACE, 1999). ASR represents about one-fifth of the total cost of the CERP (Kwiatkowski, 2000a).

The CERP suggests that ASR may provide greater storage efficiency when compared to land requirements and high seepage and evapotranspiration rates associated with above ground reservoir storage (USACE, 1999). ASR may offer particular advantages over surface storage 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. ASR may also limit certain kinds of degradation (e.g., algal blooms, nutrient and pathogen inputs from birds, etc.) that may occur with surface storage. Potential disadvantages include losses to the aquifer due to mixing within saline aquifers, and low recharge and recovery rates relative to surface storage (USACE, 1999, Appendix B).

The ASR concept in South Florida involves the recharge of excess fresh surface and shallow groundwater during wet periods into the UFA through approximately 333 wells. This assumes recharge rates of about five million gpd (19,000 m3/day) per well; the exact number of wells would be a function of their long-term capacity. Ambient groundwater in the UFA is brackish to saline



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Page 6 1 Introduction Artificial recharge, i.e., the process by which water is directed into the ground to replenish an aquifer (NRC, 1994), has taken on increasing importance in recent decades. Aquifer storage and recovery (ASR), which is the major theme of this report, may be viewed as a sub-field within this more general area. In this report, ASR refers to, “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). This is shown conceptually in Figure 1. The advantages of this approach over other methods of artificial recharge may include reduced problems with plugging, economic benefits from the efficient use of the wells, and the potential to use aquifers with less than optimal water-quality characteristics (Pyne, 1995). Importance of ASR to Comprehensive Everglades Restoration Plan (CERP) 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 ASR proposal 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). Based on the 1965-1995 record, average and maximum yearly recharge volumes in the Lake Okeechobee area are estimated to be about 264,000 acre-ft (86 billion gallons; 326 million m3) and 1,100,000 acre-ft (358 billion gallons; 1.36 billion m3) per year, respectively (USACE, 1999). The latter would require pumping all 200 proposed ASR wells in that region at capacity year round. Average yearly recovery volumes are estimated to be somewhat lower - about 136,000 acre-ft (44 billion gallons; 168 million m3) per year (USACE, 1999). ASR represents about one-fifth of the total cost of the CERP (Kwiatkowski, 2000a). The CERP suggests that ASR may provide greater storage efficiency when compared to land requirements and high seepage and evapotranspiration rates associated with above ground reservoir storage (USACE, 1999). ASR may offer particular advantages over surface storage 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. ASR may also limit certain kinds of degradation (e.g., algal blooms, nutrient and pathogen inputs from birds, etc.) that may occur with surface storage. Potential disadvantages include losses to the aquifer due to mixing within saline aquifers, and low recharge and recovery rates relative to surface storage (USACE, 1999, Appendix B). The ASR concept in South Florida involves the recharge of excess fresh surface and shallow groundwater during wet periods into the UFA through approximately 333 wells. This assumes recharge rates of about five million gpd (19,000 m3/day) per well; the exact number of wells would be a function of their long-term capacity. Ambient groundwater in the UFA is brackish to saline

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Page 7 (CH2M Hill, 1989). Because of this high salinity, the UFA is currently used little in these areas for water supply. During the recharge phase of ASR system operation, the 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 ASR well. This bubble of fresh water could be drawn upon later by the same ASR wells and the recovered water used to augment deficient surface water supplies during dry seasons or longer-term drought periods. In essence, ASR would use subsurface space in the UFA as the reservoir for storing water. ~ enlarge ~ FIGURE 1. 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. Modified from http://www.sfwmd.gov/org/pld/proj/asr/asrdefine.htm . Concerns expressed about large-scale ASR in South Florida 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 m3/day). However, the proposed scale in the CERP of 1.7 billion gpd (6.3 million m3/day) is much larger than past projects. Implementation of ASR at the scale proposed in the CERP has raised a number of concerns among groundwater engineers and scientists 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 General Accounting Office (2000), were summarized in the following seven questions: 1. Are the proposed ASR source waters of suitable quality for recharge without extensive pretreatment?

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Page 8 2. What regional hydrogeologic information on the UFA is needed but unavailable for regional assessment? 3. Will the proposed ASR recharge volumes result in head increases sufficient to cause rock fracturing? 4. 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? 5. 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? 6. What, if any, is the potential impact of recovered water on mercury bioaccumulation in the surface environment? 7. What are the relationships among ASR storage zone properties, recovery rates, and recharge volumes? These questions and others were viewed by the Committee on Restoration of the Greater Everglades Ecosystem (CROGEE) as falling into three major categories, which were ultimately reflected in the organization of the workshop and this report: regional science issues, water quality issues, and local performance/feasibility issues. These are reflected as chapters two, three, and four of this report. The Lake Okeechobee and Western Hillsboro ASR Projects This section contains a brief description of the overall plans for ASR in these two regions ( Figure 2 ), including the pilot projects. It is taken almost entirely from USACE (1999). The project description, project background, and work breakdown structure from the Project Management Plans for the pilot projects are reproduced in Appendices E and F. The most recent drafts of the Project Management Plans, which are slightly revised from the drafts that the CROGEE evaluated, may be accessed at http://www.evergladesplan.org/projects/pilot/lake_o/lake_o_pp_main.htm and http://www.evergladesplan.org/projects/pilot/hillsboro/hillsboro_pp.htm , respectively. Lake Okeechobee. This feature of the CERP includes ASR wells with a combined capacity of one billion gpd (3.8 million m3/day) near Lake Okeechobee. These wells will be used in conjunction with a modified regulation schedule for the lake to achieve multiple-use purposes including storage capacity, flood control, and environmentally acceptable seasonal lake level fluctuations. About 200 wells with an assumed capacity of five million gpd (19,000 m3/day) each are anticipated in the CERP. Some level of pre- and post-treatment of water recharged and recovered during ASR operation is also anticipated. Testing of treatment technologies, after characterization of source water, is one component of proposed pilot tests. Lake Okeechobee water will be injected into the UFA when lake levels are forecast to rise to undesirable levels. During dry periods, when lake levels are forecast to fall to undesirable levels, water would be recovered from wells and returned to the lake. It is assumed (based on existing ASR facilities) that recovery of aquifer-stored water will have no adverse effects on water quality in Lake Okeechobee, and may, in fact, improve it with respect to nutrient load. The pilot project will investigate changes to water chemistry resulting from aquifer storage and identify any necessary post-recovery treatment requirements to improve water quality. The wells are designed to (1) provide additional regional storage with reduced evaporative losses and minimal land purchases compared to surface storage; (2) increase Lake Okeechobee's water storage capability to better meet regional water demands; (3) manage part of the regulatory releases from the lake primarily to improve Everglades hydropatterns and to meet supplemental

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Page 9 regional water-supply demands of the Lower East Coast; (4) reduce harmful discharges to the St. Lucie and Caloosahatchee Estuaries; and (5) maintain and enhance current levels of flood protection. ~ enlarge ~ FIGURE 2. Map of the locations of the Lake Okeechobee, Western Hillsboro, and other planned ASR sites. Wells shown are for schematic purposes only; the actual total number of planned wells is about 333. From SFWMD (2000). The pilot project is designed to provide benefit to environmental, urban and agricultural users. Its strategy is to install several exploratory/test ASR systems in geographically dispersed areas around the lake and to assess the feasibility of implementing ASR technology at a regional scale. Additionally, it will determine the water quality characteristics of waters to be injected, water recovered from the aquifer, and the water in the receiving aquifer. Information from the pilot project will provide the hydrogeological and geotechnical characteristics of the UFA at the pilot sites as well as a demonstration of the ability of the aquifer system to maintain injected water for future recovery. Western Hillsboro. A series of ASR wells with associated pre- and post- water quality treatment will be located next to an aboveground reservoir with a storage capacity of about 15,000 acre-feet (4.89 billion gallons; 18.5 million m3), or along the Hillsboro Canal. The combined ASR capacity would be about 150 million gpd (570,000 m3/day). The initial design of the facility assumed 30 well clusters at 5 million gpd (19,000 m3/day) per well. Some level of pre- and post-treatment of water recharged and recovered during ASR operation was anticipated in the CERP. Testing of treatment technologies, after characterization of source water, is one component of proposed pilot tests. Surface water and/or groundwater from the surficial aquifer adjacent to the

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Page 10 reservoir would be the source of recharge water. The location, extent of treatment and number of ASR wells may be modified based on the results of the pilot project. The purpose of this feature is to supplement water deliveries to the Hillsboro Canal during dry periods thereby reducing demands on Lake Okeechobee and the Loxahatchee National Wildlife Refuge. Surface water, possibly from the Hillsboro Canal, and shallow groundwater from along the margins of and below the reservoir, would be recharged when excess water is available, and would be released back 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. Other ASR projects. The CERP also proposes four other sites for ASR ( Figure 2). These include the C-43 Basin Storage Reservoir and Aquifer Storage and Recovery project in the Caloosahatchee River Region (44 wells), and three sites in Palm Beach County (total of 59 wells). All of these except the C-51 canal site ( Figure 2) are associated with above-ground or in-ground reservoirs. The Committee's Charge The CROGEE's statement of task defines its role as “...provid[ing] scientific guidance to multiple agencies charged with restoration and preservation of... the greater Everglades.... In addition to strategic assessments and guidance, the NRC will provide more focused advice on technical topics of importance to the restoration efforts when appropriate.” The CROGEE task of understanding and analyzing the ASR pilot projects was agreed upon as a high priority by both the Task Force and the NRC. Before the first drafts of the Project Management Plans were written, the project design team had already received input from the ASR Issue Team, and had conducted other workshops around Florida. Between the first and second drafts, they received further input from various governmental agency staff. In the week before the workshop, the CROGEE received word that the USACE and SFWMD were proposing to request funds to conduct a regional study in parallel with the pilot project ( Appendix C, topic 1). This was in response to feedback that the USACE and SFWMD had received from various individuals and institutions concerning the importance of understanding the regional hydrostratigraphic framework, aquifer properties, and hydrodynamics to evaluating the likely success of large-scale ASR. The Project Management Plans have evolved further since the CROGEE held its workshop. According to Kwiatkowski (2000b), the major addition to the Lake Okeechobee ASR PMP in version 3 is the inclusion of three test/monitoring wells at the sites proposed for the exploratory/ASR wells. Major deletions from both PMPs in version three are tasks such as regional groundwater and geochemical modeling, additional monitoring wells and hydrogeologic investigations, regional source-water quality characterization study, and regional fracture analysis. Many of these tasks will be considered for inclusion in the proposed ASR Regional Study. It should be noted that as of this writing the proposed ASR Regional Study does not yet have a formal commitment of funding, nor has a budget been proposed. Because of the fluid nature of what will or will not be included in the pilot projects (sensu stricto) and the regional ASR study, we consider this report to be a critique of the pilot projects and related plans. Unless otherwise specified, the term “feasibility studies” is used in this report to refer

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Page 11 to the overall set of plans to answer key questions about local, regional and water quality issues with respect to the potential for success of ASR. It should be noted that this report is not designed to 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. Finally, the entire CERP is based on the principle of adaptive assessment. Thus, the committee viewed this set of plans from the perspective of the extent to which they will contribute to process understanding that can improve design and implementation of restoration project components. In the next three chapters, we evaluate the feasibility studies from the perspective of whether they will address the major questions in the areas of regional science, water quality, and local performance/feasibility.