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5

Summary and Conclusions

The Committee on Restoration of the Greater Everglades Ecosystem (CROGEE) has identified three general areas in which additional data and studies are required to address uncertainties related to feasibility and optimal design of regional ASR systems intended to provide storage required by the CERP. First, an improved understanding of the regional hydrogeologic framework, at the level of detail required to construct a regional scale numerical model of groundwater flow, is essential to assessing regional scale feasibility and impacts of the proposed regional ASR systems. Second, an improved understanding of water quality changes that will occur during storage of freshwater in the subsurface, and of the effects of modified water quality on human and ecological recipients of this water, is required to determine the chemical characteristics that can be used in assessments of recovery efficiency or recoverability at individual ASR wells. Third, an improved understanding of how local hydrogeologic properties (e.g., vertical distribution of hydraulic conductivity) and well construction features (e.g., location and length of open interval for recharge and recovery) interact to enhance or limit well capacity and recovery efficiency is required for optimal design of individual wells and well clusters.

Better understanding in these three areas of uncertainty will require studies that extend beyond the scope of the ASR pilot projects, at least as they have been described in draft project management plans. In these plans, it appears that the pilot studies are almost exclusively devoted to local feasibility issues. A regional study and modeling effort has been proposed recently as a separate project, but it has not been authorized or funded. While the pilot projects will generate some of the data needed to anticipate water quality changes during storage, studies to assess the appropriate water quality standards for discharge of recovered water to ecosystems are not part of any current or planned projects of the CERP. The pilot projects could, in principle, provide data needed to elucidate relationships between hydrogeologic properties and well construction characteristics. However, the pilot studies will be successful in providing such data only if they are carefully designed to test and monitor a variety of storage intervals under a range of well construction and operational conditions.

Many of the recommendations in the preceding chapters have been made previously by other groups, in particular the ASR Issue Team. Foremost among these is the need for a regional hydrogeologic synthesis and model to allow assessment of regional-scale feasibility and impacts of the proposed regional ASRs. Ideally the regional synthesis and modeling would precede any local scale feasibility studies such as those planned as part of the authorized pilot studies. This would allow the site selection for pilot studies to make use of regional information and also could provide a mechanism for using the pilot study sites to fill critical data gaps in the regional hydrogeologic framework. Given that the planning for the pilot studies already is well underway, it is even more important that a regional study be funded and initiated in the near future to optimize coordination of data collection at local and regional scales.

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 with other storage options in terms of overall performance, including storage capacity and cost effectiveness. This will



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Page 21 5 Summary and Conclusions The Committee on Restoration of the Greater Everglades Ecosystem (CROGEE) has identified three general areas in which additional data and studies are required to address uncertainties related to feasibility and optimal design of regional ASR systems intended to provide storage required by the CERP. First, an improved understanding of the regional hydrogeologic framework, at the level of detail required to construct a regional scale numerical model of groundwater flow, is essential to assessing regional scale feasibility and impacts of the proposed regional ASR systems. Second, an improved understanding of water quality changes that will occur during storage of freshwater in the subsurface, and of the effects of modified water quality on human and ecological recipients of this water, is required to determine the chemical characteristics that can be used in assessments of recovery efficiency or recoverability at individual ASR wells. Third, an improved understanding of how local hydrogeologic properties (e.g., vertical distribution of hydraulic conductivity) and well construction features (e.g., location and length of open interval for recharge and recovery) interact to enhance or limit well capacity and recovery efficiency is required for optimal design of individual wells and well clusters. Better understanding in these three areas of uncertainty will require studies that extend beyond the scope of the ASR pilot projects, at least as they have been described in draft project management plans. In these plans, it appears that the pilot studies are almost exclusively devoted to local feasibility issues. A regional study and modeling effort has been proposed recently as a separate project, but it has not been authorized or funded. While the pilot projects will generate some of the data needed to anticipate water quality changes during storage, studies to assess the appropriate water quality standards for discharge of recovered water to ecosystems are not part of any current or planned projects of the CERP. The pilot projects could, in principle, provide data needed to elucidate relationships between hydrogeologic properties and well construction characteristics. However, the pilot studies will be successful in providing such data only if they are carefully designed to test and monitor a variety of storage intervals under a range of well construction and operational conditions. Many of the recommendations in the preceding chapters have been made previously by other groups, in particular the ASR Issue Team. Foremost among these is the need for a regional hydrogeologic synthesis and model to allow assessment of regional-scale feasibility and impacts of the proposed regional ASRs. Ideally the regional synthesis and modeling would precede any local scale feasibility studies such as those planned as part of the authorized pilot studies. This would allow the site selection for pilot studies to make use of regional information and also could provide a mechanism for using the pilot study sites to fill critical data gaps in the regional hydrogeologic framework. Given that the planning for the pilot studies already is well underway, it is even more important that a regional study be funded and initiated in the near future to optimize coordination of data collection at local and regional scales. 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 with other storage options in terms of overall performance, including storage capacity and cost effectiveness. This will

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Page 22 require examination of related issues that were not addressed in any detail during the workshop, but are important to the overall assessment of ASR feasibility and effectiveness. Some of the topics that should be addressed in the design and evaluation of ASR systems are listed below. Once information from this work is available, it may be important to refine the analysis of overall performance of surface and subsurface storage, particularly if anticipated recovery efficiency for ASR differs significantly from the value of 70% assumed in model runs used to develop the CERP. Estimated evaporation losses from surface reservoirs should be compared with anticipated subsurface losses to the aquifer during ASR in order to quantify relative performance of surface and subsurface storage options. A significant increase or decrease in recovery efficiency would dictate re-examination of the number of wells required for a regional ASR system. Similarly, if recharge capacities for efficient operation of ASR wells differ significantly from 5 million gpd (19,000 m3/day) assumed in the CERP, it may also be necessary to re-evaluate the number of wells required to provide the necessary storage capacity. Estimates of energy costs for long-term operation should include contingencies for possible changes in fuel costs 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.