Review of the Everglades Aquifer Storage and Recovery Regional Study (2015) / Chapter Skim
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2 Topic-Specific Reviews
2 Topic-Specific Reviews
Pages 11-40
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From page 11... ...
Horizontal anisotropy of hydraulic conductivity can impact predictions of hydraulic head change and migration of stored water. Prior to the ASR Regional Study, the hydrostratigraphic description of the Floridan aquifer system suffered from inconsistencies and data gaps and potentiometric 2 Recovery efficiency is defined as "the percentage of the water volume stored that is subsequently recovered while meeting a target water quality criterion in the recovered water" (Pyne, 2005)
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From page 12... ...
The final hydrogeologic framework (Reese and Cunningham, 2014; summarized in Figure 2-1) indicates the presence of four major permeable zones within the Floridan aquifer system: the Upper Floridan aquifer, the Avon Park permeable zone (APPZ)
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From page 13... ...
and Reese and Alvarez-Zarikian (2007) reviewed aquifer test data from South Florida and found evidence for leaky behavior in the Upper Floridan aquifer attributed to leakage between permeable zones within the Upper Floridan aquifer or across the middle semiconfining unit 1; the overlying ICU is generally accepted to effectively prevent leakage (Reese, 2002)
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From page 14... ...
Mapping of surface lineaments was conducted as part of the regional-scale investigations. The Regional ASR TDR notes that surface lineaments may be related to fractures or faults that extend from the basement rocks to the land surface.
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From page 15... ...
Uncertainties Remaining Although uncertainties remain concerning the vertical distribution of hydraulic conductivity within permeable zones, horizontal anisotropy, and the effectiveness of confining layers, none of these preclude ASR. With the regional hydrogeologic framework established, future efforts at the local scale are needed to understand the variability in hydraulic connectivity within the Upper Floridan aquifer and the APPZ.
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From page 16... ...
A USGS study conducted outside of the ASR Regional Study (Reese and Alvarez-Zarikian, 2007) provides a useful synthesis of factors influencing ASR cycle test recovery efficiency based on 30 ASR wells completed in the Floridan aquifer system
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From page 17... ...
Determining the appropriate initial volume of the buffer zone requires information from ASR operations and testing (sometimes obtained from existing wells when an ASR wellfield is being expanded) , although existing ASR experiences in the Upper Floridan aquifer may be useful to inform the sizing of the target storage volume.
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From page 18... ...
Intervals of the APPZ with high transmissivity and salinity would be expected to have lower recovery efficiencies compared to the Upper Floridan aquifer.3 Additional work is needed to determine the recoveries feasible in the Upper Floridan aquifer or the APPZ at potential CERP ASR locations using a target storage volume approach, considering different storage periods. Continued study is also needed to determine the optimal well configuration for ASR to promote maximum recovery efficiency.
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From page 19... ...
are located near an existing or proposed surface storage reservoir. Both ASR pilot wells are sited near large surface storage reservoirs -- the Kissimmee River ASR is approximately 8,000 feet from Lake Okeechobee and the Hillsboro ASR is located adjacent to the Site 1 impoundment, which is under construction.
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From page 20... ...
analyses of the mechanical and elastic properties of core samples of Upper Floridan aquifer rock. The ASR Regional Study TDR reported that moderately low wellhead pressures (> 95 psi with no added safety factor)
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From page 21... ...
Could ASR pumping affect water quality at a regional scale? Could groundwater extraction during the recovery stage lower the artesian pressures within the Upper Floridan aquifer, making withdrawals more difficult for existing users of the Upper Floridan aquifer?
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From page 22... ...
Results of the model simulations suggest that the Upper Floridan aquifer would be unable to sustain the pumping requirements of 333 5 MGD ASR wells. Model analysis suggests that pump pressure and Artesian Pressures Protection Area requirements can be maintained with a 131-well configuration: 94 ASR wells in the Upper Floridan aquifer and 37 ASR wells in the Avon Park Permeable Zone (Scenario 11)
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From page 23... ...
Rather than continuing to refine the Regional Model, it may be more advantageous to shift the focus to application of local-scale flow and transport models to particular areas where ASR is planned, because local-scale models are more amenable to characterizing and simulating the heterogeneous and possibly anisotropic nature of the Floridan aquifer system. Based on the observations of preferential flow zones and bedding-plane dissolution in the Floridan aquifer system of South Florida, the possibility of turbulent flow conditions during ASR should be evaluated during cycle testing.
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From page 24... ...
Subsurface mixing with native water can also impact recovered water quality. Thus, the ASR Regional Study examined the water quality changes and related geochemical processes associated with ASR.
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From page 25... ...
Instead, the Regional Study team used existing water quality data from the SFWMD DBHYDRO database from 2000 to 2014 and conducted some limited additional sampling for trace metals and anthropogenic organic compounds over 1 year at the Kissimmee River ASR site. The array of constituents monitored was extensive but the number of samples and the frequency and duration of sampling and analysis were inconsistent across the sites for both surface water and groundwater.
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From page 26... ...
Field testing of subsurface microbial attenuation surrounding ASR wells was precluded by regulatory constraints. Uncertainties Remaining The studies described in the ASR Regional Study TDR and supporting documents identify the inorganic contaminants in source water that may be of concern to ASR operations.
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From page 27... ...
Arsenic ASR has the potential to mobilize arsenic in the subsurface when oxygen-rich surface waters oxidize pyrite, a common mineral in limestone in the Floridan aquifer system, and liberate arsenic bound within the pyrite structure (Arthur and Cowart, 2001; Mirecki et al., 2013)
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From page 28... ...
Uncertainties Remaining Some uncertainties remain regarding arsenic mobilization in future ASR implementation, considering differences in surface water chemistry across the region. For example, surface water at the Hillsboro site has much lower iron levels than the Kissimmee River and Port Mayaca sites.
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From page 29... ...
Another major uncertainty regarding the potential for ASR to enhance mercury methylation in the Everglades ecosystem involves increased sulfate loading to surface waters from ASR recovery water. The TDR presents sulfate concentration data from Upper Floridan aquifer and APPZ well samples taken across the region.
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From page 30... ...
Although sulfate concentrations throughout the Kissimmee River and Hillsboro ASR cycle tests were not reported, other cycle test data from ASR wells completed in the Upper Floridan aquifer (USACE and SFWMD, 2014, Appendix C) showed minimal changes in sulfate concentrations during storage but increasing sulfate in the recovery phase, as an increasing proportion of native groundwater was withdrawn during recovery.
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From page 31... ...
. The Regional Study provided some preliminary modeling to explore how increased sulfate could affect mercury methylation in Lake Okeechobee and the Everglades, but uncertainties remain.
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From page 32... ...
Today, water quality remains a major constraint for moving new water into the remnant Everglades, because without additional treatment systems the added water could lead to a violation of the Consent Decree. Phosphorus in ASR recovered water was not initially a major uncertainty for ASR, although the ASR Issue Team (1999)
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From page 33... ...
If substantial long-term phosphorus removal is documented, the feasibility of siting ASR wells south of Lake Okeechobee might be considered to provide both storage and phosphorus treatment to the remnant Everglades. Phosphorus removal via ASR north of Lake Okeechobee could help expedite the timeframe for reaching water quality targets in the lake, but it would not impact phosphorus loads to the Everglades in at least the next few decades, given the large reservoir of legacy phosphorus in the lake.
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From page 34... ...
However, these possible benefits need to be compared to potential environmental risks related to the water quality of the recovered water and its ecological effects when discharged into the environment. Possible hazards of ASR in South Florida include mobilization of arsenic from pyrite in the storage zones, release of sulfur in recovered waters that could promote methylation of mercury in receiving surface waters, and toxicity of recovered waters to aquatic plants and animals.
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From page 35... ...
. Water quality data inputs were based on an assessment of groundwater quality in the Upper Floridan aquifer at the Kissimmee River site, SFWMD surface water quality data, and Kissimmee River ASR recovered water quality.
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From page 36... ...
Uncertainties Remaining The recovery of stored water can result in substantial changes to surface water chemistry, and significant uncertainty remains about the magnitude of those changes under probable ASR scenarios and the resulting effects to aquatic life at local and regional scales. Thus, an improved understanding of the quality of recovered water is needed, with longer storage times and larger storage volumes and considering a target storage volume approach (assuming such an approach is feasible under regulatory constraints for arsenic)
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From page 37... ...
Additional bench-scale chronic toxicity tests should be performed under a variety of conditions using recovered water from multiple ASR sites, considering longer storage times, greater storage volumes, and buffer zone formation, which could improve water quality and decrease toxic effects. Additional attention should be given to examining changes in water hardness in recovered waters and how that affects the toxicity to sensitive aquatic invertebrates.
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From page 38... ...
In the end, the risk assessment should provide clear guidance based on these probabilities about the risks of different ASR scenarios and a quantitative evaluation of the inherent uncertainties associated with these conclusions. COSTS AND BENEFITS OF WATER STORAGE ALTERNATIVES One uncertainty that was not identified by either the ASR Issue Team (1999)
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From page 39... ...
This critical piece of information was, in turn, used in another facet of the study to better inform simulations of the effects of ASR operations on the water quality of Lake Okeechobee.
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From page 40... ...
Inactivation rates are necessary, but insufficient, for approximating the distances in which live, pathogenic microbes could penetrate into the aquifer during the recharge and storage phases of ASR. The analysis could have been strengthened by integrating data on inactivation rates with groundwater flow rates to estimate the areal extent of groundwater degradation resulting from introduction of pathogen containing waters during ASR operations.
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