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    4. Effects of dissolved and particulate organic matter in recharge water on biogeochemical processes in the subsurface environment and the potentially adverse effects of these processes on ASR system functioning.

    5. Rates of mineral dissolution reactions in the aquifer storage zone that could release heavy metals, arsenic, radionuclides, and major ions from the geological matrix into water that is to be recovered for use as drinking water or to supplement flows to the Everglades.

    6. Mechanisms of mixing of relatively dilute recharge water with more saline pore fluids in the storage zone, which will affect the extent to which water quality is changed during the aquifer storage and recovery process.

Conclusions and Recommendations

The CROGEE concludes that ASR water used in the Everglades restoration will probably need to achieve concentrations for some variables that are lower than existing Florida numerical water quality criteria for drinking water. Likewise, Florida's existing Class III water quality criteria (i.e., criteria for protection of fish and wildlife) may not be sufficient to ensure that use of ASR water does not have negative ecological impacts. This is partly due to the great diversity in chemical composition among surface waters within South Florida. For example, surface waters in the southern part of the Everglades have low concentrations of ions, whereas waters in Lake Okeechobee and waters just to the south of the lake have relatively high ionic content. The species composition of plant life growing in these waters reflects the chemical composition of the water. Specifically, native flora of the soft water in the southern Everglades are adapted to those conditions. If the use of recovered ASR water during periods of low rainfall increases the ionic strength of Everglades water (see Mirecki et al., 1998, for example), the composition of the plant community may change significantly even though the water may meet all existing criteria.

The likelihood of such changes cannot be determined merely by conducting chemical analyses as part of the pilot program nor even by short-term laboratory-scale bioassays. The CROGEE recommends that ecotoxicological studies, including long-term bioassays conducted at the field scale, be undertaken during the period of the pilot program to evaluate the ecological impacts of water quality changes resulting from broad use of ASR water to supplement inflows to the Everglades during droughts.

Water recharged to ASR wells will come primarily from Lake Okeechobee and other impoundments. The source waters and surrounding lands can and should be managed to minimize the occurrence of pathogens in the water being pumped down the wells. However, because these surface water bodies may contain viruses and bacteria that are not naturally present in the aquifer system, the CROGEE recognizes that pathogen die-off studies need to be performed as part of the permitting process. It recommends that those studies be done under conditions as realistic of the full-scale ASR process as possible. For example, aquifer materials and their resident microbial communities can be returned to the laboratory for experimentation. In instances in which it is impossible to obtain core segments, drill cuttings can be substituted, although this may result in a substantial loss in the quantitative value of the results. In particular, die-off studies should focus on the pathogenic species of concern, especially viruses, rather than on model microorganisms, whose survival rates may not necessarily mimic those of actual pathogenic species.

The source water for recharge will be relatively high in dissolved organic matter, and, depending on the degree of filtration, may contain some particulate carbon as well. The biodegradation of this material within the aquifer could have major impacts on aquifer chemistry in the



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