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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Groundwater and Groundwater Quality conditions. The County and the Central Valley RWQCB will be the lead agencies involved in matters of groundwater quality degradation. Mitigation Measure GW-1b: Maintain Well Offsets The project proponent will maintain minimum San Joaquin County Health Department offsets between the mine and adjoining property lines to ensure that all nearby water supply wells are appropriately distant from potential sources of contamination. Health department offsets are considered sufficient to shield down-gradient wells from any microbiological contamination. Impact GW-2: Reclamation-Related Impacts on Groundwater Quality (Less than Significant with Mitigation) Dry Pit Reclaimed gravel mines could represent a hazard to groundwater quality by providing a more direct pathway for contaminants to contact groundwater and — circumvent normal recharge paths, such as soil percolation. The reclamation pit could adversely affect groundwater quality if it became contaminated by outside sources of pollution or spills, including illicit dumping. The potential for contamination represents a potentially significant impact on local water quality. In addition,the potential use of the North Pit Stage III as an agricultural storage pond would create an open body of water with direct connectivity to the aquifer. As such, it would have increased exposure to potential contaminants(including those from agricultural operations such as pesticides and fertilizers)and provide a vector for contamination of the aquifer. This would be considered a potentially significant impact. Mitigation Measures GW-la and GW-lb, described above,would reduce this impact to a less-than-significant level. Wet Pit The potential groundwater quality impacts as part of the wet pit operations would be greater than those described under the dry pit discussion. The pits during the wet pit operations would not be dewatered and would therefore provide more open water bodies with direct connectivity to the aquifer than the dry pit operations. These open water bodies would have increased exposure to potential contaminants(including those from agricultural operations such as pesticides and fertilizers) and provide a vector for contamination of the aquifer. The potential for contamination represents a potentially significant impact on local water quality. In addition, the potential use of the North Pit Stage III as an agricultural — storage pond would create another body of water, following the completion of mining operations,with direct connectivity to the aquifer. Mitigation Measures GW-la and GW-Ib, described above,would reduce this impact to a less- _ than-significant level. DeSilva Gates Quarry Project — Draft Environmental Impact Report 3.H-8 ,185 05105,05