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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Groundwater and Groundwater Quality Policy 3. The use and disposal of toxic chemicals,the extraction of resources,and the disposal of wastes into injection wells shall be carefully controlled and monitored to protect water quality. San Joaquin County Mining Ordinance San Joaquin County has a quarry excavation standard [9-1415.3(u)]that requires a geohydrological analysis of the excavation-related impacts on groundwater resources for all quarry excavations that extend to depths below the groundwater level of the uppermost aquifer. The proposed Project must comply with this ordinance. Impact Analysis Approach and Methodology Impacts on groundwater and groundwater quality were assessed based on the results of technical reports prepared for the Project, estimates of water use during premising,mining, and post-mining operations that were provided by the Operator. Technical groundwater/hydrogeological studies were not prepared by the Operator. Construction and operation activities could result in direct and indirect impacts on groundwater and groundwater quality caused by ground disturbance or vegetation clearing as part of project construction and/or as a result of project operations. For analysis of impacts,three project stages are discussed: (1)premining, (2)active mining,and(3)post-mining reclamation. The premining stage is used to establish baseline conditions against which the following two stages may be compared. Active mining has the potential to affect >s+ local groundwater conditions through interception and pumping of groundwater below the water table during excavation activities and through spills of petroleum products or other chemicals from on-site vehicles and equipment. For the postmining reclamation stage,the presence of an open water storage site and reclamation as agricultural land could lead to groundwater contamination from use or spillage of agricultural chemicals. This analysis assumes that the applicant will comply with the County's Mining Ordinance [9-1415.3(u)] and will evaluate the potential impacts on groundwater resources as a result of the proposed Project. It was also assumed that the evaluation would include,but not be limited to,the following: ■ a detailed description of the existing groundwater resources, including but not limited to, local groundwater levels, the potential groundwater yield,the status of the groundwater basin(e.g.,overdraft), local groundwater quality, and the location of local wells; _:2�_" ■ a detailed quantification of the volume and rate of groundwater seepage that would occur into the pits during all stages of the mining operations; _ ■ a technical analysis and description of the potential groundwater level impacts at local wells, including a description of the minimum groundwater DeSilva Gates Quarry Project Draft Environmental Impact Report 3.H-5 J85 0.5105.05 ti