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San Joaquin County Community Environmental Setting, Impacts,and Mitigation Measures Development Department Groundwater and Groundwater Quality level necessary for local well owners to be unaffected by the project, and an analysis of the seepage rates,evaporation,and infiltration rates at the settling - ponds; _ Z ■ a technical analysis of the Project's consumptive use of groundwater; 1d P A y+�■ an evaluation of the cumulative impacts on groundwater resources; and 3 �' ■ a description of potential groundwater quality impacts. Thresholds of Significance Based on the State CEQA Guidelines,the proposed Project would result in a — significant impact on groundwater and groundwater quality if it would: ■ violate any water quality standards or waste discharge requirements, _ ■ substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level, or ■ otherwise substantially degrade water quality. Impacts and Mitigation Measures Impact GW-1 : Operation-Related Impacts on Groundwater Quality (Less than Significant with Mitigation Incorporated) Dry Pit Because the proposed Project involves mining below groundwater level,project- related contaminants could degrade groundwater. Aquifers act as natural filtering mechanisms, in which contaminants bind to the aquifer material and are thus removed from the groundwater. These contaminants may include both organic and mineral constituents,as well as microbiological organisms that could affect the potability of groundwater. The primary contaminant that would be generated through the mining process is suspended sediment. The aquifer would be expected to effectively filter out sediment so that downgradient contamination would not be a concern. Over time, however,sediment could clog the pore spaces of the aquifer,reducing — recharge and transmissivity in the aquifer and thereby diminishing downgradient groundwater levels. Other contaminants that could reach the aquifer include those commonly used in mining operations, such as fuels,other petroleum hydrocarbons,and solvents. The release of such chemicals to the aquifer system could exceed the aquifer's natural treatment ability,resulting in contamination of downgradient wells. This DeSilva Gates Quarry Project -' Draft Environmental Impact Report 3.H-6 As 05105.05