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4. ENVIRONMENTAL ANALYSIS 4.8 HYDROLOGY AND WATER QUALITY — obtained from state and federal water projects. Local pumping wells (those within approximately 2 miles)are currently extracting groundwater from the similar aquifers, and consequently,increased pumping within this system could lower local groundwater levels and reduce or eliminate available groundwater for other local users. Adverse impacts of a significant — decline in groundwater levels are realized when the groundwater level is lowered below the level of the down-well pump or in some cases,below the depth of the wells. Significant groundwater extraction from lower confined zones can lead to declines in the water table depth that can affect biological resources by lowering groundwater below the root zone of certain vegetation types or by drawing down water available to vernal pools and wetlands. / Groundwater Impact Analysis D.FM Groundwater resource and availability studies were not completed for the proposed project prior — VU�• ,U to the preparation of this EIR and therefore, site-specific groundwater data is not available regarding the yield of the existing supply wells and the resulting aquifer response under the proposed groundwater pumping scenarios. Accordingly,the impact analysis for this EIR relies — on a groundwater supply study completed by Montgomery Watson Americas, Inc(MWA)in Jp9 1993 for a similar gravel mining project proposed by Granite Construction Company(GCC).l I The previously proposed GCC mining project was to be located south and adjacent to the currently proposed project site but was ultimately not implemented. The GCC mining project was similar to the proposed project because,in addition to its location adjacent to the project site, it also proposed to mine aggregate material up to a depth of 100-foot depth. Further GCC proposed that 20 percent of the water demand for processing was to be supplied by groundwater from the two onsite agricultural wells. Because�f this similarity dat frnm Lhe GCC analysis can generally annly to the proposed project site and can be used to evaluate the potential for project-related impacts associated with the depletion of groundwater — resources. For its study,MWA obtained for analysis,regional and local hydrogeologic data including _ information on geology,groundwater levels and trends,soil conditions,groundwater recharge and aquifer properties. The MWA study included a regional groundwater well inventory that identified a total of 17 groundwater wells within the vicinity of the proposed site including nine domestic wells,seven irrigation wells,and one industrial well. As shown in Table 4.8-2,there are 10 groundwater wells located within 6,000 feet of the project site. Seven of these wells, including two wells located at the project site, are constructed in the lower confined aquifer at depths of 310 and 770 feet below the ground surface(see Table 4.8-2) and withdraw groundwater from common aquifers or water-bearing zones. The agricultural groundwater wells located on the project site are constructed at depths of 630 feet and 470 feet and DWR records indicate that the three existing onsite agricultural wells extract water from confined aquifer below the Corcoran Clay. 11 The report on the groundwater analysis for the previously Granite Construction Company is available for review at the County Planning and Community Development Department. RMC Pacific Vernalis Quany Mining and Reclamation Pmjecl 4.8-26 ESA 1203015 Admwisrtadve Dmft E0[ Mach 2004