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4. ENVIRONMENTAL ANALYSIS 4.8 HYDROLOGY AND WATER QUALITY As shown on the drawdown curve in Figure 4.8-7,for a pumping rate of 2,600 gpm the potential drawdown at a distance of 500 feet could reach 15 feet and at a rate of 6,200 gpm the potential drawdown could reach 36 feet. Based on this extrapolation,a drawdown of 11 and 27 feet is projected at a distance of 1,000 feet with pumping rates of 2,600 and 6,200 gpm,respectively. These results indicate that under full groundwater pumping,the aquifer would respond causing some degree of drawdown. The pumping rates 2,600 and 6,200 gpm assume that the proposed mining operation would be obtaining its entire water supply from groundwater and processing between 1.7 million tons per year(mty)and 4 mty of aggregate material. As discussed above,the project would be using — groundwater exclusively in the interim period while mining operations are underway simultaneously with the construction of the silt ponds. These pumping rates would he a temporary condition and the project would begin using recycled surface water after the silt ponds are constructed and an adequate water supply is contained within. Therefore, the pumping rates and associated drawdown represent temporary conditions. Under normal operations, when the project is using 25 percent groundwater to supplement their surface water supply, the pumping rates and the resultant well draw down would be much lower. Conclusions of Groundwater Drawdown Analysis The results of the 1993 MWA analysis and the application of that data to proposed groundwater pumping conditions do not represent the actual,expected groundwater drawdown at the proposed pumping rates. Rather,they suggest that under the known aquifer conditions and proposed pumping rates,there could be a potential localized drawdown that could adversely impact certain neighboring wells. The maximum drawdown of the local groundwater wells would be realized during the temporary period that the project is using groundwater exclusively for supply. Once the silt ponds are established and recycled water becomes the primary water _ supply,groundwater use would constitute 25 percent of the supply and groundwater withdrawal would decrease. Despite this reduction in groundwater use, supplying 25 percent of the required demand through groundwater would require constant operation of the three onsite supply wells and could result in a long term change to local groundwater levels. The proposed project would cause an increase, over existing conditions, in groundwater pumping at the site and therefore,a potential exists for impacts related to the depletion of water resources. In accordance with the Significance Criteria presented above,this impact is significant. This EIR has developed the mitigations presented below to ensure that the significant impacts related to groundwater drawdown remain less-than-significant. Mitigation Measure 4.8.4x: Single Well Pumping Testing V Prior to commencing mining operations,the project applicant shall complete a single well pumping test on those supply wells intended for extraction during mining operations. The objective of this well test is to evaluate the ability of the supply well(s)to maintain the discharge rate desired for the proposed operation and to determine a time-drawdown relationship. The — RMC Pacific Vanalis Quarty Mining and Re Il uon Prcgmt 4.8-28 ESA/2M]5 Adn innnunw D=ft Eai Murb 2004