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4. ENVIRONMENTAL ANALYSIS 4.8 HYDROLOGY AND WATER QUALITY - surface water flow to the San Joaquin River. The measured impact of eliminating the flow — contribution from Hospital Creek was not available for this EIR and therefore,the magnitude of impact of reducing flow contribution to the San Joaquin River Basin is not known. However,in consideration of preserving the natural hydrologic balance of the Hospital Creek,Ingram Creek, and Ione Tree Creek watersheds and their contribution to the regional hydrologic system, eliminating Hospital Creek could result in a long term reduction of critical base flows to the San Joaquin River. Because the project under Mining Plan Option 2 could contribute to the — cumulative reduction of flows to the San Joaquin River,eliminating Hospital Creek is a significant impact. The contribution from Hospital Creek of surface water available for infiltration and recharge is not quantified,but given that Hospital Creek traverses alluvial plain material,the potential for infiltration and recharge of the water table warrants consideration. The magnitude of infiltration along the entire course of Hospital Creek would vary depending on slope gradient and underlying materials. Based on topography, Hospital Creek surface water would likely have higher infiltration rates and contribute to the water table recharge east of the proposed project. The contribution to the water table provided by Hospital Creek is not quantified but an indicator of reduced recharge would be a measurable decrease in local groundwater levels in wells — pumping from the water table aquifer. Other consequences of reduced surface water recharge are biological impacts that could occur if water is not available to the root zone of plants due to decreased flows in local surface water. Because of the uncertainty related to the groundwater — contribution of Hospital Creek and the possibility that recharge to the water table east of the site depends at least partly on contributions of surface water,the elimination of Hospital Creek under Mining Plan Option 2 is a significant impact. — Removal of Hospital Creek from within the boundaries of the project site could result in adverse impacts to downstream hydrology and recharge and there is uncertainty as to the magnitude of — these impacts. Because of this, appropriate mitigation for the potentially adverse effects of Mining Plan Option 2 would involve leaving Hospital Creek in its present alignment and not altering its existing flow regime, as presented in Mitigation Measure 4.8.6. Mitigation Measure 4.8.6: The applicant shall implement the Mining Plan Option 1 as described in Chapter 3.0,Project Description of this document and shown in Figure 3-3. Mining Plan Option 1 requires the applicant to leave Hospital Creek in place,mining both sides with a 100-foot setback from the centerline of the creek to the top of the mining slope. Significance atter Mitigation: Implementation of Mitigation Measure 4.8.6 would eliminate the downstream hydrologic issues associated with removing Hospital Creek under Mining Plan Option 2. hnplementing Mitigation Measure 4.8.6 would ensure that significant impacts related to Mining Plan Option 2 would not occur. However,if Mitigation Measure 4.8.6 is not implemented and Mining Plan Option 2 is identified as the preferred approach to mining adjacent to Hospital Creek,then the impacts to hydrology,as described above, - would remain significant and unavoidable. RMC Pacific Vemalis Quany Muting and Reclamation Pmject 4.8-34 PSA/203015 Adm uauve Draft QR March 2004