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4.Environmental Analysis L Creek either enters the San Joaquin River Basin through groundwater aquifers or as a contribution to the local surface water flow to the San Joaquin River. In consideration of preserving the natural hydrologic balance of the Hospital Creek, Ingram Creek, and Lone Tree Creek watersheds and 6. their contribution to the regional hydrologic system,eliminating Hospital Creek could result in a long term reduction of critical flows to the San Joaquin River. Because the project under Mining Plan Option 2 would redirect Hospital Creek flows, it would contribute to the cumulative reduction of flows to the San Joaquin River and thus represents a significant impact. The amount of surface water in Hospital Creek that is available for infiltration and groundwater ` recharge is not quantified,but given that Hospital Creek traverses alluvial plain material,its contribution to groundwater recharge warrants consideration. The magnitude of infiltration along the entire course of Hospital Creek varies depending on slope gradient and underlying geologic ` materials. Based on topography,Hospital Creek surface water would likely have higher rates of infiltration and groundwater recharge east of the proposed project. An indicator of reduced groundwater recharge would be a measurable decrease in water levels within the shallow, r unconfined 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. r 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 Measures Measure 4.8.6: The applicant shall implement Mining Plan Option 1 as described in Chapter 3, Project Description, and as shown graphically 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. Impact Significance After Mitigation: Implementation of Mitigation Measure 4.8.6 ` would eliminate the downstream hydrologic issues associated with removing Hospital Creek under Mining Plan Option 2. Implementing 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 °i preferred approach to mining adjacent to Hospital Creek,then the impacts to hydrology,as described above, would remain significant. r RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.8-32 ESA/203015 Draft Environmental Impact Report May 2006