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4. ENVIRONMENTAL ANALYSIS 4.8 HYDROLOGY AND WATER QUALITY overburden within the mined phases as part of the reclamation. These activities would alter,to — some degree,infiltration of precipitation and surface water flows,as described below. Within an active mining phase,stripping away overburden to expose the aggregate for mining would increase surface water infiltration because the surface water would not he impeded by fine-gained overburden soils and without the overburden,the travel distance to the water table would be shorter allowing higher infiltration rates. — When silt ponds are established and a layer of silt forms on the bottom of the pond, infiltration of surface water in silt pond areas would be nearly eliminated. This would also be the case after — mining is competed and the silt ponds are capped. The maximum total surface area occupied by the silt ponds throughout the life of the project(approximately 99 acres)is 15 percent of a total disturbed area of approximately 659 acres. The removal of 99 acres from a total available — infiltration area of 659 acres would be inconsequential and would likely not generate a measurable change in recharge or groundwater levels in wells. Upon implementation of reclamation within the mined phases, the previously removed overburden would be reused to line the bottom of the reclaimed phase. These areas would be used for agricultural cultivation and possibly livestock grazing. By removing the overburden, _ the natural structure of the soil is lost and when it is replaced and compacted, the soils exhibit an altered structure. Under some conditions,this altered structure,especially if compacted, could reduce infiltration leading to reduced water table recharge. This is especially the case in areas where overburden is replaced and engineered to support structures,however,this is not proposed under the proposed project site. The project applicant proposes to replace the overburden and compact it with heavy equipment but does not propose to engineer the fill for structural support. Because the overburden soils are the same as those originally removed and they would not be re- engineered and excessively compacted,the infiltration capacity and permeability of the soils — would not significantly restrict recharge. The active aggregate excavation operations,the use of silt settlement ponds,and the reclamation — of completed mining phases would alter the natural infiltration capacity and permeability of the surface soils but as discussed above,these changes would not significantly change the ability of the soils to infiltrate surface water and contribute to the recharge of the underlying water table. The impact of reduced infiltration and recharge would remain less-than-significant. Mitigation Measure: No mitigation is required. Impact 4.8.6: Mining out Hospital Creek and constructing a berm to form a large detention basin(Mining Plan Option 2)would substantially alter the natural hydrology of Hospital Creek. This option would permanently remove surface water flows from the reach of Hospital Creek downstream of the proposed mining operations leading to depletion of flows to downstream receiving water bodies,reduction of surface water RMC Pati&Vernalis Quany Mining and Reclamation Project 4.8-32 FSA/203015 Administrative Draft E1R Mash 2004