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4.Environmental Analysis area surface streams and agricultural drainages have high total dissolved solids(TDS),and elevated concentrations of nutrients,pesticides, and salinity(RWQCB, 1983). As part of a regional analysis of water quality,the RWQCB tested the surface water in Ingram — Creek and Hospital Creek for the agricultural pesticide diazinon. Consequently,recent reports by the RWQCB lists Ingram Creek and Hospital Creek as an impaired water body due to the presence of the pesticide-related chemicals chlorpyrifos and diazinon in agricultural return flows. Regardless, Hospital Creek and Ingram Creek are considered a low priority for future Total Maximum Daily Loads (TMDL)designation for agricultural chemicals(CVRWQC,2002). Water quality in the major aqueducts and other water supply conveyance facilities is monitored — regularly and is maintained at high standards due to the co-mingling of surface water and groundwater in the downstream San Luis Reservoir system operated by the U.S. Bureau of Reclamation (USBR). Groundwater Hydrology For the purposes of this EIR,information regarding the water bearing units and groundwater hydrology was derived from: • Water level monitoring data from the Department of Water Resources Water Data Library,Groundwater Level Data(California Department of Water Resources [DWRj,2004), • Bulletin 118,San Joaquin River Hydrologic Region, California's Groundwater (DWR, 2003a), • Reclamation Plan for the Applicant for RMC Pacific Vernalis Quarry (Spinardi Associates, 2002), • Preliminary Geological/Geotechnical Study for Quarry Pit Excavation(Geomatrix, 2002),and • Hydrologic study completed on the property adjacent to the southern boundary of the proposed project site(James M. Montgomery Consulting Engineers (JMM) 1993). The Sacramento/San Joaquin Valley is underlain by a large groundwater aquifer known as the Central Valley Regional Aquifer System. The southern two-thirds of this aquifer system,known as the San Joaquin Valley Basin(DWR, 1975),covers 13,500 square miles from the Delta to — Bakersfield.The California Department of Water Resources(DWR)further divides this basin into numerous smaller units called sub-basins. Sub-basins in the northern half of the San Joaquin Valley Basin include the Tracy,Eastern San Joaquin County,Modesto,Turlock,Merced, — Chowchilla,Madera, and Delta-Mendota sub-basins(DWR, 1994).The Tracy and Delta-Mendota Sub-basins lie beneath the proposed project site with the boundaries defined by the Coast Range and Diablo Range on the west;the Mokelumne and San Joaquin Rivers on the north;and the San 5 Total Maximum Daily Load(TMDL)is a determination of the capacity of a water body to assimilate certain — pollutants.TMDLs will eventually become an integral part of surface water quality regulation.The RWQCB is currently deterrnining TMDLs for high priority water bodies in California. RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.84 ESA 1203015 Draft Environmental Impact Report May 2006