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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Surface Hydrology,Stormwater,and Water Quality 2004a). The 10-year,24-hour estimated precipitation amount near the project area ranges 1.8-2.0 inches and the 100-year,24-hour estimated precipitation ranges 2.5-3.0 inches(WRCC 2004b). Elevations in the project area range approximately 150-180 feet above mean sea level(msl). Surface Water _ The proposed Project is located within the Middle San Joaquin-Lower Merced- Lower Stanislaus watershed(U.S. Geological Survey [USGS] cataloging number 18040002). Major water bodies in this watershed include the lower Merced River,the lower Stanislaus River, San Joaquin River,Lone Tree Creek, Orestimba Creek,Temple Creek, and Harding Drain(CERES 2003). Surface water bodies near the project area include the Delta-Mendota Canal, the California Aqueduct,and Lone Tree Creek. — The Delta-Mendota Canal,which is adjacent to the southwest portion of the project area,receives flows via the Tracy Pumping Plant. The concrete-and _ earth-lined canal extends 117 miles from the Tracy Pumping Plant to Mendota Pool,located approximately 30 miles from Fresno(Bureau of Reclamation 2005). Currently a maximum of 710 acre-feet per year(ac-ft/yr)is diverted from _ the canal by the Del Puerto Water District and used to support the almond orchard in the project area. The actual quantity of water diverted from the canal may be substantially less than 710 ac-ft/yr because it is adjusted annually based on projected water supplies. Water bodies are not present within the project area boundaries. The nearest water body is the Delta-Mendota Canal, which borders the western portion of the project area. The project area is located in an area with minimal flooding and is outside the 100-year floodplain(the area with a I%chance of flooding in any given year)(FEMA 2002). Runoff in the project area generally flows to the — northeastern comer of the project area, where it likely collects in a depression and does not flow off-site. Runoff from SR 132 may drain to the project area but would collect in the northwestern depression and not travel off-site. Flows from the remaining surrounding area do not enter the project area. Water Quality _ Surface Water Quality. Most of the project area is being used as an almond orchard and is surrounded by orchards,row crops, and a few residences. Non- point-source runoff from agricultural areas is characterized by contaminants such — as nutrients(particularly nitrogen and phosphorus), sediment,pesticides, and salts(EPA 1993). In general,the water quality of the Delta-Mendota Canal is very good and meets all primary and secondary maximum-contaminant levels(MCLS) for drinking water quality(DWR 2000). The water quality of the Delta-Mendota Canal is not listed by the State Water Resources Control Board (State Water Board)as The 10-year,24-hour precipitation estimate refers to the approximate amount of rainfall that is expected to fall _ over a 24-hour period during a 10-year storm event or an event that has a 10%probability of occurring during a normal year. DeSilva Gates Quarry Project — Draft Environmental Impact Report 3.G-2 As 05105.05 —