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4.8 Hydrology and Water Quality 4.8 Hydrology and Water Quality 4.8.1 Introduction This chapter describes the hydrologic and water quality characteristics of surface water and groundwater resources on and near the proposed project site and focuses on the effect that a large ` aggregate quarry operation and its eventual reclamation would have on those resources. The setting portion of this chapter presents existing conditions by describing the climate, surface water and groundwater conditions, and water quality issues.The Regulatory Background section describes the pertinent federal, state, and local laws related to the hydrology and water quality of a surface mining operation. The Impacts and Mitigations section defines the significance criteria, presents discussion of the impacts, and where necessary,applicable mitigation measures. 4.8.2 Setting Surface Water Hydrology ` The San Joaquin Valley has hot, dry summers and relatively mild winters. The average annual rainfall ranges from 5 to 16 inches, with most of the rainfall occurring from November through April. The average annual rainfall is approximately 10 inches at the proposed project site and increases to 12 inches in the contributing watersheds to the west. The most intense 1-day storm, referred to as the 100-year storm, is estimated at approximately three inches (NOAA, 1973).1 As ` a comparison, the 100-year, 24-hour precipitation event for the city of Sacramento is over four inches of rainfall. r The Sacramento/San Joaquin Valley is a broad structural basin bordered by the Sierra Nevada on the east and the Coast Ranges on the west. The northern portion of the San Joaquin Valley drains toward the Delta by the San Joaquin River and its tributaries, the Fresno,Merced,Tuolumne,and r Stanislaus Rivers. The southern portion of the valley is internally drained by the Kings, Kaweah, Tule, and Kem Rivers that flow into the Tulare drainage basin that includes the former Tulare, Buena Vista, and Kem Lakes. The 688-acre proposed project site is situated on the Hospital Bar alluvial fan, located along the western margin of the San Joaquin Valley. Surface drainage flows eastward toward the valley floor but some natural flows infiltrate into the ground prior to reaching the San Joaquin River, The Lone Tree Creek watershed, Hospital Creek watershed,and Ingram Creek watershed contribute surface water flows to the project site and adjacent areas. Average annual runoff estimates for these watersheds are presented in Table 4.8-1. Surface water flows near the project site fluctuate seasonally, with precipitation and decreased evaporation in winter, and little to no rainfall and increased evaporation in summer and fall. Due to the small amount of annual rainfall 1 The 100-year storm event is the event that has a 1 percent chance of being equaled or exceeded in any given year. RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.8-1 ESA 1203015 Draft Environmental Impact Report May 2006 r