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15 November 2019 AdvancedGeo AGE Project No. 19-4912 Environmental Page 5 of 14 4.0. GROUNDWATER INFORMATION - REGIONAL HYDROGEOLOGY The Geologic Map of California, published in 1966 by the California Department of Conservation Division of Mines and Geology, shows the site area within the Great Valley Syncline (GVS), a large, elongate, northwest trending structural trough. The GVS is subdivided into two major divisions designated the Sacramento and San Joaquin Valleys, which have been filled to the present elevation with thick sequences of sediment ranging in age from Jurassic to present day, creating a nearly flat-lying alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively. Geologically, the area around the property generally consists of Holocene-aged flood-basin deposits of clay, silt, and sand. Miocene to Holocene age-units are located in the surrounding area. These deposits are heterogeneous mix of generally poorly sorted clay, silt, sand, and gravel with some beds of claystone, siltstone, sandstone, and conglomerate (1986). Most of the fresh groundwater in the Central Valley is contained in the post-Eocene-aged continental rocks and deposits and in the Holocene-aged river deposits consisting of gravel, sand, silt, and minor amounts of clay. In general, these geologic materials comprise a major widespread aquifer extending hundreds of feet deep and occasionally containing individual confining layers. The Modesto, Riverbank, Turlock Lake Formations and overlying recent alluvium are the principal source of domestic groundwater in the 13,500-square mile San Joaquin Valley Groundwater Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River, which is approximately 2.6 miles west of the subject property and is the nearest surface water feature to the site. 4.1. GROUNDWATER DESCRIPTION FOR THE GENERAL AREA According to the San Joaquin County Flood Control and Water Conservation District's Lines of Equal Depth to Groundwater Fall 2018 and the Department of Water Resources (DWR) Water Data Library, depth to groundwater at the site is approximately 25 to 30 feet below surface grade (bsg). Between 2011 and 2018, depth to groundwater at the site has fluctuated between 20 and 30 feet bsg. Groundwater flow direction locally appears to be toward the northeast. Groundwater was not encountered in the 42-inch deep percolation test hole advanced on 13 November 2019. 4.2. GROUNDWATER CONTAMINATION IN THE AREA OF THE SITE The immediately adjacent and outlying land use for the parcel is residential, agricultural and vacant. Potential groundwater contamination can occur from several sources including leaking underground storage tanks, septic systems, agricultural activities, dairies, and stormwater infiltration.