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23 October 2019 AdvancedGeo AGE Project No. 19-4881 E ri v i ro ri m e n t a l Page 5 of 15 3.6. PROPOSED MAXIMUM SEPTIC TANK USAGE ON SITE The current single-family residence on the property has two (2) bedrooms and utilizes the existing septic system installed in 1961 under EHD permit number 13283 and improved in 2017 under EHD permit number SR0078110. The existing residence is currently vacant, but the septic system will eventually be used 365 days per year. The existing septic system will not be altered from the current configuration. The average and reasonable maximum usage of wastewater for a two-bedroom home by residents is 140 gallons per day (gpd) per bedroom for a total of 280 gpd. The new proposed septic system is planned to be located in the southeastern portion of the property over 150 feet away from the onsite water well. The proposed septic system will service the planned modular two-bedroom residential home to be developed on the property. The proposed septic system will be used by the two-bedroom residence 365 days per year. The average and reasonable maximum usage of wastewater for a two- bedroom home by residents is 140 gpd per bedroom for a total of 280 gpd. 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 1.4 miles west of the property and is the nearest surface water feature near the site.