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30 July 2019 AdvancedGeo • AGE Project No. 19-4772 Lr-ivironmentol Page 5 of 14 0,.iM I 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 three miles west of the property. The nearest surface water features near the property is the Old River located approximately 2.25 miles northwest of the property. 4.1. GROUNDWATER DESCRIPTION FOR THE GENERAL AREA The San Joaquin County Flood Control and Water Conservation District's Lines of Equal Depth to Groundwater Spring 2018 indicates the depth to groundwater is approximately 30 to 40 feet below surface grade (bsg). Groundwater flow direction locally appears to be toward the southeast. Groundwater was not encountered in the percolation test holes on 12 and 24 July 2019. 4.2. GROUNDWATER CONTAMINATION IN THE AREA OF THE SITE The immediately adjacent and outlying land use for the parcel is residential; agricultural land use begins approximately 0.25-miles north of the property. Potential groundwater contamination can occur from several sources including leaking underground storage tanks, septic systems, agricultural activities, dairies, and stormwater infiltration. A review of the California Department of Toxics and Substance Control (DTSC) EnviroStor Database and the Geotracker Web site did not reveal any sites of environmental concern within a half-mile radius of the site. 4.3. ON-SITE EXISTING WELL DESCRIPTION There is one existing out of service water supply well on the property. The well was installed in May 1977 under_EHD permit number 77-544W (Appendix B). The well is constructed with a 6-inch diameter casing antl a grout seal to 50 feet; the total depth and screen interval of the well is unknown. Currently, a pump is not installed in the well and it's not connected to a pressure tank. The well is not used as a water source at the property. The existing potable water service is provided by the City of Tracy and the service has been provided since 2007. 5.0. SOIL PROFILE An OWTS Permit was issued for the property by the EHD on 25 June to perform a percolation test; the permit was updated on 17 July 2019 to perform an additional