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S [EC ® 1R Y . Conceptual Site Model " 5 March 24, 2004 r Page 2 Stratigraphy is relatively consistent across the site The local geology consists of recent unconsolidated alluvial and fluvial deposits to approximately 60 feet below ground surface (bgs) These sediments are a mixture of co-deposited sands, silts and clays, principally sandy-silts and silty-clays Specifically, silt with sand or clay with silt to clayey silt strata to approximately 40 feet bgs, sandy to clayey silt strata from approximately 40 feet bgs to 50 feet bgs, sandy silt to silty strata from approximately 50 feet bgs to 80 feet bgs, sand to clayey slit strata were encountered below 80 feet bgs Generalized geological cross sections are Included as Figures 4 and 5 2 2 Hydrogeology The Site is located in the Eastern San Joaquin County Groundwater Basin Groundwater in the area is for irrigation, domestic, industrial and, municipal use, and stock watering The principle source of groundwater in the area is the Tulare formation The Tulare formation is separated into three zones, the Upper Tulare Aquifer, the Corcoran Clay Layer, and the Lower Tulare Aquifer (USGS, 1998) �r The Upper Tulare Aquifer is generally encountered from approximately 5 feet bgs to 200 feet bgs The Corcoran Clay, consisting of low permeability silt and diatomaceous clay, is generally encountered at 200 feet bgs, has a maximum thickness of approximately 100 feet The Lower ? Tulare Aquifer (confined) lies below the Corcoran Clay No Aquitards or perched aquifers are likely based on regional geology(USGS, 1998) war zs 2.21 Groundwater Flow Rates and Directions Groundwater beneath the site generally flows to the northeast with gradients ranging from approximately 0 004 feet per foot (ftlft) to 0 03 ft/ft Groundwater flow gradient data diagrams showing historical gradient and flow directions are provided for the site and for the ARCO service station (northeast of site) as Figure 6 and 7, respectively = t 2 2 2 Groundwater Use s The San Joaquin groundwater basin underlies the site Beneficial uses of groundwater in the area 1 include municipal, irrigation, stock watering, process and service (SECOR, 2003a) Water wells within a one mile radius of the site and their approximate locations is presented within the EDR GeoCheck@ - Physical Setting Source Addendum, dated January 27, 2004, included in mrt Appendix A -Five supply wells were located between Y4 and y2 mile of the site San Joaquin County municipal water supply wells are typically screened in the Lower Tulare Aquifer 2 3 Surface Water The site is located approximately 2 '/4 miles east of the San Joaquin River, within the San Joaquin River Basin (Figure 1) The California Regional Water Quality Control Board - Central Valley Region (CRWQCB-CVR) defines the San Joaquin River basin as the area drained by the San Joaquin River, including all watershed tributaries to the San Joaquin River, and the Delta south of the Sacramento River and south of the American River Watershed Mormon Slough is located approximately 3,000 feet northeast of the site The Port of Stockton deep water channel is located approximately 1 '/4 miles north of the site I Cliovron192033\REPdRTSICSMICSM 92033(REV B)doc