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SUBSURFACE SOIL AND GROUNDWATER ASSESSMENT REPORS TOPOGRAPHY AND HYDROGEOLOGY The USGS Stockton West, California 7 5 minute quadrangle, edition of 1968, indicates the site is relatively level with an elevation of approximately 8 to 9 feet above mean sea level (amsl) The 1 surface gradient as shown on the topographic map appears to be in a northeasterly direction No watercourses or lakes are depicted on or immediately adjacent to the site The Calaveras River is located approximately 1,800 feet north of the site The condition of the site with respect to ' aquicludes, and perched water zones has not yet been determined Site hydrologic characteristics were obtained from Ground Zero Analysis, Inc and information ' gathered during this recent assessment 1 The site is located in the San Joaquin Valley, within the Great Valley Geomorphic Province Based on the soil materials encountered during UST removal, and the recent assessment, shallow soil underlying the site consist generally of brown ' clayey silt and fine sand (see Soil Boring Logs,Appendix A) The water table is present in these fine-grained alluvial materials at depths ranging from approximately 15 to 20 feet Groundwater was not encountered in the 13-foot deep excavation needed for the UST removal Based upon surface topography and the location of the Calaveras River, estimated groundwater flow of the water table is north-northwest towards the Calaveras River Regional flow of groundwater, as determined by groundwater wells penetrating deeper water-bearing strata,can vary in this area but is generally easterly, towards a groundwater depression beneath the City of Stockton 2 Thirteen municipal groundwater wells have been identified from 2000 feet to 5600 feet from the site (refer to Table 3 and Figure 3) Two of the wells are owned by UOP and the other 11 wells are owned by the California Water Service The City of Stockton,Department of Municipal ' Utilities does not have any wells within one mile of the site (Ed Formosa, City of Stockton, 2000) Well construction data on the two wells owned by UOP was provided to ESA That data indicated that the well located at Pacific Avenue at Brookside Road(referred to as the Pharmacy Well#3) is 510 feet deep with the highest perforation at a depth of 225 feet bgs Water level in 1 this well is 55 feet bgs According to the well log, the shallow groundwater(water table)is separated from the lower, possibly confined groundwater—bearing zones by over 70 feet of clay "hardpan" soils Another UOP well (referred to as Burns Tower, Well#2) is located on Pacific LAvenue between Fulton and Knoles Streets This well is 502 feet deep with the highest perforation at a depth of 130 feet bgs The water table in this location is separated from the lower groundwater bearing strata by about 35 feet of brown clay The clay unit in this area (extending ' from approximately 40 to 110 feet) is expected to form a relatively impermeable aquitard that would diminish a vertical groundwater gradient between the water table and lower source aquifer 1 Underground Storage Tank Closure Report, 1081 W Mendocino Avenue,Stockton,California,April 26,2000, prepared by Ground Zero Analysis,Inc 2 San Joaquin County Flood Control and Conservation District, Groundwater Report,Spring and Fall 1998 Subsurface Soil and Groundwater Assessment ESA/200252 ' 1081 w Mendocino Avenue Stockton,California 6 August 25,2000