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� v o A S S O C I A T E S I N C The site is in the Eastern San Joaquin County Groundwater Basin (California Department of Water ' Resources, 1980) According to the San Joaquin Flood Control and Water Conservation District, the direction of regional groundwater flow is generally to the east The groundwater basin has been developed for intensive irrigation, domestic, industrial, municipal, and stock use There is one surface stream near the site, the eastward extension of the Stockton Deep Water ' Channel (including MacLeod Lake) approximately 1,000 feet to the southwest The Stockton Deep Water Channel empties into the San Joaquin River approximately 2 miles downstream from the site 223 Site Geology and Hydrogeology Based on information obtained from previous borings at the site, sediments underlying the site consist primarily of clay from ground surface to approximately 11 to 17 feet below ground surface (bgs) From 11 to 17 feet to approximately 35 feet bgs, the sediments consist predominantly of sand and silt, with some clay layers Soil boring logs are contained in Appendix A and cross section locations and geologic cross sections depicting the interpreted subsurface conditions are shown on Figures 4, 5, and 6, respectively During groundwater monitoringactivities conducted on December 31 200 1, groundwater was ' encountered at approximately 24 feet bgs From July 1997 to December 2001, static water levels have fluctuated from approximately 20 to 29 feet bgs, variations in depth to water between the wells during each monitoring event are apparently due to seasonal fluctuations and possible hydraulic influence caused by the Stockton Deep Water Channel which is located approximately 1,000 feet to the southwest Based on groundwater elevations measured on December 31, 2001, the direction of groundwater flow is generally toward the northeast at an approximate gradient of 0 007 ft/ft The groundwater gradient map for December 31, 2001 is shown on Figure 3 The direction of groundwater flow has ranged from east to northeast since groundwater monitoring was initiated in July 1997 3.0 PREVIOUS ENVIRONMENTAL WORK ' On January 21, 1988, Falcon Energy, attempted to remove all VOC contaminated soil b p y overexcavating the former tank locations The former tank locations were excavated to a depth Iof approximately 22 feet bgs The excavation was limited to the north by the on-site building The confirmation samples collected from the base of the overexcavation still contained elevated ' concentrations of volatile organics The overexcavated soil was disposed of at Forward Landfill On June 30 and July 1, 1997, Smith Technology personnel supervised advancement of seven soil borings, SB 1 through SB7, at the site to depths ranging from approximately 40 to 45 feet bgs at the site to investigate the horizontal and vertical extent of petroleum hydrocarbon soil and ' w Iwordpro1625961reponsloff--site doc 2