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Ic o W�s A S S O C I A T E S I N C In March 1999, ATC personnel supervised the advancement of three soil borings at the site Drilling was pg ormed by V,.&W Drilling using hollow stem auger One soil boring was advance ef�anl d twcI bogs•were advanced on site Grab groundwater samples from two of the soil borings contained detectable concentrations of petroleum hydrocarbons One on- site soil boring was advanced to approximately 65 feet_bgs to define the vertical extent of ' impacted soil The results of the site investigation` were detailed in ATC's Summary Report of Soil and Groundwater Investigation, at 610 North Hunter Street, Stockton, California, dated July ' 16, t999 2.0 SUBSURFACE CONDITIONS 221 Regional Geology and H,ydrogealogy ' The site is underlain by the Modesto Formation, which is divided into nonmarine basin deposits, fan deposits, and stream channel deposits consisting of clay, silt, and sand (Rogers, 1966) Basin deposits are dominant at this site The Modesto Formation dips gently to the west (Wagner, et al , ' 1981) 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 ' 2.2 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 bgs From 1 I 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 monitoring activities conducted on June 8, 2000, groundwater was encountered at approximately 21 feet bgs From July 1997 to July 2000, 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 W 1625961reportslpilotcap doc 3