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October 9, 1998 <br /> Mr H Knoll/SJCPHS <br />' page 2 <br /> HydrogeologT <br /> The former facility is within the Central Valley Basm and is less than 1000 feet from the Stockton <br /> Deep Water Channel Depth to groundwater is approximately 25-35 feet below ground surface <br /> Other sites in the area are affected by tidal influences, showing the groundwater gradient towards <br />' the east at the time of momtonng (SJCPHS, 1998). <br /> PREVIOUS WORK <br />' According to Harland Knoll of the San Joaquin County Public Health Services (SJCPHS), three <br /> underground storage tanks were closed in place beneath the sidewalk Vapor extraction was <br /> conducted at the site Upon completion of vapor extraction, site closure was granted in 1995 <br /> (SJCPHS, 1998) <br />' In May 1997, during a property transfer site assessment, four borings were drilled Soil samples <br /> from two of the borings contained petroleum hydrocarbons at 20 and 25 feet Total petroleum <br /> hydrocarbons (TPH) concentrations of 16,200 and 1,160 mg/kg were detected m soil samples at <br /> 20 feet in Borings PB1 and PB2, respectively The highest concentrations of toluene, <br /> ethylbenzene and total xylenes were detected in Boring PB1 at 49.2, 308, and 1,920 mg/kg, <br /> respectively No groundwater samples were collected Due to the concentrations detected during <br /> the property transfer site assessment, the SJCPHS determined that the site required additional <br /> assessment <br /> 1 <br /> 1 <br />