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URS • Ms Margaret Lagono Page 4 San Joaquin County Environmental Health Department June 27, 2003 April/May 1990 Site Investigation The April/May 1990 site investigation included installing five groundwater monitoring wells (W-lA, ' and W-9 through W-12) (Attachment E) Soil samples were collected from the borings and analyzed for total petroleum hydrocarbons and benzene, toluene, ethylbenzene, and xylenes (BTEX) by Modified EPA Method 8015 Total petroleum hydrocarbons were identified in 12 of the 68 soil samples at concentrations up to 17,000 mg/kg BTEX was identified at the following maximum concentrations benzene, 220 mg/kg, toluene, 1,100 mg/kg, ethylbenzene, 490 mg/kg, and xylene, 3,000 mglkg The highest concentrations were measured in vapor extraction well V4 at 40 feet bgs (B&C, 1990) Groundwater was sampled from wells W-lA through W-12 (excluding W-4) and analyzed for total petroleum hydrocarbons and BTEX by Modified EPA Method 8015 (Attachment F) Certain wells were also tested for fecal coliform Total petroleum hydrocarbons were identified in 11 of the 13 samples at concentrations up to 6 6 mg/1L BTEX was identified at the following maximum concentrations benzene, 30,000 µg/L, toluene, 38,000 gg/L, ethylbenzene, 2,700 µg/L, and xylene, 15,500 µg/L Although fecal coliform tests were positive for two of the five samples analyzed, the low level is j believed to be due to naturally occurring levels of fecal coliform in the soil (B&C, 1990) Quarterly monitoring at this site began in April 1990 and continued through Fourth Quarter 1996 1991 Soil Vapor Extraction and Treatment System After vapor extraction wells V-1 through V-8 were piped to the soil vapor treatment system, the system operation began in 1991 The system was shut down in February 1996 During its operation, the system removed 50,862 pounds (8,203 gallons) of total petroleum hydrocarbons as gasoline (TPHg) and 153 pounds (21 gallons) of benzene from site soil Soil vapor extraction data is included in Attachment F 1992 Groundwater Extraction and Treatment System After extraction well E-1 was piped to the groundwater treatment system, the system operation began in 1992 Monthly samples were collected and analyzed for TPHg and BTEX in both the influent and effluent As of March 1993, all samples were non-detect at or above the reporting limits so the system operations were modified The system was operated one week on, one week off for 2 months believing this flushing action might result in increased concentrations of contaminants in influent water However, monthly samples collected in March and April remained non-detect, and the system was turned off in April 1993 Effluent piping from the Groundwater Extraction and Treatment System was disconnected from the industrial sewer on March 28, 1994 (B&C, 1993) Groundwater extraction and treatment system data is included in Attachment F i K 1WprocessU5 BP ARCO\004341Closure RequesAStation 434 Closure Doc doc