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California 1 :conal Water Qualit31.'_,._itrol Board <br /> Central Valley Region <br /> Winston H.Hickox Steven T.Butler,Acting Chair Gray Davis <br /> Secretaryfor Governor <br /> Environmental Sacramento Main Office <br /> Protection Internet Address: http://www.swrcb.ca.gov/-rwgcb5 <br /> 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> TO: Gordon L. Boggs FROM: Mark List <br /> UST Program Manager Engineering Geologist <br /> DATE: 11 March 1999 SIGNATURE: <br /> SUBJECT: NON- CONCURRENCE ON"NO FURTHER ACTION REQUIRED <br /> WATERLOO SHELL, 4315 WATERLOO ROAD, STOCKTON, <br /> SAN JOAQUIN COUNTY <br /> At the request of the San Joaquin County Environmental Health Division (SJCEHD), a file review was <br /> completed to determine if Regional Board staff agree with the SJCEHD determination of no further <br /> action required at this site. The following information was obtained during my review of the Regional <br /> Board and San Joaquin County case files for the Waterloo Shell site. <br /> BACKGROUND: <br /> During December 1994, four underground storage tanks, including one 5,000-gallon, one 7,000-gallon, <br /> and one 8,000-gallon unleaded gasoline tanks, and one 5,000-gallon regular gasoline tank were removed <br /> from the site. Odor and discoloration were noted in the tank pit and below the dispenser and product <br /> lines. The tank pit was overexcavated to approximately 18 feet below ground surface (bgs) and new <br /> double walled fiberglass tanks were installed in the same excavation. <br /> Based on soil sample analytical results, San Joaquin County required an investigation to define the <br /> extent of soil contamination at the site. On 21 February 1996, ten soil borings were advanced onsite <br /> ranging in depth from 8 to 37 feet bgs. MTBE was detected at 30 feet (in SB-1) and 21 feet bgs <br /> (in SB-2, approximately 15 feet east of SB-1) in a sand unit(described as SP -poorly graded sand) at <br /> concentrations of 3.3 mg/kg and 15 mg/kg, respectively. Both samples were collected from the bottom <br /> of each borehole in a highly permeable unit. MTBE was identified in four of the ten soil borings. TPHg <br /> and BTEX constituents were detected in 5 of the 10 soil borings and as deep as 37 feet bgs (the deepest <br /> soil boring onsite). Based on conservative residual contaminant volume estimates, approximately <br /> 344-gallons of TPHg,between 0.016 and 0.027-gallons of benzene, and 2.61 gallons of MTBE remain in <br /> soil below the site. <br /> No groundwater investigation or sensitive receptor survey was ever conducted for the Waterloo Shell <br /> site. Groundwater is present approximately 60 feet below ground surface, and based on the porous <br /> subsurface soils and the nature of MTBE, there is potential for water quality impact from the former <br /> USTs. Groundwater is the primary source of drinking water for area residents and approximately 40 to <br /> 60 domestic wells are located within 2,000 feet of the site boundaries (based on a limited well survey <br /> conducted for a nearby UST site). The closest well in the expected downgradient direction is a <br /> residential well approximately 700 feet east-northeast of the site with a reported screen interval from <br /> 150 to 200 feet bgs. <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br />