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1 <br /> • Antrol Board <br /> California Regional Water Quality -> <br /> Central Valley Region � <br /> Robert Schneider,Chair Grav Davis <br /> Winston H.Hickox Governor <br /> Secreta,y for Sacramento Main Office <br /> Environmental Internet Address: http://Nvw%v.swrcb.ca.gov/—rwgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> 8 October 2003 <br /> Mr. William Moranda <br /> c/o Mid-Valley Construction <br /> Former Buffalo Tank Corporation <br /> 5709 East Highway 26 <br /> Stockton, CA 95204 <br /> ADDITIONAL SITE INVESTIGATION WORK PLAN, FORMER BUFFALO TANK <br /> CORPORATION, 5709 EAST HIGHWAY 26, STOCKTON, SAN JOA QUIN COUNTY <br /> I reviewed the Additional Site Investigation Work Plan (Workplan), dated 30 September 2003, submitted <br /> on your behalf by Advanced GeoEnvironmental, Inc. (AGE). The Workplan proposes further <br /> investigation of the lateral and vertical extent of contamination, using a hollow stem auger dri11 rig to <br /> collect soil and grab groundwater samples during two mobilization phases. Phase One of the Workplan <br /> would involve sampling soil from three borings located a) between the former Underground Storage <br /> Tank(USTs), b) under the dispensers, and c) 25 feet north of USTs Tank 1. If unspecified levels of <br /> contamination were verified in the field, then the three borings would be completed as monitoring wells. <br /> Grab groundwater samples would be collected below the augers using a Hydropunch® tool, or by a <br /> disposable bailer dropped into the open augers, after disconnecting the drill rig drive head. If <br /> contamination is not detected in the field, then the three borings would be abandoned, grouted up, and no <br /> further investigation (Phase 2) would be conducted. The two optional borings/well completions would <br /> be installed during a second mobilization (Phase 2), if deemed necessary by AGE after reviewing the <br /> Phase 1 sampling data and one onsite private supply well data(located 80 feet from the USTs). The <br /> Workplan states that quarterly groundwater monitoring and reporting would be conducted if monitoring <br /> wells are installed. The Workplan reported that the depth to groundwater in the onsite private supply <br /> well was 77 feet bgs during a reconnaissance site visit completed in September 2003. <br /> In a July 1993 Condor Earth Technologies (Condor Report) described the overexcavation of the USTs, <br /> and soil sampling results from five confirmation samples taken between 17 feet and 22 feet below <br /> ground surface (bgs) from both USTs (Tanks 1 and 2). The Condor Report revealed high levels of <br /> contamination left in place. Maximum reported soil concentrations were: mineral spirits as paint thinner <br /> (TEPH, 11,000 mg/kg), toluene (100 mg/kg), ethylbenzene (120 mg/kg), and xylenes (690 mg/kg). <br /> These results were not included in the Workplan. <br /> Soil analysis from a single boring in the AGE Preliminary Site Assessment Report (AGE Report), dated <br /> 26 August 2003, revealed petroleum hydrocarbon contaminations at one of the two USTs locations <br /> (Tank 1). Maximum concentrations were: Total Petroleum Hydrocarbons as gasoline (TPHg, 11,000 <br /> mg/kg), toluene (3.9 mg/kg), ethylbenzene (11 mg/kg), and xylenes (600 mg/kg). Xylenes were detected <br /> in soil down to 40 feet bgs. The boring log from the AGE Report shows a silty, fine sand unit probably <br /> exists between 42 and 52 feet bgs, representing a more permeable zone below the shallower reported <br /> California Environmental Protection Agency <br /> �a Rect,cled Paper <br />