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4 _ <br /> Geologgtcal?ec(uGics'w. Page 2 <br /> McGranahan{Gawne Road) <br /> Cost Pre-Approvai <br /> Project 251.3 <br /> June 12, 1997._ <br /> part, for the center of highest contaminant mass to migrate away from the source down towards <br /> groundwater. Groundwater monitoring has'not occurred. Mass balance calculations show that <br /> approximately 1,675 gallons of gasoline remain in the subsurface. <br /> Site geologic conditions are dominated by sandy sediments with a thin gravel layer at 63 feet. <br /> The presence of MTBE in the gasoline and evidence of chemical mass transfer through the <br /> subsurface soils away from the ,source suggest that the gasoline contaminant.may encounter <br /> groundwater and potentially,impact the property's domestic well located 200 feet east of the <br /> former tank location. <br /> Summary of Project <br /> On behalf of Mr. Michael McGranahan, trustee in bankruptcy, Geological Technics Inc. has <br /> performed environmental assessment work-at the former Moresco Property located at 16865 <br /> Gawne Road in Stockton. _ <br /> The subject property had a 500 gallon capacity underground storage tank (UST) once used for <br /> residential automotive fuel supply. The UST was removed on November 15, 1994 and <br /> significant concentrations of gasoline range petroleum hydrocarbons were detected in a soil <br /> sample collected beneath the former tank cradle at depth of 17.5 feet below ground surface (bgs). <br /> This information was reported to the San Joaquin County Public Health Services Environmental <br /> Health Division (SJCPHSEHD) in the Geological Technics Inc. Tank Removal Report, 16865 <br /> iGawne Road, dated December 9, 1994. <br /> A subsurface investigation designed to define'the vertical and lateral extent of the impacted area <br /> was proposed in the Geological Technics Inc.''Site Characterization Work Plan dated March 14, <br /> 1995. The Work Plan was approved by the SJCPHSEHD on April 3, 1995'. <br /> An initial subsurface investigation was conducted April 5 to 7, 1995 ,and a remobilization <br /> occurred on April 21, 1995. The results of this investigation indicated that the vertical extent, at <br /> or near the point of release, was defined. The.lateral extent reained undefined to the north and <br /> east. This information was documented in the Geological Tecmhnics Inc. Soil Boring Installation. <br /> Report dated May 12, 1996. <br /> In response to the investigation's findings, SJCPHSEHD directed that .further site <br /> characterization work be performed in their March 27,-1996 correspondence. It was directed that <br /> additional geotechnical, geochemical, and soil gas data be collected from a boring through native <br /> ,_-_Soil,near the.point-of-releaser This additional-mi.fonridtion could-be used-to-evaluate-.the.fate-and _ <br /> transport of the contamination and help determine if it would adversely affect human health or <br /> the environment. <br /> This report documents the site- characterization work 'performed to date and makes <br /> recommendations for modeling the fate an&transport of these chemicals and for evaluating the <br /> risk of leaving these chemicals in the ground for natural attenuation processes to address. <br /> Project Chronology <br /> 11/15/94 500 gallon UST removed <br /> 03/14/95 Submit Site Characterization Work Plan <br /> 0415-7195 Drill S13-1, SB-2,"SB-3, & S134 <br /> r 04/19/95 Submit addendum proposing SB-1A <br /> 04/21/95 Drill SB-1A <br />