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Ms Laurie Cotulla <br /> April 29, 1992 <br /> Page 2 <br /> The effluent vapors from the treatment system will be sampled and analyzed on a regular basis, <br /> (as specified in the APCD air permit) to ensure air emissions remain within regulatory <br /> compliance In addition the hydrocarbon concentrations in the extracted vapors will be monitored <br /> and the vapor extraction rate will be adjusted, as needed When hydrocarbon concentrations have <br /> decreased significantly the treatment process may be modified to utilize granular activated carbon <br /> (GAC) as an air pollution control device instead of catalytic oxidation <br /> INTRODUCTION <br /> This addendum to the draft FRP for ARCO Station 2133 (site) located at 2908 West Benjamin <br /> Holt Drive,Stockton,Cahfonia, addresses soil conditions at the site The preparation of the FRP <br /> is required by the County BCC's July 11, 1991, draft FRP addressed the groundwater conditions <br /> at the site The FRP is organized based on Appendix A of the Tri-Regional Board Staff <br /> Recommendations for Preliminary Evaluation and Investigation of Underground Tank Sites The <br /> location of the site is shown on Figure 1 <br /> There are 15 groundwater monitoring wells and one groundwater extraction well located on, or <br /> in the vicinity of, the site A groundwater extraction system has been operating at the site since <br /> June 1991 Figure 2 shows the location of the monitoring wells and extraction well <br /> SITE CONDITIONS <br /> This section provides a bnef description of lithology and describes the soil quality and the results <br /> of the soil vapor extraction pilot testing <br /> Lithology <br /> ARCO Station 2133 is located in the northwestern portion of the city of Stockton The site is , <br /> ,underlain by a series of interbedded silt and clay with discontinuous sand lenses , Presently, <br /> 'graundwater occurs at a depth of approximately 17 to 18 feet below ground surface (bgs) <br /> BCC's June 10, 1987, Problem Assessment Report (PAR) contains a detailed description of the <br /> regional and site geology <br /> Soil Quality <br /> This evaluation of soil quality at ARCO Station 2133 is based on BCC's 1987 investigation <br /> . (which included drilling seven soil boreholes), soil samples collected during the September 1991 <br /> product recovery tank removal and waste oil tank installation, and the results of the March 1992 <br /> vapor extraction pilot study <br /> l;rown and Caldwell 6747gUTORTSY747-04 LTR <br /> Consultants <br />