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MEa <br /> June 25, 1991 <br /> ARCO Service Station 750, Lodi, California <br /> Initial estimates of the effective radius of influence of 22 feet from each vapor extraction <br /> well were made using a vacuum of 30 inches of water column, a flow rate of 50 cmf, an <br /> initial TPHg concentration of 10,000 mg,J.,.}, and the duration of operation of'a vapor <br /> extractions system of 12 months. This estimate of the radius of influence can be further <br /> refired as the subsurface environmental investigation progresses. The location and screened <br /> interval of subsequent vapor-extraction wells will be based on this refined data. <br /> Conclusions <br /> Low levels of residual hydrocarbons were detected in the proposed tank cavity. Results of <br /> the vapor-extraction test indicate the use of vapor extraction at this site is a practical and <br /> efficient chore as a soil remediation alternative. <br /> At the request of ARCO, we will observe the installation of six conductor casings in the <br /> locations shown on PIate 2 before the tanks are installed. These conductor casings will <br /> allow soil borings to be drilled between the new tanks at a later date to delineate the <br /> residual hydrocarbons. After the residual hydrocarbons are delineated vertically and <br /> laterally, vapor-extraction wells can be installed between the proposed tanks to <br /> remediate the soil if warranted. <br /> ARCO is requesting authorization to install the new tanks in the proposed tank cavity as <br /> planned. No remediation will be conducted until we submit 4 Remedial Plan to your agency <br /> and the plan is circulated for a 30-day public review. <br /> r _ <br /> t 06Uctre 4 <br /> 380483 <br />