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9 MrqWAAW � <br /> February 10, 1992 Working to Restore Nature <br /> ARCO Station No 2130, Stockton, California <br /> The results of laboratory analvses of the vapor samples indicated that the influent TPHg <br /> concentrations ranged from 43,000 milligrams per cubic meter (mg/m3) from well VW-1 to <br /> 100,000 mg/m3 from well VW-4 <br /> CONCLUSIONS <br /> Utilizing the vacuum and distance measurements obtained during the VET, an effective <br /> radius of ini`luence can be estimated for the site The effective radius of influence is defined <br /> as the radial distance from a vapor-extraction well within which recorded vacuum levels <br /> indicate that subsurface air flow rates are sufficient for remediation RESNA estimates that <br /> a wellhead flowrate of 110 cfm and vacuum of 70 inches of water will result in an effective <br /> radius of influence of approximately 70 feet Alternatively, a wellhead flowrate of 30 cfm <br /> and vacuum of 25 inches of water will result in an effective radius of influence of <br /> approximately 25 feet The I C engine influent and effluent vapor samples collected from <br /> extraction wells VW-1 and VW-4 indicated a destruction efficiency for benzene and TPHg <br /> of greater than 94 percent <br /> Based upon the VET data, RESNA concludes that vapor extraction is a feasible method of <br /> remediating soil at this site Based on subsurface investigations performed by RESNA in <br /> June and December 1991, additional vapor-extraction wells will be required in the vicinity <br /> of the existing tanks to effect remediation of soil between the depths of 15 and 40 feet bsg <br /> The radius of influences and flow rates estimated above can be further evaluated and the <br /> number and location of additional vapor-extraction wells can be selected as additional <br /> subsurface environmental investigation is performed <br /> ARCO is planning to remove the existing tanks and install new tanks during the first quarter <br /> of 1992. The data from the tank replacement investigation will be used to assess whether <br /> additional soil borings and/or vapor-extraction wells are necessary This report summarizes <br /> data collected during the VET and presents interim conclusions regarding the feasibility and <br /> design characteristics for vapor extraction Submittal of this report to regulatory agencies <br /> is not required at this time, however, we recommend attaching this report to the interim soil <br /> remediation plan being submitted to the San Joaquin County Public Health Services, <br /> Environmental Health Division for public review We also recommend pertinent data <br /> regarding vapor extraction be submitted with an application for a permit to construct and <br /> operate a vapor-extraction system <br /> to0109ecar <br /> 30003-5 3 <br /> I <br />