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1 _ <br /> a <br /> F February 10, 1992 - -- Working o Restore Nature <br /> P+ <br /> ARCO Station No. 2130, Stockton. California g t <br /> The results of laboratory anaivses of the vapor samples indicated that the influent TPHg <br /> concentrations ranged from 43.000 milligrams per cubic meter(mg/m)from well VW-1 to <br /> 100,000 mg/m' from well VW-4. <br /> CONCLUSION <br /> Utilizing the vacuum and distance measurements obtained during the VET, an effective <br /> radius of influence 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 iniluence of approximately 70 feet. Alternativeiv, a wellhead flowrate of 30 cfm <br /> and vacuum of 25 inches of water will result in an effective radit;s 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 efficiencv for benzene and TPHg <br /> of greater than 94 percent. <br /> i <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 /> J 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 /> u <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 inent data <br /> regarding vapor extraction be submitted with an application for a permit -onstruct and <br /> operate a vaporextraction system. <br /> Ott19=r <br /> 3oao3-s 3 <br /> j <br />