SITE INFORMATION AND CORRESPONDENCE_1992

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• MEMORANDUMS CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Antonia K.J. VorsterFROM: Robert Yeadon Camilla Williams, ) Senior Engineer Region 5 Region 5 DATE: 16 April 1992 SIGNATURE: SUBJECT: VAPOR EXTRACTION PILOT STUDY REPORT, DEFENSE DISTRIBUTION REGION WEST (DDRW), SAN JOAQUIN COUNTY As you requested, I have reviewed the subject report received on 18 February 1992. I also reviewed the work plan for this project and several other pertinent documents. The subject report was prepared by Environmental Science and Engineering, Inc. (ESE) for the U.S. Army Toxic and Hazardous Materials Agency (USATHAMA) in support of the Remedial Investigation/Feasibility Study at the Sharpe site. The report describes the results of a soil vapor extraction (SVE) study and a double ring infiltrometer (DRI) test. VAPOR EXTRACTION PILOT STUDY The vapor extraction pilot study was conducted in accordance with the original work plan and the results of this study shows that SVE appeared to be fairly successful . Soil vapor extraction has worked well at other sites as a remedial measure, and I concur with the conclusions of the report that SVE technology may be an effective remedial measure considering the types of chemicals and soil types at this site. I have the following specific comments: 1. As our comments on the original work plan stated, the area to be remediated by SVE should be accurately mapped both horizontally and vertically using soil gas data prior to constructing the vapor extraction wells. The mass of contaminants in the soil column should also be estimated. This will increase the efficacy of the remedial effort since it will allow strategic placement of the extraction wells, accurate design of the screen length in each well , and appropriate sizing of the air extraction system. 2. We recommend the use of passive wells to allow air into the soil column during vapor extraction. Air flow lines can then be directed through zones of soil contamination rather than relying on air from the surface to pass through these zones of contamination. Use of passive wells also reduces zones of air stagnation between adjacent vapor extraction wells and reduces the amount of air coming from uncontaminated soils in vapor extraction wells located at the periphery of the site (in effect, the use of passive wells can reduce the amount of clean air being treated) .