Laserfiche WebLink
MEMORANDUM • <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 361-5600 <br /> Sacramento, CA 95827-3098 ^^ ATSS Phone: 8-495-5600 <br /> TO: Antonia K. J. Vorster N FROM: Camilla Williams <br /> Senior WRC Engineer Engineering Geologist <br /> DATE: 24 July 1991 SIGNATURE: <br /> SUBJECT: REVIEW OF VAPOR EXTRACTION PILOT STUDY WORK PLAN, DEFENSE DISTRIBUTION REGION <br /> WEST (DORN), SHARPE SITE, SAN JOAQUIN COUNTY <br /> I have reviewed the Vapor Extraction Pilot Study Work Plan for the DDRW, Sharpe Site. <br /> The Work Plan was submitted by the U. S. Army Toxic and Hazardous Materials Agency <br /> (USATHAMA) on 28 June 1991 and was prepared by Environmental Science and Engineering, <br /> Inc. (ESE) . The Work Plan included proposals for the vapor extraction system and for <br /> double ring infiltrometer tests. On 19 July 1991 , I discussed my major comments and <br /> recommendations on the Work Plan with Mr. Craig MacPhee of USATHAMA and an approval <br /> form for the installation of seven vapor monitor wells, eight vapor extraction wells <br /> and four excavations was faxed to the Public Health Services of San Joaquin County. <br /> VAPOR EXTRACTION PILOT TEST <br /> In general , the Work Plan for the vapor extraction pilot system was fairly well <br /> presented and included schematics for the locations of the wells for the pilot test and <br /> construction diagrams for the vapor extraction and monitor wells. My major concern is <br /> that the rationale for the placement and design of vapor extraction and monitor wells <br /> was generally not discussed. My other comments and concerns are discussed below. <br /> I briefly discussed the plan with the staff of the Under Ground Tank Section to solicit <br /> their expertise on vapor extraction systems. Because this is a pilot system, I did not <br /> press my technical concerns with Mr. MacPhee but elected to let the vapor extraction <br /> system be installed as proposed, with the understanding that my recommendations were <br /> made for the purpose of optimization of the system, but that these concerns must be <br /> considered if and when future tests are planned prior to a full scale vapor extraction <br /> system. <br /> 1 . A map depicting each of the contaminated soil areas to be remediated (Soil Areas <br /> 8 and 14) in relation to the soils gas results and monitor wells in each area would <br /> have been beneficial . <br /> 2. It was unclear whether Soil Areas 8 and 14 were selected because these were the <br /> areas of the highest volatile organic constituent (VOC) concentrations from the <br /> soils gas surveys of the entire site. <br /> 3. It is unclear why distances between the vapor extraction wells (30 feet apart in <br /> Soil Area 8 and 15 feet apart in Soil Area 14) were selected. Commonly, vapor <br /> extraction wells are placed in a grid pattern, such as on 50 foot centers, across <br /> the entire soil contaminated area. However, for the purposes of a pilot test, <br /> coverage of the entire area would not be reasonable. <br /> 4. It is unclear why the vapor extraction wells had variable screen lengths and were <br /> placed at variable depths in the unsaturated zone. It is recommended that the <br /> screen lengths be the same for the purposes of a pilot test so that the results <br />