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STA_7!ErJF CALIFORNIA- Environmental Protection Agency PETE WILSON Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD _ <br /> CENTRAL VALLEY REGION <br /> � = <br /> 3443 Routier Road, Suite � ^� L iiiFl_Ti1 <br /> Sacramento, CA 95827-3098 �=- <br /> PHONE: (916) 255-3000 ` a <br /> FAX: (916) 255-3015 4 OCT -5 PH 3: 06 0.�,....=s <br /> 3 October 1994 <br /> Mr. Darren Denning <br /> Shell Oil Company <br /> P. O. Box 4848 <br /> Anaheim, CA 92803 <br /> SOIL VAPOR EXTRACTION FEASIBILITY STUDY, SHELL OIL COMPANY, STOCKTON <br /> BULK FUEL TERMINAL, SAN JOAQUIN COUNTY <br /> I have reviewed Pacific Environmental Group, Inc.'s (Pacific) 29 August 1994 Soil Vapor <br /> Extraction Feasibility Study report for your Stockton terminal. The feasibility study (FS) was <br /> performed to determine if soil vapor extraction (SVE) is a viable technology to remediate soil and <br /> ground water contaminated with petroleum hydrocarbons at the terminal. My comments on the FS <br /> are presented below. <br /> 1. Monitoring wells (MWs) 2, 16, and 20 were used as extraction wells (EWs) during the test. <br /> The report gave depths to water for MWs 2 and 20 but not for MW 16. This should be <br /> included in the report. <br /> 2. The report stated that based on Pacific's experience at similar sites, the SVE radius of <br /> influence in the vadose zone at the site is likely to range from 20 to 40 feet. The report also <br /> stated that MW 13, which is about 21 feet away, was the observation well (OW) for MW 2; <br /> MW 16 had MWs 10, 11, and 17 for OWs, which were approximately 98, 77, and 90 feet, <br /> respectively, from MW 16; and MW 20 had MWs 21 and 22 for OWs, each approximately <br /> 17 feet from MW 20. <br /> Based on the SVE radius of influence of 20 to 40 feet obtained at similar sites, the use of <br /> OWs which were way beyond the radius of influence of MW 16 was inappropriate. In future <br /> tests, OWs should be placed where there is a good likelihood of influence by the extraction <br /> well. <br /> 3. The report stated that vacuum influence was not measured in any EW and the vadose zone <br /> permeability was estimated based on a radius of influence of 20 to 40 feet obtained from <br /> similar sites. The report also stated that the relatively low permeability of the vadose zone <br /> soils and the limited well screen above the saturated zone caused the absence of vacuum in the <br /> extraction wells. <br />