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! Department of Toxic Substances Control <br /> Yo <br /> Edwin F. Lowry, Director <br /> 88Cal Center Drive <br /> Winston H. Hickox Sacramento, California 95826-3200 <br /> Agency Secretary Governor <br /> California Environmental SEP 2 6 2003 <br /> Protection Agency <br /> ENVIRONMENT HEALTH <br /> September 22, 2003 PERMIT/SERVICES <br /> Mr. Marshall Cloud <br /> Remedial Project Manager <br /> Defense Distribution Depot—Tracy Site <br /> Post Office Box 960001 <br /> Stockton, California 95296 <br /> COMMENTS ON DRAFT SOIL GAS CLOSURE/CONFIRMATION SAMPLING WORK <br /> PLAN FOR DEFENSE DISTRIBUTION DEPOT TRACY (DDJC-TRACY), TRACY, <br /> CALIFORNIA <br /> Dear Mr. Cloud: <br /> The Department of Toxic Substances Control (DISC) received the Draft work plan on <br /> July 3, 2003. Fieldwork for the work plan will commence at the end of September or <br /> beginning of October 2003 at the latest. The work plan describes the <br /> closure/confirmation soil gas sampling and analysis that will be performed to support the <br /> evaluation of the effectiveness of the current soil vapor extraction (SVE) and bioventing <br /> operations at DDJC-Tracy and whether it is appropriate to designate the sites for No <br /> Further Action (NFA). DTSC has the following comments: <br /> Comments: <br /> 1.) According to Tables 3-1 through 3-4 all closure/confirmation sampling will only <br /> occur at one discrete depth interval per each Geoprobe location. Originally, <br /> when the baseline samples were taken in 1998, samples were taken from three <br /> depth intervals for each location ranging from 5 feet or 6.5 feet, 10 feet and 14 <br /> feet. Taking the baseline samples at multiple depth intervals allowed one to <br /> better assess the distribution of the contaminants through the varying lithology. <br /> In addition, multiple sample depth intervals help determine the locations to focus <br /> the in-situ treatment and whether or not the contaminants migrated from a <br /> shallow depth to a deeper one. The confirmation sampling methodology should <br /> follow the same thought process. In order to truly determine whether or not the <br /> cleanup objectives have been met, DTSC recommends that in locations where <br /> baseline results showed contamination throughout the interval of 5 feet through <br /> 14 feet, confirmations samples should be taken at the proposed 6 foot interval as <br /> California Environmental Protection Agency <br /> 0 Printed on Recycled Paper <br />