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1 CaliforniRegional Water Quality Control Board <br /> Central Valley Region <br /> Katherine Hart, Chair a' <br /> 11020 Sun Center Drive,#200, Rancho Cordova,California 95670-6114 <br /> Linda S.Adams (916)464-3291 •FAX(916)464-4645 Edmund G.Brown Jr. <br /> Acting Secretary for http://w .waterboards.ca.gov/centralvalley Governor <br /> Environmental Protection <br /> 31 May 2011 <br /> DESJC, M. Benson <br /> Defense Distribution Depot San Joaquin <br /> P.O. Box 960001 <br /> Stockton, CA 95296 <br /> DRAFT FINAL 2011 EXPLANATION OF SIGNIFICANT DIFFERENCES TO THE 1998 SITE- <br /> WIDE COMPREHENSIVE REORD OF DECISION, DEFENSE DISTRIBUTION DEPOT <br /> SAN JOAQUIN TRACY SITE, SAN JOAQUIN COUNTY <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff has <br /> reviewed the draft final 2011 Explanation of Significant Differences to the 1998 Site-Wide <br /> Comprehensive Record of Decision (Draft Final ESD), received 25 April 2011. HDR I e2 <br /> prepared the Draft Final ESD on behalf of Defense Logistics Agency Enterprise Support <br /> San Joaquin, California (DLA) for the Defense Distribution Depot San Joaquin Tracy site. <br /> Central Valley Water Board staff note that the Draft Final ESD includes substantial revisions to <br /> the November 2010 Draft ESD. Our comments are presented below. <br /> COMMENTS <br /> 1. Section 2.2, Section 2.3, and Table 2.1 of the Draft Final ESD, establishes a soil gas <br /> cleanup metric for soil vapor extraction (SVE) removal of trichloroethene (TCE) or TCE <br /> and tetrachloroethene (PCE) to levels that DLA believes impacts to groundwater quality <br /> would be mitigated. DLA proposes that only 75 percent of confirmation soil gas <br /> samples be required to be below the cleanup standards established in the 1998 Site- <br /> Wide Comprehensive Record of Decision (ROD). Central Valley Water Board staff <br /> disagrees with the change. If a confirmation soil gas sample concentration is not below <br /> a cleanup standard established in the ROD and DLA no longer believes that SVE is <br /> effective, DLA can demonstrate that the remaining TCE or TCE and PCE can no longer <br /> cause leachate concentrations to exceed the aquifer cleanup standards and perform a <br /> technical and economic feasibility evaluation. <br /> 2. It is unclear what the intent is of statement number 4 in Section 2.2 of the Draft Final <br /> ESD. Central Valley Water Board staff suggests the following alternative: The <br /> 1998 ROD selected SVE remedy at the subject sites was designed for groundwater <br /> protection. However, SVE may not be suitable for vadose zone cleanup to a risk based <br /> level that is protective of human health from vapor migration to indoor air. <br /> 3. In Sections 3.4, 4.4, and 6.4 of the Draft Final ESD, DLA indicates that proposed land <br /> use controls (LUCs) require indoor air quality evaluations for any currently occupied <br /> California Environmental Protection Agency <br /> CdRecycled Paper <br />