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CaliforniSRegional Water Quality Cetrol Board <br /> Central Valley Region I z <br /> Katherine Hart,Chair1 <br /> Linda S. <br /> G.Brown,Jr. <br /> 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Governor <br /> Acting Secretary/or Phone(916)464-3291 • FAX(916)464-4645 <br /> Environmental http://www.waterboards.ca.gov/centralvalley <br /> Protection <br /> 2 May 2011 <br /> DESJC, M. Benson <br /> Defense Distribution Depot San Joaquin <br /> P.O. Box 960001 <br /> Stockton, CA 95296 <br /> DRAFT NORTHWESTERN CORNER GROUNDWATER OPERABLE UNIT REMEDIAL <br /> DESIGN/REMEDIAL ACTION WORK PLAN, 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 Northwestern Corner Groundwater Operable Unit Remedial Design/ <br /> Remedial Action Work Plan (Draft Work Plan), received 16 February 2011 . HDR I e M <br /> prepared the Draft Work Plan on behalf of Defense Logistics Agency Enterprise Support <br /> San Joaquin, California (DLA) for the Defense Distribution Depot San Joaquin Tracy site. <br /> The purpose of the Draft Work Plan is to present the design of the extraction well network and <br /> pump and treat system that is documented in the January 2011 Draft Record of Decision <br /> Remedy for the Northwestern Corner Groundwater Operable Unit. Central Valley Water Board <br /> staff's comments are presented below. <br /> COMMENTS <br /> 1. Central Valley Water Board staff agrees with the proposed locations for extraction wells. <br /> However, staff finds it difficult to evaluate DLA's rational for proposed extraction well <br /> locations and depths because the data are scattered on multiple maps and cross <br /> sections in the Draft Work Plan. For example, the proposed locations for three new <br /> extraction wells, shown on cross section Figure 5-2, are not shown on cross section <br /> location map Figure 2-4. Although the proposed locations are shown on map <br /> Figure 5-1, one must refer to Figure 2-4 for cross section reference. Another example of <br /> scattered data can be seen by reviewing cross section B-B', shown on Figure 2-6 and <br /> Figure 5-2. Figure 5-2 presents the vertical locations of the three proposed extraction <br /> wells. However, the lithologic soil boring data DLA used to place these wells are only <br /> shown of Figure 2-6. DLA should revise the figures to make the proposals clear to <br /> readers of the Draft/Final Work Plan. <br /> 2. It is extremely important to complete each new extraction well within permeable <br /> materials of the Upper and Middle Hydrologic Zones into which dieldrin-contaminated <br /> water was injected. However, the Draft Work Plan does not outline methods and <br /> procedures that field staff will implement to ensure that the extraction wells are screened <br /> within these.materials. The soil in the saturated zone must be sampled continuously <br /> during well installation to verify the presence of the expected permeable materials. In <br /> California Environmental Protection Agency <br /> ¢d Reevcled Paper' <br />