SITE INFORMATION AND CORRESPONDENCE

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Department of Toxic Substances Control Alan C. Lloyd, Ph.D. 8800 Cal Center DriveNEC, arzenegger Agency Secretary Sacramento, California 95826-3200 I_r- �v � Governor Cal/EPA ENVIRONMENT HEALTH December 21, 2005 PERMIT/SERVICES Mr. Marshall Cloud Remedial Project Manager Defense Distribution Depot—Tracy Site Post .Office. Box 960001 Stockton, California 93727-0525 CONCURRENCE ON THE FINAL DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN, CALIFORNIA GROUND WATER MONITORING WELL INSTALLATION WORK PLAN, TRACY SITE, SAN JOAQUIN COUNTY, TRACY, CALIFORNIA Dear Mr. Cloud: The Department of Toxic Substances Control (DTSC) received the above-mentioned Work Plan on December 8, 2005. The objective of the ground water monitoring well installation Work Plan is to provide additional ground water monitoring data to help define the ground water capture for the A and B Zone extraction wells in the western portion of the Tracy Annex along Banta Road adjacent to the Rose residence. The monitoring wells will be constructed of two-inch diameter, schedule 40 PVC, with either a 0.010" or 0.020" slot screen depending on the lithology encountered. The four long-term monitoring (LM) wells, denoted as LM180A/LM181B, LM182B/LM183C, LM184A/LM185B, and LM186A/LM187B will be installed along the west side of Banta Road within the Tracy Annex property. Each nested well location will consist of one well in the Upper Hydrologic Zone and one well in the Middle Hydrologic Zone. The new wells will monitor ground water fluctuations and hydraulic gradients influenced by the A-zone Extraction Wells (EW) EW018A, EW019A, EW020A and nearby B-zone extraction wells EW024B and EW025B. DTSC has reviewed the Work Plan and concurs with the installation of the four nested monitoring wells in an effort to better define the hydraulic capture of nearby A and B zone extraction wells.