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STATE OF CALIFORNIA-Environmental Protectisency • PETE WILSON Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 3443 Routier Road,Sufte A _ Sacramento,CA 95827-3098 - PHONE:(916)2553000 FAX:(916)255-3015 hp� � 31 March 1995 Mr. Jim Pinasco Department of Toxic Substances Control 10151 Croyden Way, Suite 3 Sacramento, CA 95827-2106 PRE-DESIGN DATA REPORT FOR OPERABLE UNIT 1, DEFENSE DISTRIBUTION REGION WEST(DDRW) TRACY, SAN JOAQUIN COUNTY We have reviewed the Pre-Design Data Report for Operable Unit 1 (PDDR) for DDRW, Tracy submitted 16 February 1995. Pursuant to the Final Operable Unit 1 Record of Decision (ROD), DDRW Tracy, is required to conduct studies to evaluate the technological and economic feasibility of cleaning up the OU-1 plume to background concentrations, or to levels greater than background, but at a minimum to assure protection of beneficial uses of waters of the state (i.e.,MCLs, for TCE and PCE). The remedial system must be designed to be capable of cleaning up the OU-1 ground water to these levels. The PDDR presents the results of three-dimensional ground water model development, calibration, and simulation applications used to conduct these studies. These results are further provided in support of the proposed 10 percent design concept for the (OU-1) remedial design and the supporting preliminary design analysis and rationale presented in the PDDR. We further understand that the PDDR was prepared to provide a conceptual design basis for the RD/RA Work Plan. Our main concerns with the PDDR are regarding the evaluation of potential remedial design alternatives and the discussion and presentation of the different elements used in the development of the ground water flow and contaminant transport models. As discussed during the recent Project Manager's (PM) meeting, held on 22 & 23 March 1995, these concerns must be addressed prior to our concurrence with a conceptual design. Additional information must be submitted to evaluate the adequacy of the ground water flow and contaminant transport models, and to determine an acceptable remedial design alterative. As further discussed during the PM meeting, revisions to the PDDR may be submitted as an addendum or technical memorandums may be provided. We look forward to meeting with DDRW Tracy to discuss the model development process, modeling results, and the evaluation of the technological and economic feasibility of cleanup, in an effort to expeditiously move toward an acceptable remedial design concept. GENERAL COMMENTS The PDDR does not contain sufficient detailed information to demonstrate adequacy of the ground