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. MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 T0: Antonia K. J. Vorster FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 10 September 1991 SIGNATURE: (riAil7LL�cfJVI , SUBJECT: DRAFT SOLID WASTE MANAGEMENT UNIT ENGINEERING REPORT, DEFENSE DISTRIBUTION REGION WEST (DDRW), TRACY, SAN JOAQUIN COUNTY I have reviewed the Draft Solid Waste Management Unit Engineering Report for DDRW, Tracy. The Report was submitted on 10 June 1991 and was prepared by Woodward-Clyde (WWC) for the Corps of Engineers. The Report summarized past waste disposal practices and investigations and presented recommendations for further investigations of each waste management unit (WMU) . The Report was very well prepared and the format enabled a easy review and quick referencing. The summary tables were exceptional and were very useful in my review. GENERAL COMMENTS 1. The Report indicates that two of the WMUs may be regulated by the Toxic Pits Cleanup Act (TPCA) : WMU 3 (Industrial Lagoons) and WMU 6 (Building 28 Sump) . The criteria for regulation by the TPCA is that liquid hazardous wastes had to have been disposed in a WMU on or after 1 January 1985. If the WMU was constructed such that it had structural integrity and could therefore be considered as a tank, the WMU would not be regulated by the TPCA. 2. The Report indicates that in many of the WMUs the soils borings will be converted to monitor wells. However, rather than converting the borings to wells, DDRW, Tracy should consider using the analytical results of the soil samples to determine whether a monitor well is needed. If the analytical results of the soil samples indicate that the soils are not contaminated or that the contamination to be left in-place does not pose a threat to water quality, then a ground water investigation would not be necessary at the WMU. The soils and ground water investigations of the WMUs should be conducted it a phased approach. 3. In general , I agree with most of the recommendations for the remaining soils and ground water investigation of the WMUs. However, I am concerned that some of the recommendations are not sufficiently focused to the past waste disposal practices at a particular WMU. I also have a few comments on the recommendations that may optimize the data collection effort. These comments are not discussed by WMU, but are discussed below on the basis of the type of wastes, the sampling protocol and the method of analyses. a. In the WMUs in which soil samples are to be analyzed for inorganic constituents, the leachate of the soil samples should be analyzed for total dissolved solids (TDS) , electrical conductivity (EC) and pH. The analytical results of these parameters are useful indicators of whether the residual waste constituents in the soils may pose a threat to water quality by inorganic constituents. Analytical results for these constituents may ultimately be required if the contaminated soils are to be disposed in a landfill .