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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 TO: Antonia K. J. Vorster74A"///,/ FROM: Camilla Williams Senior WRC Engineer / Engineering Geologist DATE: 26 August 1991 SIGNATURE: 7> lfJ yjf�/G� YLt� SUBJECT: REVIEW OF 11 JULY 1991 PROPOSED PLAN, DEFENSE DISTRIBUTION REGION WEST (DDRW), TRACY, SAN 1OAQUIN COUNTY I have reviewed the 11 July 1991 Proposed Plan for the completion of the Remedial Investigation/Feasibility Study (RI/FS) for Operable Unit (OU) 1, submitted by the Corps of Engineers, for DDRW, Tracy. I have previously reviewed the RI Report for OU 1 and found it acceptable. Because Tracy plans to conduct a site-wide RI which can easily incorporate any deficiencies in the current investigation, we should approve the RI for OU 1 . However, the Environmental Protection Agency (EPA) and the Department of Toxic Substances Control (DTSC) have indicated that the RI/FS is incomplete because the Risk Assessment did not follow the EPA's Risk Assessment Guidelines (RAGS) . On 31 July 1991, the Proposed Plan was discussed in a telephone conference call between the EPA, the DTSC, the Regional Board, the Corps of Engineers, and Tracy. At that time, I provided my comments on the Proposed Plan. Most of my comments on the Proposed Plan are based on the analytical methods and sampling frequency of the monitor wells listed in Table 4 of the Proposed Plan. Tracy proposed sampling all of the on- and off-site ground water monitor wells to develop the data needed to perform a Risk Assessment in accordance with the EPA's RAGS. Listed below are my specific comments on the Proposed Plan, as discussed in the conference call . 1 . It is unnecessary to analyze the samples from all of the monitor wells for all of the analytical methods listed in Table 4 because some of the monitor wells are being sampled and analyzed for the same methods under Waste Discharge Requirements (WDRs) Order No. 90-275. Therefore, to collect this information a second time would be redundant. Tracy should use the information being developed as required by the monitoring program in the Order. The following wells are being monitored in accordance with the WDRs. Group of Type of Contaminant or Monitor Wells (Method of Analysis) Freouency MW-1 to MW-5, Volatile Organics (Methods 601 and 602) Quarterly LM-15, LM-28, Temperature, pH, and Electrical Conductivity LM-30, LM-49, Volatile Organics (Method 8240), LM-50, LM-53, Total Petroleum Hydrocarbons (Method 418.1) , LM-62 Polychlorinated Biphenyls and Pesticides (Method 8080) , Metals including Arsenic, Selenium and Mercury (Methods 6010, 7060, 7740 and 7471) MW-6 to MW-10 Volatile Organics (Methods 601 and 602) , LM-4, LM-27A, Temperature, pH, and Electrical Conductivity Every 2 Months LM-71, LM-79 Group of Type of Contaminant or