SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

h MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 255-3000 Sacramento, CA 95827-3098 Q CALNET: 8-494-3000 TO: Antonia K. J. Vorster FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 12 November 1992 SIGNATURE: ✓r� JCGG/A � SUBJECT: REVIEW OF DRAFT FINAL FEASIBILITY STUDY (FS) REPORT AND PROPOSED PLAN FOR OPERABLE UNIT NO. 1, DEFENSE DISTRIBUTION REGION WEST (DDRW), TRACY, SAN JOAQUIN COUNTY I have reviewed the Draft Final FS Report and Proposed Plan (PP) for Operable Unit No. 1 (OU-1) at DDRW, Tracy submitted on 13 October 1992. A response to our comments on the draft versions of the FS Report and the PP were provided. It appears that the Draft Final FS Report and PP were revised, sometimes substantially, to reflect many of the Board's concerns, but there are still some outstanding concerns which are discussed in separate sections below. However, based on the past cooperativeness and good-faith efforts of DDRW, Tracy, we approve the Draft Final FS Report and Proposed Plan. DRAFT FINAL FEASIBILITY STUDY REPORT 1 . In our review of the Draft FS Report, letter dated 7 August 1992, we requested that cost analyses be developed for different aquifer cleanup scenarios. The analysis presented in the Draft Final FS Report was unsatisfactory. Because DDRW, Tracy has retracted the originally proposed cleanup levels of 2.5 micrograms per liter (µg/1 ) for trichloroethylene (TCE) and 0.7 µg/l for tetrachloroethylene (PCE) , cleanup of the aquifer to levels greater than these concentrations may not comply with all of our applicable or relevant and appropriate requirements (ARARs) , particularly Resolution No. 92-49. Tracy has agreed to use the aquifer cleanup levels of 5.0 µg/1 for TCE and 0.5 µg/l for PCE because these levels of remediation have been established for DDRW, Sharpe. Sharpe proposed 0.5 µg/l as an aquifer cleanup level for PCE based on the assumption that when the overall cancer risk associated with cleanup of TCE is 5.0 Ag/l , other carcinogens are reduced to levels below detection limits. The concentration of 0.5 µg/l is neither the Secondary Maximum Contaminant Level (MCL) nor the 10-` cancer risk estimate for PCE. In addition, the 10_s cancer risk estimate for TCE is not 5.0 Ag/l , but is 3.0 Ag/l . The Project Managers at DDRW, Tracy and DDRW, Sharpe should meet and discuss the proposed aquifer cleanup levels. If the goal of DDRW is to have consistent aquifer cleanup levels at both sites, then the aquifer cleanup levels for the contaminants of concern should be based on valid water quality criteria and should not be represent a potentially unachievable cleanup objective for either site. 2. Table 2.2-6 presents the proposed cleanup levels and proposed treatment standards for each of the constituents of concern for OU-1 . It is apparent that there is still confusion between the aquifer cleanup level and the treatment