SITE INFORMATION AND CORRESPONDENCE_1993-2003

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Mr. Maurice Benson May 1 , 2003 Page 4 the environment and if the RAOs used at the time of remedy selection are still valid. 9.) Page 7-6, section 7.1.2.1, last sentence; In the draft final/final versions of the five-year review please show the observed capture zones from EWCC3 in the water level contour maps and state the effects of the EWs hydraulic containment of the western TCE plume in the text portions of the report. 10.) Page 7-6, section 7.1.2.3, fourth sentence; Discuss in the report the reasons for 54% TCE plume capture in the CA A-zone for 3Q02 and even less capture in 4Q02 with 50%. 11.) Page 7-7, section 7.1.2.5, fourth sentence; See specific question #9. Summary: Overall, the optimization of the OU1 remedy will need to continue through the next five-year review period. DDJC and the regulatory team will need to keep improving the effectiveness and efficiency of the OU1 remedy so it will meet RAOs and help maintain the protectiveness of the remedy for human health and the environment. The effects of the offsite TCE plume west of DDJC-Sharpe needs to be modeled to determine if an exposure pathway exists for indoor air pollution for residents living in the residential development and for on-base workers/residents. There appears to be a large discrepancy, upwards of 19 years, between DDJC's target year for achieving the remedial action cleanup levels and the target year recently calculated by WES modelers. DDJC/DLA needs to take into account the recent modeling results from WES modelers demonstrating that with the current well configurations it will take upwards of 30 years from now before remedial action cleanup levels are achieved. Future ground water reports or any report discussing the OU1 remedy must state the "accepted" target year established by either DDJC or WES modelers for OU1 to meet the remedial action cleanup levels. In addition, with the recent notifications by the U.S. EPA Region IX to lower PRGs for hexavalent chromium, total chromium, and TCE could possibly lead to the lowering of Federal and California MCLs. The lower MCLs would then affect the existing RAOs and would call in to question the protectiveness of the chosen remedy potentially leading to further remedial actions being taken at DDJC-Sharpe. The regulatory agencies want DLA/DDJC to be aware of this, since there is a good likelihood that these amendments to the PRGs will take place within the next five-year review period.