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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 NNN TO: Antonia K. J. Vorster FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 11 September 1992 SIGNATURE: SUBJECT: REVIEW OF THE DRAFT ENGINEERING REPORT FOR THE NELL MONITORING PROGRAM, DEFENSE DISTRIBUTION REGION WEST (DORM), TRACY, SAN JOAQUIN COUNTY I have reviewed the Draft Engineering Report for the Well Monitoring Program at DDRW, Tracy. The Draft Report was submitted on 13 July 1992 and was prepared by Woodward-Clyde Consultants for the Corps of Engineers. The Report summarizes the results of the first four quarters of ground water monitoring data: May 1991, August 1991, November 1991 and February 1992. The Draft Report also provides recommendations for on-going ground water monitoring. Overall , the Draft Report for the Well Monitoring Program is comprehensive and well prepared. In general , Woodward-Clyde continues to do a superior job of summarizing data in tables and on maps. These graphic presentations of data have been very useful in reviewing the report and interpreting the data. This Draft Report contained the major elements that are usually required in an annual report, including plume maps, summary tables and recommendations for on-going monitoring. My concerns with the Report have been divided into two types: Major Concerns and Specific Comments. My Major Concerns are those that must be addressed and incorporated into the site-wide Remedial Investigation/Feasibility Study (RI/FS) process. My Specific Comments must also be addressed but may not require significant changes in the Final Engineering Report for the Well Monitoring Program. MAJOR CONCERNS Wells Screened Above the Upper Horizon. The Draft Report, as in the previous quarterly ground water monitoring reports, does not include inthe evaluation of the upper horizon, the data collected from seven wells which are screened above the upper horizon (LM-4, LM-5, LM-27A, LM-30, LM-32, LM-43 and LM-58) . To accurately evaluate the upper horizon, water level and contaminant concentration (plume) maps must be developed using data from both the wells screened above and in the upper horizon. Without using the information from both sets of wells, significant errors are being made in the interpretation of the extent of the contamination. These errors may result in inappropriate remedial actions for both soil and ground water. It is unclear why data from wells screened above the upper horizon have not been included in the water level contour or plume maps of the upper horizon. It appears that the exclusion of these wells may be based strictly on lithology rather than considering the hydraulic aspects of the ground water system. Hydraulically, there appears to be little head difference (frequently, less than 0.1 foot) in the ground water elevation between the wells screened above and in the upper horizon. The table below compares the February 1992 ground water elevations for wells screened above and in the upper horizon.