SITE INFORMATION AND CORRESPONDENCE

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Well Monitoring Program -7- 11 September 1992 DDRW, Tracy 8. San Joaquin County Public Health Services wrote DDRW, Tracy, by letter dated 24 August 1992, expressing concern that a well survey had not been conducted. In response to the County's letter, Tracy should update the County by submitting the results of the off-site well survey that were included in this Draft Report (Section 5.0) . This survey was conducted in Spring 1992. 9. The results of the off-site well survey confirmed the presence of carbon tetrachloride above the Primary MCL in the Robertson (Well No. 1) and Rose (Well No. 2) domestic supply wells and confirmed the presence of TCE slightly above the Primary MCL (6.2 14g/1 ) in the Rose well . The well sampling also revealed that the Pombo well (26432 South Banta Road) (Well No. 11) had very low concentrations (0.652 µg/1 ) of chloroform. It should be noted that this off-site well is close to the All Pure Chemical site which is a confirmed off- site source of chloroform ground water contamination. 10. Section 6.06 of the Draft Report indicates that 1, 1-dichloroethylene (1,1-DCE) was detected in concentrations (11.9 to 13.6 µg/1 ) exceeding the California Primary MCL of 6 149/1 in samples collected from LM-32. This monitor well is screened above the upper horizon. Because 1,1-DCE was confirmed as a ground water contaminant, this constituent may need to have a cleanup level established as part of the Record of Decision (ROD) for OU-1 . 11 . Several metals were determined to have elevated concentrations above the MCLs in more than one quarter of sampling. These metals are: barium, cadmium, chromium, iron, manganese, mercury and nickel . Two of the metals, iron and manganese, occurred in concentrations that exceeded the Secondary MCLs. On- going monitoring for metals conducted prior to the completion of the site-wide RI, should be limited to these specific metals. Monitoring for other metals would appear to be unnecessary as their presence could not be confirmed nor even detected. 12. The recommendations for on-going monitoring did not appear to propose the submittal of an annual report. An annual report, which summarizes the previous four quarters of ground water monitoring data, appears to be the best format to discuss plume migration, make recommendations for on-going monitoring and to track the progress of a ground water remedial action. The Final Report for the Well Monitoring Program should specify that annual ground water monitoring reports will continue to be submitted for agency review. 13. The volume of the quarterly ground water monitoring reports should be reduced in the future. However, the content of the annual reports, should remain similar to this Draft Report. The quarterly reports should contain at a minimum, plume maps, summary tables of ground water levels and contaminant concentrations and brief discussions on the findings from that quarter. These discussions should include topics such as general trends in flow direction, significant changes in contaminant concentrations, anomalous points and difficulties associated with the collection, reporting and preparation of the quarterly report. The quarterly ground water monitoring reports may be reduced in volume by eliminating the submittal of the raw laboratory data sheets and general discussions on site conditions that have not changed with time. CKW:cw