SITE INFORMATION AND CORRESPONDENCE

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Off-Site Domestic Supply Wells -2- 22 November 1991 DDRW, Tracy I believe that it is premature for DDRW, Tracy to state that it is not the source of the carbon tetrachloride for the following reasons (as discussed in a telephone conversation with Mr. Marshall Cloud at DDRW, Tracy on 15 November 1991) . 1. The site-wide Remedial Investigation (RI) has not been completed. All of the waste management units (WMUs) have not been investigated in the southern end of the site. Therefore, there are no data to indicate whether or not wastes from these WMUs have impacted ground water. DDRW, Tracy's claim regarding it not being the source of carbon tetrachloride (or any other ground water contaminant) from that area cannot be verified until further sampling, as part of the site-wide RI, has been completed. 2. DDRW, Tracy has not developed an adequate historical water level data base. Because site-wide ground water level measurements have not been conducted at the site on a consistent basis, potential seasonal influences on flow direction have not been determined. In addition, due to a lack of monitor wells at the southern and southeastern portions of the site, potential easterly ground water flow components cannot be verified. If the previously reported ground water flow direction of northeasterly is correct, then the southern end of the site would be directly upgradient from the Rose and Robertson residences. WMUs in the southern end of the DDRW, Tracy site are potential sources of VOC ground water contamination. 3. DDRW, Tracy has not developed an adequate historical water quality data base. Many existing wells across the site have not been sample on a consistent basis and analyses for minerals have generally not been performed. This information is needed to fingerprint the water quality both on- and off-site. 4. The quarterly ground water monitoring program has been implemented only within the last year and therefore, has not yet collected four quarters of data. In addition, the ground water monitoring program has never included monitoring of off-site supply wells. 5. DDRW, Tracy has conducted only one off-site well survey in 1987. This survey may have been incomplete and may now be out of date. An off-site well survey is critical to determine what wells may be potentially impacted by a contaminant plume and to determine what wells could potentially affect the migration of the plume. Monthly monitoring of the domestic wells appears to be excessive. Monthly monitoring of the Rose and Robertson residences, and any other potentially affected drinking water wells, over an extended period, would be unnecessary if bottled water was supplied as an interim measure. This excessive monthly monitoring would triple the analytical costs incurred by DDRW, Tracy. DDRW, Tracy should instead supply the bottled water to the Robertson residence, as soon as possible. This would eliminate the need for monthly ground water monitoring of these residences. As previously recommended, quarterly monitoring of off-site supply wells should be implemented by DDRW, Tracy as soon as possible. Of critical importance to this issue is the fact that within several acres of the eastern end of the DDRW, Tracy, there are at least three other potential source areas, besides DDRW, Tracy, of volatile organic ground water contamination. These other potential source areas are listed below.