SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Russell Chapin 1766 W.Monte Diablo Avenue Page 5 of 7 soil. Data, with a careful explanation and demonstration of its applicability, the model components and input values, should be provided to the EHD for further evaluation. Point 9: ATC discussed Criterion 4, contending that the EHD has exceeded the intent of the criterion by virtue of the low water quality and the lack of municipal water wells existing or planned for the area. The EHD notes that Criterion 4 is part of the Appendix A recommendations that are to be used with good professional judgment in light of all the site- specific factors. Water supply wells, if in the immediate vicinity, would certainly represent a receptor of very high vulnerability, but are not the only potential receptors of concern. A Compilation of Water Quality Goals, prepared by the Regional Water Quality Control Board, Central Valley Region, states that: In 1988, the State Water Board adopted Resolution No. 88-63, the Sources of Drinking Water policy. This policy specifies that, except under specifically defined circumstances, all surface water and groundwater of the state are to be protected as existing or potential sources of municipal and domestic supply, unless this beneficial use is explicitly de-designated in a Water Quality Control Plan. Groundwater in the area of the site has not been explicitly de-designated from beneficial use classification. As the current model does not convincingly demonstrate that the plume of impacted groundwater will not rebound and expand upon a return to natural conditions, the EHD must consider the possibility that the plume will expand and impact additional volumes of beneficial use groundwater in violation of the anti-degradation policy of the state. Point 10: ATC quotes Criterion 5 of Appendix A of the Tri-Regional Recommendations for closure consideration, which states: Pollutants remaining in groundwater do not create or threaten to create risk to human health and safety, or to future beneficial use(s) of groundwater. Patterns of existing and future demands for usable water resources in the area must be considered in determining what period of time is reasonable to reach non- detectable (or background) concentrations. ATC noted the opinion of the EHD that the models do not appear to be adequate to evaluate the threat to future beneficial uses of groundwater, and that a health risk assessment was not performed. Addressing neither of these two points, ATC cites Mr. Eric Mar, of California Water Service, who does not anticipate any future use of the area groundwater due to poor water quality believed to have resulted from inorganic pollutants from the Stockton Deep Channel. The view of the EHD on the water quality and beneficial use issues are discussed above and will not be repeated here. A health risk assessment for the contaminants to be left in place, in an area that includes residential use, has not been submitted and, therefore, cannot be evaluated. Groundwater has been as shallow as 10 feet bsg; so a property owner putting in a swimming pool could encounter impacted groundwater, which may represent a risk to human health. The EHD notes that even for areas of poor water quality, the return of impacted groundwater to background conditions within a "reasonable time period" must be considered under Criterion 5. If Mr. Mar had indicated a reasonable tine period, for instance 20 years, for which there were no