SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Russell Chapin 1766 W. Monte Diablo Avenue Page 7 of 7 only negligible concentrations. The EHD does not believe this will be the case as it would appear that considerably more than 2.6 pounds of contaminants are likely to be in the ground water and/or the flux rate for the saturated zone sorbed contaminants is exerting a profound impact on ground water. As the CR does not provide the means to evaluate the effectiveness of the current groundwater remediation system, the EHD cannot approve termination of its operation at this time. You are directed to keep the groundwater remediation system operating until the EHD or the CVRWQCB approves turning it off. Also, quarterly groundwater monitoring must continue on the currently approved schedule until directed otherwise by the EHD or the CVRWQCB. While the above comments may seem to be overly critical, it should be noted that the problems posed by this site for closure consideration are not trivial, and a numerical model, such as the one produced by ATC, is an appropriate approach toward justifying a closure consideration. EHD is not certain that enough current data exists to fully justify a site closure consideration, but does believe the MODFLOW and MT31D models can be greatly improved. With good models in hand, additional data needs can be evaluated. EHD notes that even with acceptable models that support either ceasing groundwater remediation or a site closure consideration, it is most likely that a period of additional monitoring will be necessary to validate the models. Questions or comments may be directed to Nuel Henderson at (209)468-3436. Donna Heran, REHS, Director Environmental Health Division L Nuel C. Henderson, Jr., RG Margand g orio, REHS Unit IV - Site Mitigation, LOP Supervisor, Unit IV, LOP C: James L.L. Barton— CVRWQCB David Hankins—ATC Honorable Victor Mow—San Joaquin County Board of Supervisors