SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr.Russe 11 Chapin 1766 W.Monte Diablo Avenue Page 5 of 5 Even though the EHD did not believe that the site was ready for closure, the EHD did carefully evaluate all of the information provided to determine if site closure could be justified. At this time, the EHD has not been provided with the information and tools necessary to concur with the closure request. The persistent high contaminant concentrations in the four extraction wells are suggestive of soil washing or of a fairly large mass of contaminants related to the site that remains uncharacterized. As plume capture zones have limited down-gradient extent, it appears that most of the captured contaminants originate onsite and are being prevented from migrating toward the southwest. It has been claimed that continued remediation is not cost-effective, but there has been no demonstration of this claim. Without knowing the true remaining sorbed and dissolved masses, the contaminant flux rates, etc., it is not possible to calculate the efficiency of the current remediation effort, much less make a determination of cost-effectiveness. The primary concern of the EHD is fulfillment of our mission to protect public health and groundwater resources, as well as minimize potential liability of all parties should an incident occur that could be attributed to a decision making process that leads to closure of sites with large contaminant masses knowingly and intentionally left in place. The best way to prevent an adverse effect on public health under these circumstances is to be certain that the contaminated site is well understood, and the controls exerted on contaminant migration by the interaction of site hydrology and geology are thoroughly characterized and understood, and are properly managed. To achieve these goals, the EHD reviews the models by checking every statement and conclusion to be sure they are based on reliable data and are consistent with well-accepted scientific principals and practices. The accepted model should be well tested, and all potential alternative models should be shown to be unlikely based on site data. In summary, the EHD has repeatedly explained regulatory requirements to Mr. Chapin (Chapin Brothers, Inc.) since the UST's at the site were registered and the site contamination was documented. For various reasons, removal of the UST's and compliance with corrective action requirements has taken many years. It is the opinion of the EHD that further corrective action is required for this site as it is not well understood, public health is not well protected, and restoration of groundwater for future beneficial use has not been achieved, nor has an estimate of when it will be achieved been provided. If you have any questions regarding this matter please contact Margaret Lagorio, Supervising REHS at (209) 468-3449 or Nuel Henderson, RG, at (209) 468-3436. Sincerely, Donna Heran, REHS, Director Environmental Health Department c: Russell Chapin, Chapin Brothers Inc., 1203 Carlton Ave., Stockton, CA 95203 CVRWQCB—James Barton