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JAMES GIOTTONINI <br /> PAGE 2 <br /> Considerations for Passive Alternatives <br /> The source is still present and active at this site. Although the tank system has been removed, <br /> a substantial mass of hydrocarbon impacted soil still remains. This mass of hydrocarbon <br /> impacted soil will act as a continuing source to the groundwater contaminant plume over time. <br /> Because of the uncertainty of the fate of this plume over time given the volume of the source <br /> material still remaining and unknown potential groundwater usage requirements, groundwater <br /> monitoring alone will likely not provide sufficient data to support a protective, reducing plume <br /> determination in a reasonable time frame. The cost of monitoring the site for some time, <br /> probably a number of years, is a critical factor that must be considered. <br /> There is a known downward flow factor in the groundwater system underlying the site. The <br /> impact of this downward flow factor on the ultimate fate on the existing contaminant plume is <br /> completely unknown at this time. The cost of installing and regularly monitoring and sampling <br /> additional monitoring wells in the deeper zones underlying the site to better understand this <br /> factor is a critical factor that must be considered. <br /> Considerations for Active Source Removal <br /> The vapor extraction wells in and around the source area are already installed and ready for <br /> utilization. There is a certain cost associated with the design and installation of a vapor <br /> extraction system at the site and this factor must be considered. <br /> Once the source area has been reduced, a shorter period of monitoring at the site will likely <br /> provide sufficient data to demonstrate a degrading, protective plume. The cost of a shorter <br /> period of monitoring after source removal is a factor that must be considered. <br /> Should sufficient source removal take place promptly, the need for deeper wells at the site <br /> would be re-evaivated and would depend primarily on the effectiveness of the reduction at the <br /> source area. The potential cost savings of not having to install, monitor and sample these <br /> wells on a regular basis must be considered. <br /> Taking into consideration the site specific factors, the current and potential uses of our groundwater <br /> basin, and the required cost effectiveness evaluation, please assess the course of action to be taken <br /> for this site and provide PHS-EHD with an update in the next quarterly report. If you have any <br /> questions or wish to discuss this letter in more detail, please contact Linda Turkatte, Senior RENS, at <br /> (209) 488-3441. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> Linda A. Turkatte, Senior REHS Margar t Lagorio, REHS <br /> Site Mitigation Unit Lead Senior <br /> c: CVRWQCB, Beth Thayer <br /> c: Jim Escobar, COS Public Works <br /> c: Tom Lutterman, Smith Environmental <br />