SITE INFORMATION AND CORRESPONDENCE

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Mr. Mike Desso • -2 - 3 November 2009 Nestle USA Inc. dependant on the flow modeling, but not confirmed by monitoring wells. Central Valley Water Board staff concluded that the two proposed wells in the Well Work Plan needed to be relocated to confirm that the side-gradient extent of the capture zone encompasses the entire width of the site as predicted by Nestle modeling. During the 22 October conference call, staff expressed concern that the locations proposed in the Well Work Plan were too close to the center of the predicted plume. Following the call, ECM addressed staff concerns in the 2 November 2009 addendum to the Well Work Plan that relocated the proposed wells. Industrial Avenue Site Treatment System The System Work Plan proposes to temporarily discontinue pumping of groundwater in one of the two extraction wells at the former NestlB facility. Currently, the extraction wells are both pumped at 30 gallons per minute (GPM) for a system total of 60 GPM. Pumping of EU-3 would be stopped and EU-4 would continue to be pumped at 30 GPM. The stated purpose is to determine if a zone of relatively stagnant or slow moving groundwater with elevated concentrations of trichloroethylene (TCE) exists between the extraction wells. Nestle has predicted the existence of this zone by modeling groundwater flow. Central Valley Water Board staff concludes that the proposal is not acceptable because it may reduce the onsite capture zone area by approximately 35 percent and increase the mass of TCE migrating offsite. Staff does not object to system modifications that would remove TCE within a stagnant zone provided that it is accomplished without reducing the capture zone area. Our estimate of capture zone area reduction is based on the System Work Plan model outputs presented as Figures 3 and 4; our concern regarding offsite TCE migration is highlighted by the recent arrival of TCE at monitoring well M-10A, located approximately 1,050 feet directly down-gradient of the Industrial Avenue site. The TCE concentration trend in M-1 OA between June 1988 and April 2009 is graphed on the attached figure. Stockton Avenue Site Monitoring Wells The Well Work Plan proposes the installation of two monitoring wells near the former sewer line leak at 519 South Stockton Avenue. The stated purpose of the wells is to evaluate the extent of influence of the groundwater extraction system in the C Zone, 143 to 158 feet beneath the surface. The current site conceptual model (SCM), prepared by AMEC in January 2009, concludes that concentrations of TCE and other constituents of concern within the C Zone at the Stockton Avenue site are the result of migration from the City sewage treatment ponds near the Stanislaus River, and not the result of a sanitary sewer leak in South Stockton Avenue. Therefore, Central Valley Water Board staff believes that the purpose of the proposed wells should be to verify this conclusion by comparing concentrations in the new wells with concentrations in B Zone wells near the sewer leak and with concentrations in C Zone wells that monitor the plume emanating from the sewage ponds. The SCM concludes that concentrations of TCE in the B Zone beneath 519 South Stockton Avenue are the result of a sewer line leak. Therefore, an investigation should be conducted on groundwater within the B Zone to confirm that concentrations of TCE and other constituents of concern resulting from the sewer line leak have been sufficiently reduced to justify shutdown of the treatment plant.