ARCHIVED REPORTS_STOCKTON AVENUE SYSTEM WELL E-2 POST-SHUTDOWN EVALUATION

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J ZVI.. NMENTAL COST MANAGEMENT,INC. Managing Cost and Liabflley 3525 Hyland Avenue,Suite 200 Costa Mesa,California 92626 Main;1714)662-2750 Fox,(714)662-2753 November 21, 2012 James R. Brownell, P.G. Central Valley Regional Water Quality Control Board 11020 Sun Center Drive, #200 Rancho Cordova, CA 95670 Re: Stockton Avenue System Well E-2 Post-Shutdown Evaluation Former Nestle USA, Inc. Facility Ripon, CA 95366 Dear Mr. Brownell: On behalf of Nestle USA, Inc. (Nestle), Environmental Cost Management, Inc. (ECM) submits this evaluation for extraction well E-2 following the shutdown of the Stockton Avenue Groundwater Extraction System (Stockton Avenue System) in October 2010. In a letter dated September 3, 2010, the California Central Valley Regional Water Quality Control Board (RWQCB) approved the shutdown of the Stockton Avenue System B-Zone extraction well E-2. As a stipulation of the shutdown approval, the RWQCB required post-shutdown monitoring to evaluate rebound trends. To complete this evaluation, the RWQCB established a monitoring frequency for wells E-2, M-8A, M-813, and M-52B (Figure 1) on a monthly basis for the first quarter, and then quarterly during the second, third, and fourth quarters. Nestle also completed three additional rounds of quarterly monitoring (for a total of six quarters) to provide additional data for the evaluation. Based on the evaluation of data collected between November 2010 and July 2012, ECM concluded that extraction well E-2 has remediated the residual TCE-impacted groundwater that was likely caused by the sewer leak in the vicinity of the Stockton Avenue site. The vadose zone impacts were previously addressed by soil vapor extraction in this area. The following sections present some details of the evaluation. Trichloroethene (TCE) and its breakdown products, particularly cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride, are the primary contaminants of concern (CDCs)for this evaluation. Rebound Evaluation ECM used the monthly and quarterly data (Table 1) collected for wells E-2, M-8A, M-8B, and M- 52B to evaluate if extraction well E-2 remediated the TCE release associated with the sewer line leak in the vicinity of Nestle's Stockton Avenue site. In addition, ECM used the data from well M- 53B during this evaluation because this well is a shallow A Zone well and is located approximately 150 feet northwest (downgradient) of E-2 (Figure 1). The evaluation presented below presents a discussion of each well and its associated TCE concentration trends post-E-2 shutdown, with the exception of well M-8A, which is an A Zone well (screened from 91 to 112 feet below ground surface) and has been non-detect for TCE since 1987. The breakdown products of TCE were not detected in any well during the post-shutdown evaluation period with the exception of one detection of cis-1,2-DCE in well M-53B in January 2011. Page 1 of 3