ARCHIVED REPORTS_2013 ANNUAL REPORT

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Nestl6 USA, Inc., Ripon, California March 26, 2014 2013 Annual Report 4.4). The objective of the site remedy is to address the areas of highest COC concentrations at the Site through containment and source removal, since an area of high COC concentrations in groundwater appears to be acting as a continual source of dilute CDCs in the vicinity of well M- 10A downgradient of the Site. Containing or reducing COC concentrations in this area would allow natural processes to progress toward restoring groundwater quality. The selected remedy includes pump and treat in the Upper Aquifer in the vicinity of the Site, including areas to the northwest (see Section 2.3.1), institutional controls to restrict new well installations (Section 4.3), and implementation of in situ treatment as necessary10. The selected remedy also includes intrinsic remediation (monitored natural attenuation) and relies primarily on this passive action to restore the groundwater, especially in the Intermediate and Lower aquifers. As part of the RAP, Nestl6 is preparing a MNA Work Plan to evaluate and document areas of the COC plume where natural attenuation of COCs is occurring, particularly in the Intermediate Aquifer. MNA will be implemented as part of the remedy where appropriate. 4 OTHER KEY ACTIVITIES IN 2013 4.1 HIGH-RESOLUTION WATER-LEVEL MONITORING STUDY In January 2012, ECM implemented a long-term, high-resolution water level monitoring study using pressure transducers in select wells located near the WWTP lagoons and the Stanislaus River to evaluate groundwater response (Upper and Intermediate aquifers) to changes in lagoon/pond recharge and river stage. ECM installed 16 transducers in select Nestl6 monitoring wells (M-17C1, M-23A, M-30C1, M-31 C1, M-32C, M-34A, M-34C, M-44A, and M-44C) and in shallow City-owned wells located near the lagoons (W-1, W-2, W-3, W-4, W-5, and W-9). A transducer also was installed in Diamond Pet Food well TH-10. The transducers are programed to record hydrostatic pressure and temperature data on an hourly basis. With the exception of well W-3, data were collected from all transducers through the end of 2013. To further understand groundwater response to the City's recharge pond, the transducer in well W-3 was reprogrammed and relocated to the recharge pond on October 28, 2013. On December 31, 2013, the data loggers in the other 15 transducers were reprogramed to free memory and restart data collection on January 1, 2014. Transducer data are downloaded on a quarterly basis for review and comparison with river stage. The water-level monitoring study is planned to continue through 2014. To better understand groundwater response to changes in recharge, transducers at select wells will be relocated to wells near the City's recharge pond. The results from the study will be summarized in a letter report after sufficient data are available to assess groundwater flow in the recharge pond area. High-resolution water level monitoring also is planned in the MW-3 area to further assess Intermediate Aquifer groundwater flow and plume dynamics. In November 2013, a new pressure transducer was installed in municipal well MW-3. In January 2014, transducers in wells in the WWTP lagoon area were relocated to select monitoring wells near MW-3. 16