ARCHIVED REPORTS_RESPONSE TO COMMENTS ON DRAFT REMEDIAL ACTION PLAN 2015

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Nestle USl1 W Wes-to r5- SUZETTE -1 LI Good Food,Good Life Nestle has established a thorough monitoring program for the site. Since 2005, that program has routinely monitored the water quality of your well and several other private wells located south of the Stanislaus River. The 2014 Annual Report will include all this water quality data that will be submitted to the Water Board on March 31 with a copy to you. Nestle continues to track the movement of impacted groundwater and respond to the new information that the monitoring program provides in the area south of the City of Ripon lagoons. Analysis of the sample results from the wells installed during 2003 to 2006 confirms that the complex groundwater flow patterns in this area are influenced by dynamic hydraulic stresses on the aquifer system. The hydrology in this region is influenced by the water levels in the Stanislaus River, the City-owned wastewater treatment lagoons, the recharge ponds operated by Diamond Pet Food, and the wells pumping groundwater in the area. To get a more detailed understanding of the hydrology, Nestle collected pressure transducer data from 16 wells on both sides of the Stanislaus River over the course of more than three years. Nestle will present the results of this study in the upcoming 2014 Annual Report. Nestle's consultants are using the results of this study to update the groundwater flow model for the site. They are also working on a work plan for additional characterization on the southern portion of the plume for review and approval by the Water Board. You will receive a copy of that work plan as well. The updated groundwater flow model and new groundwater characterization data will be used to identify appropriate next steps for addressing COC concentrations south of the Stanislaus River. 2 -Natural Attenuation: The data generated from the Monitored Natural Attenuation (MINA)work summarized in Appendix B.4 of the 2011 Feasibility Study indicates that natural attenuation in the vicinity of the City of Ripon wastewater lagoons is occurring. That work provides strong evidence of the natural degradation of COCs, including vinyl chloride, but was of limited scope, since it essentially was a pilot test of MINA. Nestle submitted a MINA Work Plan to the Water Board March 27, 2014. The proposed study is on a larger scale and is proposed for a longer duration than previous work. The study will identify areas of the entire site where natural attenuation processes are promoting aquifer restoration at a rate comparable to one that can be practicably achieved using active remedies. The MINA Work Plan does not recommend foregoing active remediation in areas where natural attenuation processes may be deficient. Nestle recognizes that the COC concentrations at certain wells (wells TH-10 and M-31 C1) have been relatively stable over the past decade. However, we have seen evidence that even stable concentrations can improve rapidly. The concentration of COCl remained stable for approximately 20 years at a monitoring well located north of the City of Ripon treatment lagoons (well M-1701) before concentrations decreased from greater than 100 micrograms per liter(ug/L) to approximately 1 ug/L within five years. This trend is encouraging because it shows that concentrations can decrease rapidly as natural bacteria in the aquifer adapt and breakdown COCs over time. Natural attenuation of COCs certainly is occurring, and although