ARCHIVED REPORTS_RESPONSE TO COMMENTS ON DRAFT REMEDIAL ACTION PLAN 2015

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Page 5 5. As discussed at the 14 January 2015 monthly project conference call, Central Valley Water Board recommends implementing source removal in the core of the TCE plume originating at the City of Ripon wastewater ponds (southern TCE plume). The concentrations of TCE and its daughter products are highest in the vicinity of wells TH- 10 and M-31C1/C2/D and do not appear to be decreasing. Nestle must minimize the threat posed to nearby receptors by reducing the mass to levels that can be controlled by passive actions such as NINA. In 2015 groundwater extraction and treatment and/or in situ remediation must be implemented to reduce contaminant mass in this area. If Nestle chooses to implement groundwater extraction and treatment, the treated groundwater should be injected into the A Aquifer Zone, or alternatively, at a location/depth that helps reduce the potential for southward migration of the TCE plume in this area. Please submit a draft work plan to conduct these actions by 31 May 2015. Nestle Response: To clarify, COCs have not been detected in samples from M-31C2/D. Although the COC concentrations at TH-10 and M-31 C 1 have been relatively stable over the past decade, it does not mean concentrations won't decrease rapidly in the future. For example, the concentration of TCE and breakdown products remained stable for approximately 20 years at M-1701 before COC concentrations decreased by two orders of magnitude within five years to concentrations that are now lower than or close to the MCL. The 2011 Feasibility Study highlighted the fact that in situ remediation and groundwater extraction were not feasible remedies for impacted groundwater near the lagoons. There is no new information to suggest remediation is feasible in this area. In fact, the new information from the transducers indicates the hydraulic conditions are more complicated than those envisioned when the 2011 Feasibility Study was prepared. The Water Board staff has proposed pumping from the intermediate aquifer and re-injecting treated water into the upper aquifer. High rates of groundwater extraction and injection in this area could have the following negative side-effects: • High rates of groundwater extraction could further decrease water levels during a period of drought,promoting subsidence and potentially jeopardizing the integrity of the clay liner underneath the primary treatment ponds, causing larger groundwater quality problems, • Injection of treated groundwater into the Upper Aquifer would increase water levels and more mounding beneath the City of Ripon wastewater lagoons and percolation fields potentially interfering with the ability of the City of Ripon and Diamond Pet Food to infiltrate treated wastewater, • Increased mounding in the Upper Aquifer could enhance movement of shallow groundwater with higher salt content near the lagoons, extending the area of groundwater impacted by dissolved inorganic constituents, and • Increased mounding could also enhance groundwater velocities away from the lagoons, which can increase the likelihood of impacts to receptors. As discussed during our 12 February 2015 teleconference, more data is needed to assess appropriate remedial actions for the lagoon area. Nestle proposes to collect more data using a high resolution site characterization approach which will be described in the 30 April 2015 Work Plan for Additional Characterization and Well Installation. Nestle respectfully requests the approval from the Water Board to postpone the 31 May 2015 Work Plan submittal date until there is sufficient time to collect and analyze the new data and reassess the feasibility of remediation in this area.