ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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Nestle USA, Inc.—Ripon, CA January 28, 2011 2011 Revised Feasibility Study Municipal, agricultural, and industrial water production wells operated throughout the Study Area and influenced COC migration. Most of the municipal wells were west and north of the Site, with one to the southeast. The groundwater pumping that occurred at the Site would have contained dissolved CDCs from onsite releases to groundwater beneath the Site, at least until operations ceased in 1994. Additional groundwater pumping occurred at the NPC to the southeast of the Site. A Caltrans well extracted irrigation water to the east. Agricultural wells operated south of the River, which is south of the City of Ripon WWTP. Many of these wells were constructed with screens that spanned across multiple aquifers. Groundwater pumping from these wells may have greatly influenced groundwater flow directions and plume migration in all three aquifers. Some of this groundwater pumping likely drew COCs in groundwater northward from the lagoons at the WWTP. Other wells, particularly the NPC (formerly known as Simpson Paper Company) well S-2, and the former Fiscalini irrigation well may have caused eastward and southward COC migration from the WWTP wastewater lagoons'"" The Corcoran Clay is a competent regional aquitard and, where continuous, reduces the potential for downward migration of contaminants between aquifers. However, many of the municipal, industrial, and agricultural production wells were screened in multiple aquifers and are likely to have transmitted shallow COCs-impacted groundwater to the Lower Aquifer by acting as vertical conduits across the Corcoran Clay. Higher downward hydraulic gradients exist near the WWTP treatment lagoons; these lagoons likely contribute significant recharge to the aquifer system.X""' This higher gradient, in combination with nearby "vertical conduit" wells, may have driven COCs impacts deeper into the Intermediate and Lower Aquifers near the City of Ripon WWTP. Similarly and nearer to the Site, "vertical conduit" wells are the most likely explanation for COC impacts to the Intermediate and Lower Aquifers. Vertical gradients exist near the Site, but they are not as pronounced as those near the WWTP. 4.2 SCM Conclusions The following conclusions are based on the observations and findings of the updated SCM: 1. The hydrostratigraphy beneath the Site has been revised, with four depth intervals between the water table and base of the Upper Aquifer at approximately 115 feet bgs as follows: the B subzone (water table to approximately 40 feet bgs), the Upper A-zone (approximately 50 to 80 feet bgs), the Middle A-zone (approximately 80 to 95 feet bgs), the Lower A-zone (approximately 100 to 115 feet bgs). 2. Onsite releases were contained by onsite pumping for facility water supply. Therefore, COC impacts discovered in 1986 (MW-1, MW-6, S- 3, and domestic wells on Acacia Avenue) were not the result of COC migration from on-site releases, but related to other discharges, 9