ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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Nestle USA, Inc.—Ripon, CA January 28, 2011 2011 Revised Feasibility Study 9.2.2.1 Effectiveness There is a general consensus that the barrier must be installed to terminate in a low permeability soil layer to prevent vertical migration of groundwater (and COCs) from within the contained area, to beneath and outside of the contained area. It is important to ensure that no conduit wells penetrating the low permeability soil layer exist in the vicinity of the containment area, which could prevent sufficient containment of CDCs. However, if surface recharge over the containment area is minimal, due to climatic factors or engineering controls, and the containment area is completely encapsulated by low permeability walls, horizontal groundwater flow can be diverted around the source area with minimal vertical movement of groundwater within the contained area. Therefore, impermeable barriers could be effective for controlling the migration of COCs in groundwater and therefore this technology is retained for further evaluation. 9.2.2.2 Implementability Physical containment of groundwater using impermeable barriers is generally limited to shallower depths (i.e. <100 feet bgs) and smaller areas than those under discussion in this Revised FS. Furthermore, access issues and utility conflicts can be serious obstacles to the implementation of this technology. For these reasons, an impermeable barrier is considered to be implementable if the containment area is confined to the Site, and to depths of less than 100 feet bgs, and if access issues (i.e. sufficient clearance between buildings, roadways, and other obstacles) and utility conflicts can be cleared. Because the area of higher TCE concentrations (i.e. above 1,000 µg/L) is confined to the northern portion of the 230 Industrial Avenue parcel, and to depths of less than 60 feet bgs, an impermeable barrier around this area would likely be implementable. 9.2.2.3 Relative Cost The relative cost of an impermeable barrier surrounding the area of higher TCE concentrations beneath 230 Industrial Avenue (approximately 1,000 linear feet) to an average depth of 70 feet bgs would be classified as medium (< $2,500,000). 9.2.2.4 Conclusion The installation of an impermeable barrier has been retained for further evaluation for the Upper Aquifer beneath the Site, but will not be considered further for the Intermediate and Lower Aquifers, or for other off-site areas due to the implementability limitations discussed in 9.2.2.2. 9.2.3 Permeable Reactive Barriers PRBs, also known as "treatment walls", are generally installed across the flow path of impacted groundwater, where COCs are removed by reaction with amendments contained within the PRB. PRBs, like impermeable barriers, can be designed to limit the mass discharge from a source zone. However, unlike impermeable barriers, PRBs can also be effective technologies far downgradient of the source zone to contain the leading edge of a dissolved COC plume, 28