ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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Nestle USA, Inc.—Ripon, CA January 28, 2011 2011 Revised Feasibility Study reaction rates are less predictable, and long-term maintenance costs may include adding organic substrates"" 9.2.3.1 Effectiveness Treatment of COCs by ZVI is expected to be highly effective, at least for 10 years or more, based on current researchx". It is important to note that TCE treatment by ZVI also can reduce TDS and immobilize arsenic in groundwater. For these reasons, a PRB composed of ZVI can be expected to be highly effective if installed with the objective of source zone containment and/or dissolved plume containment. A PRB "biowall" composed of mulch may also be effective, however, there is less industry-wide experience with this approach. 9.2.3.2 Implementability In general, the implementability challenges associated with PRBs are very similar to those for impermeable barriers; however, there are more options for PRB configurations than there are for impermeable barriers. For example, a PRB can be designed as a series of closely-spaced large diameter permeable borings backfilled with ZVI or other reactive media. Most conventional PRB installations have been limited to depths of approximately 30 feet bgs across a single water- bearing zone, where deeper installations have generally involved methods of injecting ZVI, resulting in a great deal of uncertainty with respect to ZVI placement and treatment effectiveness. Recently, a PRB configuration was installed to depths of approximately 60 feet across multiple water bearing zones for treatment of PCE and TCEx`. Therefore, we consider a PRB to be implementable to depths of at least 60 feet bgs, if access issues and utility conflicts can be cleared. The area of higher TCE concentrations (i.e. above 1,000 fag/L) that is confined to the northern portion of the Site, to depths of less than 60 feet bgs could be treated with a PRB downgradient of this area and therefore the PRB technology has been retained for further consideration. A PRB would not be implementable for addressing the widespread dilute COC impacts to the lower portion of the Upper Aquifer and the Intermediate Aquifer because the area of impact is approximately 2 square miles, crossing multiple aquifers and utility corridors within an urban area. The PRB installation itself, even if possible, would take years and would be very disruptive to the City of Ripon compared to other alternatives. Even if such a PRB could be installed, the constant cycling of various municipal supply wells will cause large variations in groundwater flow direction and velocity. These variations would have to be known and accounted for over the entire design lifetime of the PRB. Negotiations would have to be undertaken with the City of Ripon to control groundwater pumping such as not to interfere with the function of the PRB. Since negotiations with the City of Ripon are already underway to limit the impact of pumping on COC movement and to mitigate future impacts to active supply wells, a PRB is not needed. 30