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e CLEANUP AND ABATEMENT ORDER NO. R5-2006-0720 NESTLE USA,INC. RIPON,SAN JOAQUIN COUNTY residual soil vapor concentrations and potential off-gassing from the groundwater plume as part of an investigation of potential vapor intrusion into buildings overlying the TCE plume. Depending on the findings of this investigation, additional SVE work may be conducted or Regional Board staff may concur on NFA and the systems will be decommissioned. 20. In November 2001 and July 2005,the Discharger submitted work plans to conduct a pilot test on In Situ Reactive Zone("IRZ")technology. The Discharger proposed to inject a food-grade product such as com syrup or molasses into the Upper Aquifer zone to create a reactive zone that will biodegrade TCE and its daughter products. The preliminary field work was completed in 2005 and the first half of 2006 and included vertical profiling of the Industrial Avenue source area. The vertical profiling shows there are still residual concentrations of TCE as high as 7,800 µg/L in the shallow portion of the Upper Aquifer Zone. Regional Board staff is currently reviewing the results of that field work and concurrence on the proposed pilot test is anticipated in 2006. 21.Although the degree of TCE plume containment that can be provided by the Discharger's extraction wells has not yet been fully determined, it appears that municipal well MW-9 captures and treats a portion of the TCE plume east of the Facility. The Discharger and the City of Ripon have entered into a binding settlement agreement that ensures that MW-9 will continue to pump and treat groundwater in the Intermediate Zone. By entering into the settlement agreement, the City of Ripon agreed to limit pumping at municipal wells MW-4 and MW-7 to specified levels and,with certain exceptions, to operate MW-9 at a minimum pumping rate of 600 gpm. Groundwater modeling previously suggested that, left unconstrained, supply wells MW-4 and MW-7 would have adversely affected the Discharger's ability to contain the TCE plume in the Upper and Intermediate Aquifer zones if the City of Ripon had continued to pump them at historical rates. Municipal well MW-9 has recently shown increasing levels of nitrate, so the City of Ripon may eventually need to decrease or eliminate pumping at MW-9 to maintain the quality of drinking water supplied to City residents. Because high pumping rates must be maintained to provide adequate capture of the TCE plume east of the Facility, the Regional Board will require the Discharger to implement additional remedial actions if the City of Ripon needs to reduce or stop extracting groundwater from MW-9. 22.On 18 April 2005, the Discharger notified Regional Board staff that the TCE plume had been detected in two private supply wells screened in the Upper and Intermediate Aquifer zones on the south side of the Stanislaus River. Concentrations of TCE, cis-1,2-dichloroethene, and vinyl chloride have been detected at concentrations exceeding California Maximum Contaminant Levels (MCLS) in both private supply wells since the initial detection of the TCE plume. The Discharger installed wellhead treatment on these wells within one week and has since been monitoring these wells twice per month to ensure the wellhead treatment is operating properly. 23.On 25 April 2005, the Regional Board issued an Order, pursuant to California Water Code Section 13267, requiring the Discharger to provide an interim water replacement contingency plan, monitoring plan, and investigation work plan to delineate the full extent of the TCE plume on the south side of the Stanislaus River.The Discharger submitted the Final Water Replacement Contingency Plan for the south side of the Stanislaus River on 6 June 2005 and the Final Investigation Work Plan for the southern portion of the TCE plume on I 1 July 2005. 6