Laserfiche WebLink
Nestle USA, Inc.—Ripon, CA January 28, 2011 <br /> 2011 Revised Feasibility Study <br /> 5.3.1 Source Removal <br /> COC mass-discharge from a source area is needed to sustain a COC plume. <br /> Effective remediation of the source area reduces mass-discharge, thereby <br /> causing the COC plume to diminish over time. <br /> Impacted groundwater can also release COC vapors to indoor air spaces, <br /> although this is not the critical exposure route for the Site. Section 6 below <br /> provides further details. <br /> 5.3.2 Containment <br /> Containment refers to stopping the flow of groundwater and associated COCs <br /> using physical or hydraulic means. <br /> Water supply wells that are screened across multiple aquifers were the critical <br /> exposure route analyzed when assessing COC containment for impacted <br /> groundwater. The Applicable or Relevant and Appropriate Requirements <br /> (ARARs) for this Site specify the allowable concentrations according to the <br /> various criteria appearing in Section 7. <br /> 5.3.3 Plume Reduction <br /> As discussed previously, the RAO for groundwater is to reduce the extent of <br /> COC impacts to groundwater and restore the aquifer to background <br /> conditions. In order to compare the overall feasibility of the remedial alternatives <br /> evaluated, it is necessary to estimate the time to reach RAOs. Because there is <br /> no common concentration-based value specified for the RAO, a common COC <br /> concentration endpoint was selected in order to complete the numerical modeling <br /> that was necessary to compare estimated remediation timeframes for the <br /> alternatives evaluated in this Revised FS report. A remediation endpoint of 5 <br /> micrograms per liter (pg/L) TCE in groundwater was used for performing model- <br /> based simulations of the remedial alternatives. This value is used to be <br /> consistent with previous modeling results, so that the relative cleanup times for <br /> various alternatives can be evaluated against a common benchmark. The use of <br /> this concentration is not intended to imply a final proposed RAO for groundwater <br /> is 5 pg/L TCE. The RAOs will be based on future basin plan water quality <br /> objectives and RWQCB policy as described above. <br /> 6 Distribution of COCs in Groundwater <br /> 6.1 Historical VOC Release Areas <br /> 6.1.1 Former Nestl6 Site (230 Industrial Avenue) <br /> Sampling data indicates that elevated TCE concentrations at the Site are limited <br /> to the B- and Upper A-aquifer subzones. Downward migration of groundwater <br /> with high dissolved TCE concentrations has not occurred at the Site beyond <br /> these depths"". Depth-discrete groundwater sampling, conducted in 1999, <br /> documented high TCE concentrations (up to 6,000 µg/L) in samples from the <br /> 13 <br />