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LLML Aft 6070„ Crave the ReprWfunam Facers GVsabarreo, Alsy=a„ was identified as the primary contaminant of concern (COC) in Eastern GSA Second water, comprising approximately 90% ofthe total VOCs detected. Othcf C(R;s in ground water included lemachlomethene (FEE), cis-12-dichlotomhene (1)( 4), 1,1-EKT, bmmodichlommefhane, and chloroform. The highest can entog ms; of VOC common nants in Eastern GSA ground water were detected in the vicinity ofthe debris burial trenches. The highest pro-remer lation concentrations Of total VOCs and ME detected in shallow ground water near the debris burial trench was 74 microgram per liter bped ) and 71 pall, respectively, in 1992. Priorto the start ofrcmed'ution, the plume of ME in ground water exceeding the 5 pa/L drinking water MCI, extended approximately 4,200 feet offsitc. The baseline human health risk assessment for the Eastern GSA estimated an excess carcinogenic risk of 5 x 10 ` for ingesting ground water f m a hypothetical water-supply well located at the site boundary near the debris burial menthes. The risk associated with potential use of contaminated ground water m two existing ol£siro water supply wells (CDfI and SRI) was - approximately 10 . Thew risks wereealculated assumingthat an remedial actions were taken and the VOCs in Est 68A ground water migrated to Mem wells. 'The baseline human health risk assessment indicated that them was no unacceptable risk or hamm associated with potential exposure m VOCs in suttece or subsurface soil in the EmWer GSA, and no contaminams of concern were identified in these media. 'Ilmm is m surfaze wafer Present in the Easkm GSA. DOE subsequently re-evaluated the ME in subsurface mil in the Eastern GSA using the revised WE toxicity value that EPA adopted in Sepmmwr201J . The TCE con v0latilizing from subsurface mil that was calculated for outdoor air in the EastemGSA concentration 0.02 micrograms per cubic meters (µ er ). This concentration is below both the residential and mdusmial exposure air concentrations considered to be protective at a 10"6ex cancer risk level and For men-cancer covers calculated using the September 2011 ME toxicity value. The residential exposure ah eunceulmtioas considered to be pmfective m a 10 excess cancer risk keel and for non-cancer effects for ME arc o.48 Jim' and 2. 1 pg/mr, respectively (May 2016 EPA RSLsk The industrial air concentrations considered to he protective at a IDc excess cancer risk level and for non-cancereffcns for TCE are 3 AgAa3 and 8.a Jahn', respectively (May 2016 EPA RSLxt). The maximum historical ME concentration in unsaturated sum uram, suiVrock in the Ensure, GSA (0.024 milligrams per kilogram fmglkgl) is also below both the residential and industrial Regional Soil Screening Levels (May 2016) that incoryorave the revised TCI; toxicity value the EPA residential Regional Soil Screening Levels (May 2016) fro ME Ito goei mg/kg (me cancer risk) and 4.1 mg/kg (nmmancer eticcork dot industrial Regional Soil Screening Levels (May 2016) for WE are 6.0 mgdcg (mcros cancer risk) and 19 mg&g (noncancer eovets)_ The SWRI risk assessment determined that V)Cs and metals in soil, including samples collected from Me debris burial lrenchvVarma, did not pose an urmecephble risk or haunt Inhuman Or ecuingical receptors, or fbrther threat to ground water. As a recall, VOCs and metals were not designated as conmunirmnus ofconenn in surface Or subsurface soil in the Eastern GSA. Therefore, capping of or other remedial measures for the debris burial benches were not deemed necessary by DOE, EPA, DTSC, and the RWQCB, and it was not included as alternative in the GSA Feasibility Study or as a component ofthe selected remedy in the GSA ROD.