ARCHIVED REPORTS XR0006538 - Laserfiche WebLink

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The presence of methane (CH4) indicates that a number of the wells had progressed into methogenesis The levels of electron acceptors present and the presence of the reaction products, carbon dioxide, methane and ferrous iron indicate that the bacteria in the soil and the compounds in the groundwater have the capability to consume a significant amount of hydrocarbons The gasoline range hydrocarbon plume associated with this site is declining in concentration and should _untinue to do so, since the removal of the source in the softs beneath this site RISK BASE CORRECTIVE ACTION— RBCA TIER 2 In order to help determine the risks associated with this site a Risk Base Corrective Action (MBCA) Tier 2 Risk Assessment was performed, see Appendix G ' During the Tier 2 Assessment, Site-Specific Target Levels (SSTLs) were calculated, using the RBCA Spread Sheet System, for the following compounds of concern (COCs) • Benzene in groundwater and subsurface soils using the current EPA Cancer SF for Benzene • Toluene in groundwater and subsurface soils • Ethylbenzene in groundwater and subsurface soils • Xylenes in groundwater and subsurface soils • MTBE in groundwater and subsurface soils • TPHg as Hexane in groundwater and subsurface soils Two potential transport pathways were considered during the Tier Two investigation of this site Vapor Inhalation and Groundwater Ingestion The third mayor pathway, soil ingestion, was not considered because there is no documented contamination in the upper three feet of soil and the site is paved over limiting the probability of the ingestion of contaminated soil Vapor Inhalation was divided into two categories I Volatilization to onsite inside air, this was not considered for this study because the groundwater and soil plumes are not currently located beneath the station building and the modeling for inside air does not take this into account 2 Volatilization to onsite outside air 9 R603 Update 053/CLOSURE 2 10198