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Stantec August 15, 2013 Page 6 of 8 2. Petroleum Vapor Intrusion to Indoor Air . Petroleum release sites shall satisfy the media-specific criteria for petroleum vapor intrusion to indoor air and be considered low-threat for the vapor-intrusion-to-indoor-air pathway if(a) Site-specific conditions at the release site satisfy all of the characteristics and criteria of scenarios 1 through 3 as applicable, or all the characteristics and criteria of scenario 4 as applicable... The site meets the characteristics of Scenario 3. Specifically: • Benzene concentrations are less than 100 pg/L. Benzene concentrations in groundwater have been below 100 pg/L since the third quarter 2005; in addition, benzene has not been detected above laboratory reporting limits during the last two quarterly monitoring events. • The bioattenuation zone provides a separation of at least five vertical feet between the dissolved phase benzene and the foundation of existing or potential buildings: Depth. to water generally ranges from five to 11 feet bgs, with the exception of the first quarter 2006, in which the depth to water in two monitoring p q p 9 wells (MW-5 and MW-3)was less than five feet bgs. • Total TPH is likely less than 100 mg/kg throughout the entire depth of the attenuation zone. None of the soil samples collected from five feet bgs contained. TPHg at concentrations above laboratory reporting limits. Soil samples were not collected at five feet bgs from soil sample locations MW-3, MW-8, and GP-15, which contained TPHg concentrations greater than 100 mg/kg at depths of 10 to 20 feet bgs. However, based on sample results from other locations (GP-14 and GP-17), it.appears that the highest TPHg concentrations are present between 10 and 20 feet bgs, which corresponds to the initial release point of the bottom of the original UST excavation. TPHg concentrations in soil at five feet bgs at sample locations MW-3, MW-8, and GP-15 are likely less than the concentrations encountered at 10 to 20 feet bgs. These sample locations are also at least 40 feet away, from the current building foundation and the western property boundary. TPHg concentrations in soils from sample locations closest to the onsite and offsite buildings (MW-1, MW-5, and MW-7) were less than laboratory reporting limits. In addition, more recent soil samples collected during the installation of injection wells 1-2 through 1-5 (December 2008 and January 2009) did not contain TPHg at concentrations above laboratory reporting limits, which indicates the area of impacted soil is limited in size and/or petroleum hydrocarbons in soil have attenuated. i VM 857\active\7- Eleven\active\185750063_711_14117\05_report_deliv\reports\14117_2013_08_15_closu re_report.doc