ARCHIVED REPORTS_REPORT ON SOIL VAPOR SAMPLING AND HUMAN HEALTH RISK ASSESSMENT DEC 2010

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AECOM Report on Soil Vapor Sampling and Human Health Risk Assessment 2-7 APH Resutts for SV-1 October 20,2010,Event Carbon Fraction Amount Detected (ppbv) C5-C6 Aliphatic Hydrocarbons(ref to Pentane+Hexane) ND >C6-C8 Aliphatic Hydrocarbons (ref.to Heptane) 990 >C8-C10 Aliphatic Hydrocarbons(ref.to Decane) 120 >C10-C12 Aliphatic Hydrocarbons(ref.to Dodecane) ND >C8-C10 Aromatic Hydrocarbons(ref.to 1,2,3-TMB) ND >C10-C12 Aromatic Hydrocarbons(ref.to 1,2,4,5-TMB) ND A discussion of the laboratory analytical results is provided below in Section 2.5. The laboratory analytical reports, including COC documentation, are included in Attachment B. No helium was detected above laboratory reporting limits in the samples collected during the October 20, 2010, event. 2.5 Discussion of Results The wide variation in TPHg concentrations reported by the laboratory for SV-1 during the May, September, and October 2010 sampling events prompted further investigation of these results.All of the SV-1 data available(chromatograms and TICS)from Air Toxics with regard to the three sampling events has been obtained. The detailed results (for SV-1 only) are summarized in Table 1 (attached). The summary table shays the TPHg results from SV-1 for each sample event. These results indicate very low to non-detected concentrations of the principal aromatic components of gasoline(i.e., BTEX) in contrast with the relatively high TPHg results. The TICS from all three sampling events show some common components, despite the wide range of TPHg concentrations. The reported TICS are predominantly compounds containing eight carbons in a chain (C8), and do not include any aromatic compounds (composed of carbons in a ring). The identified CS compounds are not abundant in fresh gasoline, and their predominance in the sample indicates that if the source of these compounds was gasoline then its properties have changed substantially. These changes could be attributed to biodegradation. To further determine the nature of the TPHg components and their relationship to gasoline, chromatograms were requested from the laboratory for each of the sampling events (May, September, and October).Chromatography separates mixtures into individual chemical components, because each component'elutes' (comes off of the column and is detected as a'peak')at a time in the'run'speck to its chemical properties (e.g., volatility) and interactions with a chromatographic column. This provides a`picture' of the mixture based on its individual separated components. TPH analytical methods(e.g.,TO-15)quantify common mixtures (like gasoline) by combining selected 'peak' measurements (i.e., mathematically re-combining the separated components into one type of mixture), resulting in a detected concentration based on the mixture's cumulative components. TPHg was calculated by the laboratory as the sum of peak areas within a retention time window. However, 6014657&M10 December 15,2010