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

Home Browse Search

AECOM Report on Soil Vapor Sampling and Human Health Risk Assessment 2-3 matter what impact moisture may have on soil gas concentrations, as indicated in Section 3.0, we have demonstrated that the excess lifetime cancer risk(ELCR)and hazard index(HI)results are below the Califomia EPA and USEPA's target cancer risk range (1x106 to 1x10') and total HI of 1, for the residential scenario.] On September 9, 2010,AECOM personnel collected vapor samples from vapor well SV-1. No significant(>0.5-inch)rainfall occurred during or immediately prior to (within 24 hours)this event and the ground surface in the vicinity of SV-1 appeared to be dry. Sample SV-1 was collected over a period of 210 minutes (3.5 hours) using a 6-liter Summa canister. The sample collection time of 3.5 hours was due to a low vapor recovery rate and the collection of a duplicate (SV-1D)sample. The collection of a split duplicate sample doubles the collection time since two sampling containersare being filled simultaneously. Sample SV-1 and SV-1 D were collected with a final sampling container vacuum of approximately 17 inches Hg (reported upon receipt at the laboratory to be 16.4 inches Hg). Consequently, the laboratory detection limits increased. One field blank sample (FB-1)was collected by running laboratory-certified zero air through a manifold with a 1-foot length of Teflon tubing connected to the sample container. Sample FB-1 was collected over a period of 30 minutes and was collected with a final canister vacuum of 7 inches Hg. 2.3.1 Analytical Results Air Toxics analyzed a total of two soil vapor samples(SV-1 and SV-1 D)collected from well SV-1.The samples were analyzed for total petroleum hydrocarbons as gasoline(TPHg), naphthalene, and benzene, toluene, ethylbenzene,total xylenes, (BTEX) by Method TO-15. Due to an error at the laboratory, the samples were not analyzed as requested for atmospheric gases (oxygen, methane, carbon dioxide, nitrogen,and helium [as a tracer gas])by modified ASTM Method D-1946, therefore, the sample train integrity during the sampling event could not be verified. Soil vapor analytical resutts are summarized in the table below with references to California Human Health Screening Levels(CHHSLs) (CalEPA, 2005 and 2009)and RWQCB Region II Environmental Screening Levels (ESLs)for a commercial/industrial exposure scenario. CHHSLs for a residential exposure scenario are noted in brackets([]). Duplicate concentrations, where different, are noted in parentheses. No compounds were detected in the field blank. 60146W/ Mt0 December 15,2010