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 2-1 2.0 Soil Vapor Sampling 2.1 Vapor Probe Installation Three soil vapor monitoring wells were installed at the site on May 13, 2010. Details of the well installations are documented in the Report of Soil Vapor Well Installation and Soil Vapor Sampling Activities, prepared by AECOM and submitted to the RWQCB on July 15,2010. 2.2 Soil Vapor Sampling Procedures The following subsections provide general information regarding the procedures followed during collection of the soil vapor samples. Sampling methods followed the procedures presented in the DTSC guidance document(DTSC, 2005)and the NYSDH guidance document(NYSDH, 2005). 2.2.1 Sampling Equipment All gauges and flow control manifolds were supplied by Air Toxics of Folsom, California.The gauges and manifolds were connected by chromatography-grade, stainless steel tubing and dedicated airtight,flexible,Teflon tubing, supplied by the laboratory, that have a low capacity for adsorbing volatile organic compounds (VOCs). In order to draw the soil vapor to the surface, a vacuum was created using an evacuated Summa® canister, supplied by Air Toxics. A three-way valve was used to isolate the purging canal equip ument separate tube that was connected to the vapor sample canister. Figure 3 shows a typ sample train for the soil vapor sampling activities. Samples were collected in either 1-or 6-liter Summa®canisters provided by Air Toxics and certified at 100% dean for use in human health risk assessment. Each canister was field verified to have a vacuum of at least minus 25 inches of mercury(Hg)prior to sampling. 2.2.2 Leak Testing Leakage of atmospheric air into the equipment during sampling can compromise sample integrity and dilute measured soil vapor hydrocarbon concentrations. Sampling equipment was thoroughly inspected to ensure tight fittings between all components.To minimize the potential for leakage, the soil vapor sampling rate was kept at< 200 milliliters per minute (mLimin) using a flow controller supplied by Air Toxics. Prior to sampling,the Summa®canister valve was opened to the still dosed SwageloW valve for ten minutes and the initial vacuum pressure recorded.The sample train was considered to pass the leak test if constant vacuum pressure was maintained for the ten minutes. Helium was used as the tracer gas to test for air leakage into the sampling system for the purpose of sample integrity verification, in general accordance with the NYSDH guidance document (NYSDH, 2005). A dear plastic chamber was placed over the well head and sealed to the ground surface with a rubber mat. Helium from a cylinder was discharged into the chamber, and a helium December 15,2010 601465 6M10