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2.2.5 Soil Vapor Sample Collection On November 20 and 24, 2008, Bureau Veritas installed soil vapor probes within BV-4 and BV-5 at 5 feet and 15 feet bgs, and in BV-6 at 5 feet and 12 feet bgs. Soil vapor probes were constructed of Teflon tubing with particulate end filters. Sand packs were placed around the particulate filters and dry bentonite covered the sand packs with intermediate areas of the bentonite seals being hydrated with distilled water using a tremmie pipe, until the borehole was sealed to the surface. The soil vapor probes were allowed to stabilize from 30 minutes to over two hours prior to sample collection. The soil vapor sampling was conducted in accordance with the guidance provided in the San Francisco Bay Area Regional Water Quality Control Board (RWQCB) Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater(RWQCB, 2005), California Department of Toxic Substances Control/Los Angeles RWQCB Advisory—Active Soil Gas Investigations(DTSC/LARWQCB, 2003), and DTSC's Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(DTSC, 2005). The purge volume of the proposed soil vapor monitoring probes and sample manifold was calculated and approximately three volumes of the tubing, probe tip, and sampling manifold were purged prior to sample collection. The sampling and purging systems were setup using a certified clean manifold system with a laboratory-calibrated flow controller connected to a 6 Liter SUMMA TM canister and a purge canister. Each canister had its own vacuum gauge. The SUMMA TM canister flow controllers were requested for a sample rate of 100 to 200 milliliters per minute(ml/min). The SUMMA TM canisters and flow controllers were certified as clean prior to use and were provided by the analytical laboratory. Prior to sampling, a vacuum test was conducted after the sampling manifold and SUMMA canisters were connected to the soil-vapor probe. The valve on the manifold connected to the soil vapor probe and the valve on the sample canister were kept closed while the purge canister valve was opened for a period of 5 to 10 minutes while the pressure gauge on the purge canister was monitored. In each test, no observable drop in pressure was noted. The purge process was then initiated by opening the manifold valve to the soil-vapor probe. After an appropriate drop in pressure(that corresponded to the calculated purge volume)was recorded on the purge canister, the purge canister valve was closed and the sample canister valve was opened to start the sample collection process. The soil vapor samples were generally collected over an approximate '/z hour to one hour period; the actual sample intervals varied from 32 to 72 minutes. Sample BV-6-5'was left open for 215 minutes; however, the soil conditions were tight and no usable sample was collected (total pressure drop was only-5 inches). The initial vacuum in each canister was-30 or more inches of mercury, indicating that the canisters had not leaked prior to sampling. The samples were collected by opening the SUMMATm canister valves and then closing the valves after the sampling period. At the completion of the sampling period,the final vacuum in each SUMMA TM canister was recorded. The initial and final canister vacuums and sampling times were recorded on Soil Vapor Sampling Forms presented in Appendix D. During sampling, a tracer gas(isopropanol)was used as a leak check compound to confirm that the soil vapor monitoring probes and sample train were leak free. This compound was then analyzed for by the analytical laboratory to determine if there were surface or system leaks due to improper installation of the vapor inlet probe or system connections. The soil vapor samples were recorded on a COC document that accompanied the samples from the point of collection to the analytical laboratory. Once the soil vapor samples were collected, the soil vapor sample tubing was withdrawn from the borehole and a concrete surface plug was placed in the upper one-half foot of the boring, which was leveled to grade. 5 Project Number 99008-008321.03