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bentonite/cement grout to the ground surface. The tremie method will be used to prevent bridging. Potable tap water from a municipal water source will be used for any hydration of any downhole materials. • Leak tests will be conducted with a tracer gas such as isobutane placed near and around the sample train to check for intrusion of ambient air. In the event a leak-check compound is detected in the sample, a different leak-detecting compound will be used for a repeat sample to eliminate the possibility that the first compound is actually present in the soil vapor itself. Soil Gas Sampling • Prior to collecting the soil gas samples, site-specific purging tests will be conducted to determine the appropriate purging volume. Charts of the initial purge tests conducted by the mobile laboratory at the beginning of fieldwork will be provided by the laboratory and included with the analytical results of the soil gas investigation. • Soil gas probes will be placed at two depths, 5 and 15 feet bgs. The final locations of each of the soil gas probes will be determined in the field based on soil lithology and onsite instrument readings. Soil gas sample locations may be moved a certain degree in order to adjust to conditions encountered in the field, but without compromising representativeness of areas of concern such as the UST area. • The soil gas probes will be left undisturbed for a minimum of 30 minutes prior to sampling to allow the soil gas to equilibrate. If possible, the probes will be allowed to equilibrate overnight before sampling. • The tubing exiting the surface of the ground will be connected to a glass sampling bulb fitted with Teflon stopcocks and a viton rubber sampling port. This bulb will be connected in turn to a vacuum gauge, flowmeter, and portable sampling pump. Initially both stopcocks will be closed, and the absence of flow and the presence of a slight vacuum noted. This will demonstrate that the sampling train on the far end of the bulb is leak-tight. Then the first stopcock(pump end) will be opened; the absence of flow will demonstrate that the sampling bulb itself is leak-tight. • The ground end of the bulb will be opened at a flow rate of 150 to 200 ml/min that will be maintained for 7 to 10 purge volumes. Vacuum integrity of the sampling system will also be tested after the soil gas survey using leak-down testing methods as described above. • The soil gas samples will be immediately transferred to the mobile lab for direct injection into a gas chromatograph for analysis of VOCs in accordance with the LARWQCB guidance procedures,by modified EPA Method 8260B. • The analysis of the soil vapor samples will proceed as follows. A 1 ml aliquot of soil vapor will be withdrawn from each bulb and injected into a Hewlett-Packard (HP) model 5890 or 6890 gas chromatograph (GC) interfaced to a HP model 5972 or 5973 mass spectrometer (MS). Chromatography will be performed in such a way that the combination of retention times and mass fragmentation will allow for the complete separation of all of the target compounds. The mass spectrometer will be operated in full scan mode between 35 and 350 amu. This will allow for the identification of any volatile organic species that may be present in the soil vapor. • The following laboratory quality control steps will be performed. An initial five-point calibration will be run. A laboratory control standard (LCS) from Absolute Standards will be run at the end of the same day. The daily standard to be run on each sampling day will also be included in the initial calibration run. The surrogate calibration curve will be run on Aldrich certified material. Compliance with LARWQCB guidance and quality control steps will be documented in the data report. Page 17 PAPEA Lockeford\Work PIan\Lmkeford WP.doc