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' or electric rotary hammer. Once inserted to the desired depth, the probe will be rotated in a clockwise direction, or retracted slightly, opening the tip and exposing the vapor sampling ports. Soil vapor will be withdrawn from nylaflow tubing using a small calibrated syringe, connected by an on-off valve. The fust 5 dead volumes of gas will be discarded to flush the sample tubing and fill it with in-situ soil vapor. The next 20 cc of soil vapor will be withdrawn in the syringe, plugged, and transferred immediately to the onsite mobile lab for analysis. Mobile laboratory Services will be provided by Transglobal Environmental Geochemistry (TEG). High vacuums and flow rates will be avoided to minimize the chances of leakage (<200mllminute). Purging will also be minimized to ensure that samples represent VOC concentrations at the sampling tip. ' 2.3.2 Soil Gas Sample Analysis 2.3.2.1 Analytical Methods. Soil vapor samples will be analyzed for VOCs using EPA Method 8010, and analytical results will be produced on a "real time' basis. The samples will be analyzed on a gas chromatograph (GC) equipped with megabore columns and an appropriate combination of electrolytic conductivity (ELCD), photoionization (PID), flame ionization (FID) and electron capture (ECD) detectors. Detectors are be used in series to give dual detector confirmation of compounds. A surrogate compound will be added during analysis to confirm that the chromatographic retention times have not shifted. Output signals will be processed by computer chromatography software and the results entered into a laboratory computer for on-site processing and graphing. A detection limit of not more than 1 µg/L for PCE and TCE will be attained. When a measured concentration is greater than 50% of the highest concentration in the calibration range,the sample will be reanalyzed using a smaller volume or dilution. 2.3.2.2 Quality Assurance/Quality Control. The GC will be calibrated daily at the start and end of the day. A calibration standard solution, prepared from a separate source, is analyzed at the mid-point concentration immediately after the initial calibration to verify the true concentrations in the calibration standards. In order for the initial calibration to be acceptable, the response factor (RF) (the concentration divided by the chromatographic area counts) must be within+/-15% difference when compared to the average RF of the initial calibration; otherwise the instrument must be recalibrated. Acceptable continuing calibration agreement will be +/-20%. In the event that all sample analyses for the day result in non-detected concentrations of all target compounds, a laboratory control sample at the low-point calibration concentration (1 µg/L) will be analyzed at the end of the day. An ambient blank and a soil gas probe blank samples will also be analyzed at the start of each day; an ambient blank will also be analyzed when measured concentrations of a soil vapor sample is greater than 50% of the highest concentration in the 6