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! Tracer fearch Corporation r through a 6-inch asphalt cover. The depth to groundwater is 15 to 20 feet below grade. The direction of groundwater flow is unknown. �f 3.0 SAMPLING PARAMETERS Soil gas sampling probes consisted of 7-foot lengths of 314-inch diameter hollow i, a steel pipe. -.After the sampler drilled through 6 inches of asphalt, all of the probes were hydraulicallypushed to the desired.depth. The probes were fitted with detachable drive tips and advanced 2 to 5 feet below ground surface (bgs). The aboveground end of each probe # was fitted with an aluminum reducer (manifold) and a length of polyethylene-tubing leading to a vacuum pump. Soil gas was pulled-by the vacuum pump into the probe. Samples were k collected in a lass sYr-n e b'y inserting.a syringe needle through a silicone rubber segment in the-evacuation line and down into the steel probe. The vacuum was monitored by a . vacuum gauge to ensure an adequate gas flow from the-vadose zone was maintained. The volume of'air within the probe was purged by evacuating 2 to 5 probe volumes of gas. The evacuation time in minutes versus the-vacuum in inches of mercury (Hg) was used to calculate the necessary evacuation time. The vacuum in inches Hg.was recorded.at each sampling location. The ma-ori of the sam le robe vacuums were 3 to 15 inches H Samples SG-2 majority P P g• P and SG-17 had a vacuum of 18 inches Hg. Samples SG-6, SG-12, SG-13,and SG 16 had vacuums from 20 to 24 inches Hg. The maximum,vacuum recorded was 27 inches Hg. 4.0 ANALYTICAL PARAMETERS During this investigation, 2 to 10.milliliters.(ml) of soil gas were collected for each sample for immediate analysis in the analytical van. Subsamples (duplicates) from these samples were injected.,into the GC in volumes of 1 to 500 microliters (ul). 1 f k 1 May 21';1992. Page 2- 1.92-302