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Tracer Research Corporation <br /> I <br /> syringe by inserting a syringe needle through a silicone rubber segment in the <br /> evacuation line and down into the steel probe. The vacuum was monitored by a <br /> vacuum gauge to ensure an adequate gas flow from the vadose zone was maintained. <br /> During this investigation, 3 to 9 milliliters (ml) of soil gas were collected for <br /> immediate analysis in the Tracer Research analytical van. <br /> The volume of air within the probe was purged by evacuating 2 to 5 probe <br /> volumes of gas. The evacuation time in minutes versus the vacuum in inches of <br /> mercury (Hg) was used to calculate the necessary evacuation time. The vacuum in <br /> inches Hg was recorded at each sampling location. <br /> Probe vacuums ranged from 2 to 10 inches Hg. The maximum vacuum <br /> reading was 25 inches Hg. <br /> When sample probe SG-413' was removed, a hole was discovered 5 foot <br /> ' down the probe. This could have caused a dilution of the sample. <br /> 4.0 GROUNDWATER SAMPLING PROCEDURES <br /> When groundwater was encountered, water samples were collected. Six <br /> water samples were collected at locations 4, 5, 6, 7, 9, and 10 and analyzed for the <br /> target compounds. <br /> Sampling probes consisted of 7- and 14-foot lengths of 3/4-inch diameter <br /> hollow steel pipe. Groundwater samples were collected at depths of 12 to 14 bgs. <br /> The hollow probes with detachable drive points were driven below the water <br /> table. Once at the desired depth, the probes were withdrawn several inches to permit <br /> water to flow into the resulting hole. The aboveground end of the sampling probes <br /> '1 were fitted with a vacuum adaptor (metal reducer) and a length of polyethylene tubing <br /> leading to a vacuum pump. A vacuum of up to 25 inches Hg was applied to the <br /> ' interior of the probe for 10 to 15 minutes or until water was drawn up the probe. The <br /> water accumulated in the hole was removed by vacuum through a 1/4-inch <br /> polyethylene tube inserted down into the probe to the bottom of the hole. Because the <br /> water is induced to flow into a very narrow hole, it can be sampled with little exposure <br /> to air and, consequently, the loss of volatile compounds by evaporation is reduced. <br /> The polyethylene tubing was used only once and discarded to avoid cross <br /> May 22.1992 Page 2 1-92-358 <br />