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f <br /> Tracer Research Corporation <br /> i <br /> I <br /> contamination as indicated in the soil gas survey. In this manner, soil gas contaminant <br /> mapping can assist in determining the placement of monitoring wells. Thus the likelihood <br /> of drilling unnecessary monitoring wells is reduced. The soil gas survey is not intended to <br /> I <br /> be substitute for conventional methodology, but rather to enable conventional methods to <br /> be used efficiently. <br /> i <br /> �. . EQUIPMENT <br /> Tracer Research Corporation utilized a one ton Ford analytical van that was <br /> equipped with one gas chromatograph and two Spectra Physics computing integrators. In <br /> addition, the van had two built-in gasoline powered generators that provide the electrical <br /> power (110 volts AC) to operate all of the gas chromatographic instruments and field <br /> equipment. A specialized hydraulic mechanism consisting of twocylinders and a set of jaws <br /> I <br /> was used to drive and withdraw the. sampling probes. A hydraulic hammer was used to <br /> assist in driving probes past cobbles and through unusually hard soil. <br /> I <br /> a <br /> i . <br /> SOIL GAS SAMPLING PROCEDURES <br /> jl Sampling probes consisted of 7-14 foot lengths of 3/4 inch diameter hollow steel pipe <br /> that were fitted with detachable drive tips. Soil gas probes were advanced 2-13 feet below <br /> grade. Once inserted into the ground, the above-ground end of the sampling probes were <br /> fitted with a steel reducer and a length of polyethylene tubing leading to a vacuum pump. <br /> Gas flow was monitored by a vacuum gauge to insure that an adequate flow was obtained. <br /> To adequately purge the volume of air within the probe, 2 to 5 liters of gas was <br /> l + evacuated with a vacuum pump. During the soil gas evacuation, samples were collected in <br /> a glass syringe by inserting a syringe needle through a silicone rubber segment in the <br /> I ` <br /> evacuation line and down into the steel probe. Ten milliliters of gas were collected for <br /> immediate analysis in the TRC analytical field van. Soil gas was subsampled (duplicate <br /> 3 <br />