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05-2000 17:58 FRO ECISION SAMPLING iu l�llJtiJ�4J�� r.�� <br /> withdraw the content from the casing. The initial withdrawal from the casing is audible; <br /> once the "hiss" diminishes the amount of vacuum remaining in the canister is All <br /> considerable. The time of sample collection varies in different formations. Within clay <br /> environments, soil vapor collection may take as long as several minutes. In sandy <br /> environments, soil vapor collection time may be less than one minute. Clay and sand <br /> represent the two permeability extremes in subsurface environments. In order to <br /> measure the amount of vacuum remaining in the canister, a gauge is connected inline. <br /> In some instances a second gauge is used to measure and regulate the amount of <br /> vacuum pressure being drawn from the formation. The client supplies the gauges for <br /> measuring the amount of vacuum. <br /> Decontamination <br /> Soil gas sampling or soil vapor extraction sampling using PRT equipment is very simple <br /> to decontaminate. The formation is cleaned off the rods as well as the retractable tip <br /> assembly. New tubing is prepared with the reverse threaded nipple while re-entering <br /> the boring for additional soil gas samples at greater depths. <br /> Temporary Installation <br /> Any of the methods described above would be used to install a temporary sampling <br /> point. The boring is cased-off with the Envirocore or smaller diameter casing for the day. <br /> Any period of time longer than the amount of time onsite would require a permanent <br /> installation. <br /> I✓C-4 soit,mss 12 <br /> TOTAL P.05 <br />