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Tracer Research Corporation I desired depth, the probes were withdrawn several inches to permit water to flow into the resulting hole The aboveground end of the sampling probes were fitted with a vacuum adaptor (metal reducer) and a length of polyethylene tubing leading to a vacuum pump A vacuum of up to 22 inches Hg was applied to the interior of the probe for 10 to 15 minutes or until water was drawn up the probe The water accumulated in the hole was removed by vacuum through a 114-inch polyethylene tube mserted down into the probe to the bottom of the hole Because the water is induced to flow into a very narrow hole, it can be sampled with little exposure to air and, consequently, the loss of volatile compounds by evaporation is reduced The polyethylene tubing was used only once and discarded to avoid cross contamination Groundwater samples were collected in 40 milliliter (mL) VOA vials that were filled to exclude air and capped with Teflon-lined septa caps Approximately half of the liquid in the bottle was decanted, the vials were shaken vigorously, and a sample of the headspace from the container was injected into the gas chromatograph {GC) Indirect (headspace) analysis is the preferred technique when a large number of water samples are to be performed daily The method is more time efficient for the tmeasurement of volatile organics than direct injection of the water sample into the GC because there is less chance of semi-volatile and non-volatile organics contaminating the system Depending upon the partitioning coefficient of a given compound, the indirect analysis method may be more sensitive than the direct injection method The 1 precision and accuracy of both methods are similar 50 ANALYTICAL PARAMETERS Up to 10 mL of soil gas and 40 mL of groundwater were collected for immediate analyses in the Tracer Research analytical van Analytical instruments were calibrated daily using fresh working standards made from National Institute of Sciences and Technology traceable standards and reagent blanked solvents The GC was calibrated for indirect analysis by decanting 20 mL of the known standard,leaving approximately the same amount of headspace as in the water headspace samples The standard bottle was resealed and shaken vigorously for 30 P Jul 19 1994 a&c 4 114M91S Y