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1 <br /> Tracer Research Ccrporation <br /> tl <br /> r� desired depth, the probes were withdrawn several inches to permit water to flow into <br /> the resulting hole. The aboveground end of the sampling probes were fitted with a <br /> r' vacuum adaptor (metal reducer) and a length of polyethylene tubing leading to a <br /> vacuum pump. A vacuum of up to 22 inches Hg was applied to the interior of the <br /> probe for 10 to 1�minutes or until water was drawn up the probe 'ne water <br /> accumulated in the hole was removed by vacuum through a 114-inch polyethylene <br /> --� tube inserted down into the probe to the bottom of the hole Because the water is <br /> induced to flow into a very narrow hole, it can be sampled with little exposure to air <br /> and, consequently, the loss of volatile compounds by evaporation is reduced The <br /> polyethylene tubing was used only once and discarded to avoid cross contamination <br /> Groundwater samples were collected in 40 milliliter (mL) VOA vials that <br /> were filled to exclude air and capped with Teflon-lined septa caps Approximately <br /> —� half of the liquid in the bottle was decanted, the vials were shaken vigorously, and a <br /> sample of the headspace from the container was injected into the gas chromatograph <br /> (GC) <br /> Indirect (headspace) analysis is the preferred technique when a large number <br /> of water samples are to be performed daily The method is more time efficient for the <br /> E measurement of volatile organics than direct injection of the water sample into the GC <br /> because there is less chance of serru-volatile and non-volatile organics contaminating <br /> the system Depending upon the partitioning coefficient of a given compound, the <br /> indirect analysis method may be more sensitive than the direct injection method The <br /> precision and accuracy of both methods are similar <br /> 5.0 ANALYTICAL PARAMETERS <br /> Up to 10 mL of soil gas and 40 mL of groundwater were collected for <br /> _r- immediate analyses in the Tracer Research analytical van Analytical instruments <br /> were calibrated daily using fresh working standards made from National Institute of <br /> c Sciences and Technology traceable standards and reagent blanked solvents <br /> The GC was calibrated for indirect analysis by decanting 20 mL of the known <br /> standard, leaving approximately the same amount of headspace as in the water <br /> headspace samples The standard bottle was resealed and shaken vigorously for 30 <br /> July 14,1944 <br /> Page 4 114029 IS <br />