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' . • <br /> b. Organic lead: Tetraethyl/tetramethyl-lead are volatile; <br /> therefore, soil samples should be collected in cylinders and <br /> frozen as described for volatile hydrocarbons above. <br /> C. Shipping Samples: Where commercial shippers are involved, <br /> dry ice may present Department of Transportation (DOT) <br /> shipping problems and "blue ice" may have to be substituted. <br /> 3. Water Samples <br /> a. Free floating product (from a well) : Sampling of free <br /> floating product on the surface of ground water should not <br /> be performed until the well has been allowed to stabilize <br /> for at least 24 hours after development or other withdrawal <br /> procedure. A sample should be collected that is indicative <br /> of the thickness of floating product within the monitoring <br /> well. This may be accomplished by the use of a clear, <br /> acrylic bailer designed to collect a liquid sample where <br /> free product and ground water meet. A graduated scale on <br /> the bailer is helpful for determining the thickness of free <br /> product. Samples should be field-inspected for the presence <br /> of odor and/or sheen in addition to the above evaluation. <br /> Electronic measuring devices also are available for deter- <br /> mining the thickness of the hydrocarbon layer floating on <br /> ground water. <br /> b. Dissolved product (from a well) : If free product is <br /> detected, analysis of water for dissolved product should be <br /> conducted after the free product has been substantially <br /> removed from the well. Before collecting a water sample, a <br /> well should be purged until temperature, conductivity and pH <br /> stabilize. Often, this will require removal of four or more <br /> well volumes by bailing or pumping. Once well volumes are <br /> removed and well water is stabilized, a sample can be taken <br /> after the water level approaches 80 percent of its initial <br /> level. Where water level recovery is slow, the sample can <br /> be collected after stabilization is achieved. <br /> Ground water samples should be collected in a manner which <br /> reduces or eliminates the possibility of loss of volatile <br /> constituents from the sample. For collecting samples, a <br /> gas-actuated positive displacement pump or a submersible <br /> pump is preferred. A Teflon or stainless steel bailer is <br /> acceptable. Peristaltic pumps or airlift pumps should not <br /> be used. <br /> Cross-contamination from transferring pumps (or bailers) <br /> from well to well can occur and should be avoided by thor- <br /> ough cleaning between sampling episodes. Dedicated (i.e. , <br /> permanent installation) well pumps, while expensive, are <br /> -61- <br />