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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

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A Sample-Freezing Drive Shoe for a Wireline-Piston Core Sampler

by

Fred Murphy (U.S. Geological Survey, Menlo Park, Calif.) and W.N. Herkelrath (U.S. Geological Survey, Menlo Park, Calif.)

Abstract

The loss of fluids and sample during retrieval of cores of noncohesive sediments results in incorrect measures of fluid distributions and a less-than-ideal measure of the stratigraphic position of the sample. In order to reduce these errors, a hollow drive shoe was developed that allows freezing in place the lowest 75 millimeters of a 48-millimeter-diameter, 1.5-meter-long sediment sample taken using a commercial wireline piston-core sampler. The end of the core is frozen by piping liquid carbon dioxide at ambient temperature through a steel tube from a bottle at the land surface to the drive shoe where it evaporates and expands, cooling the interior surface of the shoe to about -70 C°. The freezing process takes about 10 minutes. This device was used to collect samples for a study of oil-water-air distributions in unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota. Before freezing was employed, samples of sandy sediments from near the water table sometimes flowed out of the core barrel as the sampler was withdrawn. Freezing the bottom of the core ensured the retention of all material that entered the core barrel and lessened the redistribution of fluids within the core.

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