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Studies concerning the movement and fate of organic chemicals, including hazardous substances, in ground water have underscored the need to use boreholes to obtain samples of ground water that are neither contaminated with foreign materials nor diluted with water from other sources. Additionally, the water samples need to be taken in a manner that prevents the escape of volatile substances. The samples need to be kept close to the original state while in shipment to the water quality laboratory and at the laboratory where the water must be removed from the sample holders without the escape of volatiles or reaction with the air. Within the past year the U.S. Geological Survey has identified its needs for data concerning organics in ground water, and established design criteria for the development of prototype samplers. Certain essential sampler design criteria are: The sampler must go down a 5.1-cm (2 in.) diameter well; the practical sampling depth is at least 61 m (200 ft); the sample holder must be flushed before a sample is taken; and the sample must be kept at the same hydrostatic pressure as when collected.
The Survey is developing prototype samplers using the designated design criteria—a piston sampler operating from a well-logging head, a pumping sampler using a commercial downhole gear pump, a hand-pump sampler, and two electric motor-driven samplers using logging heads. These samplers flush a sample cartridge with the water to be sampled and finally seal the sample prior to being brought to the surface. Later, a design criterion was added that all flush water be removed from the well. New design schemes were drafted that accomplished that requirement. One of the design schemes was a manual sampler which uses a downhole reservoir to collect the flush water. Other design schemes have been envisioned but were found not to be practical. A special sample cartridge that will fit these samplers has been developed to allow removal of the water under pressure. This design helps prevent the escape of volatile substances from the water sample. Fabrication materials include stainless steels, fluoroelastomers, and other fluorinated plastics.
samplers, sampling, ground water, water wells, water pollution, organic wastes, hazardous materials, organic compounds, volatility
Hydrologist, U.S. Geological Survey, Water Resources Division, Hydrologic Instrumentation Facility, National Space Technology Laboratories,