Verification of Sampling Methods and Selection of Materials for Ground-Water Contamination Studies

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Abstract
The development of proven sampling methods which incorporate the use of noncontaminating materials has progressed steadily in the past five years. Once the hydrogeologic conditions and potential contaminant source characteristics have been identified at a particular study site, the selection of drilling methods, suitable sampling mechanisms, and appropriate materials must be made for the chemical constituents of interest. The results of laboratory and field testing of sampling mechanisms, tubing and well casing materials, and sampling procedures have identified elements of sampling protocols which are effective in reducing sampling bias and imprecision. The proper selection of these elements bears on the accuracy and precision of all subsequent measurements, since field blanks, sample splits, replicate samples, and standards can only account for errors which occur after sample collection. The limited laboratory and field studies of sampling error strongly suggest that poor borehole seals and improper well purging techniques are serious sources of bias for chemical constituent determinations. Sampling mechanisms and materials are also potential sources of bias, particularly for pH and gas-sensitive parameters and volatile organic compounds. Quality assurance must begin with the decisions made in establishing a sampling point (that is, well or dedicated installation) and collecting samples.