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Interpretation of Ground Water Chemical Quality Data
G. M. Zemansky
Compass Environmental, Inc., 3000 W. 19th Court, Lawrence, Kansas 66047-2300

Paper published in the Proceedings of WTQA '98 (14th Annual Waste Testing & Quality Assurance Symposium), pp. 192-201.

Ground water is sampled to assess its quality for a variety of purposes. Whatever the purpose, it can only be achieved if results are representative of actual site conditions and are interpreted in the context of those conditions. Substantial costs are incurred to obtain and analyze samples. Field costs for drilling, installing, and sampling monitoring wells and laboratory costs for analyzing samples are not trivial. The utility of such expenditures can be jeopardized by the manner in which reported results are interpreted as well as by problems in how samples were obtained and analyzed. Considerable attention has been given to standardizing procedures for sampling and analyzing ground water. Although following such standard procedures is important and provides a necessary foundation for understanding results, it neither guarantees that reported results will be representative nor necessarily have any real relationship to actual site conditions. Comprehensive data analysis and evaluation by a knowledgeable professional should be the final quality assurance step, it may indeed help to find errors in field or laboratory work that went otherwise unnoticed, and provides the best chance for real understanding of the meaning of reported results. The focus of this paper is on the interpretative part of the process. Although formal interpretation necessarily comes late in a project, when data have been generated and the report is being written, it will be most useful if relevant elements can be integrated into the project from the beginning. When this is done, it increases the likelihood of achieving project objectives as well as understanding the data. To facilitate interpretation, the following steps should be included: 1. Collection, analysis, and evaluation of background data on regional and site-specific geology, hydrology, and potential anthropogenic factors that could influence ground water quality and collection of background information on the environmental chemistry of the analytes of concern. 2. Planning and carrying out of field activities using accepted standard procedures capable of producing data of known quality. 3. Selection of a laboratory to analyze ground water samples based on careful evaluation of laboratory qualifications. 4. The use of appropriate quality control/quality assurance (QC/QA) checks of field and laboratory work (including field blank, duplicate, and performance evaluation samples). 5. Comprehensive interpretation of reported analytical data by a knowledgeable professional. The analytical data must be accompanied by appropriate QC/QA data, be cross-checked using standard water quality checks and relationships where possible, and be correlated with information on regional and site-specific geology and hydrology, environmental chemistry, and potential anthropogenic influences. Application of this sequence of steps and their importance in interpretation of ground water quality data are discussed in this paper. The discussion includes several illustrative case examples.

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