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Volume 42, Issue 5 (September 2019)
Disagreeing Evaluations for Slug Tests in Monitoring Wells: Importance of Standards
(Received 3 March 2016; accepted 7 June 2018)
Published Online: 16 October 2018
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Hundreds of variable-head permeability (slug) tests were carried out in monitoring wells to assess the hydraulic conductivity, K, of an unconfined sand-and-gravel aquifer and, after that, the migration of contaminants. The pollution case has generated a legal dispute about the loss of many water supply wells and major health issues. The experts for the defendants had analyzed the slug test data with methods that differ from the standards. For the legal issues, the author reanalyzed all test data and made all verifications as required by standards. The new K values were about three times higher than the initial values obtained without respect to the standards, a major difference. The divergence was solved by studying the statistical distributions of K values. The initial values were too low to explain the high K values obtained with pumping tests, but the new K values correctly explained them. The new K values predicted groundwater velocity values at least three times higher than the initial values predicted with K values obtained without following the standards. These higher velocities were confirmed by field tracer tests performed by independent companies that designed and operated field pilot tests for decontaminating groundwater. The capacity to reconcile medium-scale tests (slug tests in monitoring wells) and large-scale tests (pumping tests in large wells) forms new evidence that strengthens the reasons for why it is important to follow the standards and make the required verifications.
Chapuis, Robert P.
Department of Civil, Geological and Mining Engineering, École Polytechnique, Montreal, QC
Stock #: GTJ20160046
Title Disagreeing Evaluations for Slug Tests in Monitoring Wells: Importance of Standards