REEXAMINING SLUG TESTS FOR HIGHLY PERMEABLE AQUIFER CHARACTERIZATION WITH END-MEMBER LABORATORY TESTS AND WELL TESTS

Accurate hydraulic conductivity values are essential for understanding the flow of water and are a key component in understanding and modeling the effects of sea level rise on salt water intrusion in coastal aquifers. A review of reported hydraulic conductivity values for the Biscayne Aquifer suggests that while slug tests are a rapid and cost-effective aquifer testing method, large discrepancies among reported values based on different methods indicate a need to reexamine slug tests as applied to highly permeable materials. To determine the validity of slug tests under highly permeable conditions where the response is usually underdamped, two damped spring mass models for an end-member (aquifer-free) case with oscillating responses are developed and applied to actual well tests and a laboratory case. Selection of appropriate well tests for the application of the models includes selection of test wells constructed with an unscreened test zone and with casing that crosses the water table, tests that exhibit oscillating response, and tests with a water column length larger than the initial displacement. Experimental design of an end-member aquifer-free laboratory case consists of a tank and a partially submerged pipe. Video recordings of the experiments are used to collect the data. Varying tank sizes, pipe sizes, and submergence depths will provide insight into the predictive ability of the simple models. The observations collected from preliminary end-member laboratory measurements agree well with one of the models and actual well tests agree closely with one of the models and reasonably closely with the other model. Analysis of this end-member case and comparison with well tests will allow us to determine if the behavior of some slug tests in highly permeable material can be predicted by the simple models and determine when the estimation of true hydraulic conductivity values in highly permeable aquifers may not be possible with slug tests.