FORCED-GRADIENT TRACER TESTS AND INFERRED HYDRAULIC CONDUCTIVITY DISTRIBUTIONS AT THE MOBILE SITE

Four single-well tracer tests and a two-well tracer test performed in a 21-m thick confined granular aquifer at a field site near Mobile, Alabama, are described. The data from these tests together with previously published data from a single-well test and a two-well test allow one to begin to develop a three-dimensional picture of the hydraulic properties of the study aquifer. A consistent feature of all the tests is a high hydraulic conductivity zone which appears in the bottom third of the aquifier. In some locations the new tests indicated high hydraulic conductivity zones in the upper third of the aquifier which were not detected in the previous two-well test and single-well tests. It was possible to predict the major features of the tracer concentration as a function of time at the withdrawal well in the two-well test by means of an available numerical model assuming perfect stratification at the test site and using a hydraulic conductivity distribution inferred from a single-well test. Additional study results are discussed.