Combined interpretation of pumping and tracer tests: theoretical considerations and illustration with a field test

Pumping and tracer tests are two well-established ground water reservoir tests. Hydraulic conductivity can be derived from both. Conductivities are studied in a mainly layered heterogeneous coastal aquifer in Belgium with a pumping and tracer test and results of both are compared. Characteristics and important points in performance and interpretation of the tests are discussed. The interpretation method of pumping tests must be chosen very carefully. Application of interpretation methods based on models underestimating or even neglecting the leakage towards the pumped permeable layer results in an overestimation of the horizontal conductivity of this layer. The larger the distance of the used observation well(s), the larger this overestimation becomes. This is illustrated here with the interpretation of the drawdown data obtained during the pumping test using different analytical models and a numerical model. With an inverse axi-symmetric numerical model incorporating layered heterogeneity, results of the pumping test are in good agreement with results from the tracer test. Many discrepancies between pumping and tracer test data performed in layered heterogeneous media can be explained when realistic pumping test interpretation methods are applied and when leakage is not underestimated.