THE USE OF PUMPING TESTS TO MEASURE THE VERTICAL HYDRAULIC PROPERTIES OF SEDIMENTARY ROCK FORMATIONS
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An analytical model is presented for the interpretation of pumping tests conducted in a fractured rock aquifer. The solution accommodates multiple horizontal fractures intersecting pumping and observation wells with interconnecting vertical fracture features. The uppermost horizontal fracture is connected via this fracture network to a free surface boundary. Wellbore storage is included at the pumping and observation wells using an approximate superposition technique and the solution is derived using the Laplace transform method. Evaluation is performed by numerical inversion using the Talbot algorithm. Sensitivity of the model to the governing hydraulic parameters for both pumping and observation well data is presented for a realistic range of values for fractured rock. A field example is given to demonstrate the application of the model and to explore the uniqueness of the interpreted values. Based on the results obtained using the present analytical model, estimation of unique values of the vertical hydraulic parameters in a sedimentary rock setting may not be possible using pumping test results. Subsequently, measuring aquifer properties from various testing methods was investigated to explore the significance of fracture heterogeneities relative to tested volumes and to determine which testing methods were capable of producing reliable parameter estimates. The hydrogeological study was performed in a fractured sedimentary rock aquifer using four different field testing methods: constant head tests, pulse interference tests, 12-hour isolated interval pumping tests and 48-hour open-hole pumping tests. Particular emphasis was placed on the reliable estimation of vertical hydraulic parameters in this setting. The evaluation of the pumping test data was performed using the analytical model derived earlier to determine whether the new pumping test model could produce confident estimates of vertical hydraulic parameters. While estimates of horizontal hydraulic conductivity measurements were not affected by test method, open-well pumping tests do not appear able to predict values of vertical hydraulic conductivity and specific yield. Alternatively, pulse interference tests may be a less time-intensive option to constant head injection tests for determining vertical parameters in a sedimentary rock setting.