AN EXCEL APPLICATION FOR EVALUATION OF PUMP TEST DATA FOR CONFINED AQUIFERS

There are multiple techniques to evaluate the transmissivity and storativity of confined aquifers. The Theis equation is used frequently in the case of a purely confined aquifer. In confined aquifers with leakage across the confining layer, the Hantush-Jacob equation is used. The application of both of these techniques is similar. They require matching a drawdown curve to a theoretical Theis or Hantush-Jacob type-curve, depending on the application.

Computer applications have been developed for both methods. We have developed an application using an Excel macro that allow analysis of pump test data on Excel. Since Excel is readily available at most universities and colleges, these applications can be used easily without specialized software.

The well function that is used in the Theis test is easily calculated. It is an exponential integral of the first order. There are many simple analytical solutions that accurately calculate this well function. The integral in the Hantush-Jacob well function is more difficult to calculate. It does not lend itself to simple analytical solutions.

The Gauss-Legendre quadrature technique is frequently used to evaluate the Hantush-Jacob well function. Calculation of the Hantush-Jacob function can easily be completed using R. The integration function in R employs the Gauss-Legendre quadrature method for evaluation integrals. After calculating the Hantush-Jacob well function using R for a variety of different u and r/B values, we exported the results to Excel to provide a template for the Hantush-Jacob test.

In Excel, for both the Theis and Hantush-Jacob curves, we developed an application with which one can input the data from pump test. Using the slide bar in Excel, it is possible to adjust the draw down curve to match either Theis or Hantush-Jacob type curves. The calculated transmissivity and storativity are updated constantly as the curves are matched. When the best match is made, one need only note the latest transmissivity and storativity result for the aquifer characteristics.