From Ground Water Currents, July 1995, Issue No. 12

New Wellhead Analytic Model

A new computer program has been developed to determine time-of-travel capture zones in relatively simple geohydrological settings. The Wellhead Analytic Element Model (WhAEM) contains an advanced algorithm for determining capture zones for any well at any time based on precise knowledge of the locations of all stagnation points and dividing streamlines. No models currently in use for wellhead protection contain such an algorithm. WhAEM differs from existing analytical models in that it can handle fairly realistic boundary conditions such as streams, lakes and aquifer recharge due to precipitation.

It has features that make the inclusion of open or closed, head-specified boundaries possible (for example to model streams). The newly developed model will serve ground water professionals who wish to determine capture zones in relatively simple geohydro-logical settings. WhAEM consists of two executables: the preprocessor GAEP and the flow model CZAM.

The preprocessor GAEP is designed to simplify the procedures for getting data into a ground water model; specifically it facilitates the interactive process of ground water flow modeling that precedes capture zone delineation. GAEP separates the time consuming (but routine) task of digitizing hydrography data from the creation of conceptual models and subsequent analytic element input data files. With GAEP, the modeler is free to concentrate on interpretation of modeling results rather than the details of data modification and entry into CZAEM. The new algorithms developed for the accurate delineation of capture zone boundaries are implemented in the computer code CZAEM, which accurately defines capture zone boundaries. The WhAEM package is documented in various ways. The primary documentation is contained in a program manual, which includes installation instructions, program descriptions and a tutorial for the integrated use of GAEP and CZAEM. Reference manuals for both GAEP and CZAEM