The Unreliability of Open Observation Boreholes in Unconfined Aquifer Pumping Tests

ABSTRACT Initial attempts to estimate unconfined aquifer parameters from a pumping test using an open observation borehole proved to be unsuccessful. However, when separate piezometers were installed along a vertical section, significant differences in ground‐water head were noted. These differences suggest that rather than providing an average ground‐water head, the open borehole provides a means of flow between the different elevations and therefore produces misleading results. The results for the separate piezometers are analysed using a numerical model, and reasonable values of the aquifer parameters are deduced.