Modeling of ground water infiltration and movement in the wellhead area is a critical part of an effective wellhead protection program. Such models depend on an accurate description of the aquifer in the wellhead area so that reliable estimates of contaminant travel times can be used in defining a protection area. Geophysical and hydraulic measurements in boreholes provide one of the most important methods for obtaining the data needed to specify wellhead protection measures. Most effective characterization of aquifers in the wellhead vicinity results when a variety of geophysical and hydraulic measurements are made where geophysical measurements can be calibrated in terms of hydraulic variables, and where measurements are made at somewhat different scales of investigation. The application of multiple geophysical measurements to ground water flow in the wellhead area is illustrated by examples in alluvial, fractured sedimentary, and fractured crystalline rock aquifers. Data obtained from a single test well are useful, but cannot indicate how conductive elements in the aquifer are connected to form large-scale flow paths. Geophysical and hydraulic measurements made in arrays of observation boreholes can provide information about such large-scale flow paths, and are especially useful in specifying aquifer properties in wellhead protection studies.
