Borehole Geophysical Applications in Karst Hydrogeology

Geophysical measurements in boreholes provide useful information about subsurface aquifers, but the heterogeneity of karst aquifers poses a real challenge in conventional well logging. Borehole geophysics presents several tools that may be applied to the characterization of heterogeneous karst aquifers: (1) Image and flow logs provide detailed information about the nature of hydraulically active zones intersected by boreholes; (2) Geometric correlation of logs between boreholes indicates possible connections between the zones in separate boreholes; (3) Water-quality and hydraulic-head data derived from logs can be used to identify subsurface flow paths; (4) Crossborehole flow experiments can be used to infer the properties of hydraulic connections among subsurface conduits; and (5) Geophysical measurements can be made at local, intermediate, and large scales to infer the relation between scale and hydraulic conductivity. Examples of these applications are given for karst or karst-like aquifers at sites in Arizona, Illinois, Kentucky, New Hampshire, and Florida, demonstrating the specific contributions that borehole geophysics can make in karst characterization.