F.P. Haeni 1995 Combined use of seismic-refraction, direct-current resistivity, very-low-frequency terrain-resistivity, and inductive terrain-conductivity methods were demonstrated at sites in Connecticut, New York, and Maine. Although no single method can define both the hydrogeologic boundaries and general grain-size characteristics of sand and gravel aquifers, a combination of these methods can. Comparisons of measured electrical properties of aquifers with logs of test holes and wells indicate that, for a given conductivity of ground water, the bulk electrical resistivity of aquifers in the glaciated Northeast increases with grain size. application/pdf 10.3133/pp1415A en U.S. Geological Survey Application of surface-geophysical methods to investigations of sand and gravel aquifers in the glaciated Northeastern United States reports