Airborne Electromagnetic Surveys by The U. S. Geological Survey over Concealed Glacial Aquifers, Central United States

The U.S. Geological Survey (USGS) over the last decade has performed several airborne electrical resistivity (helicopter electromagnetic, HEM) surveys over buried glacial features that constitute major aquifers in different regions of the central United States (Figure 1). These surveys have been conducted to map geology, contaminants, and hydrogeology for groundwater studies. Glacial deposits also can contain significant aggregate resources in the United States (Langer, 2002). This paper summarizes the USGS HEM applications in three different glacial terrains. The HEM systems applied in the surveys described here used frequency domain methods that, in electrically conductive areas may be limited to mapping depths less than 60 m. The frequency range typically is from about 100,000 Hz to 400 Hz.