Large-scale TEM investigation for groundwater

Abstract

The transient electromagnetic (TEM) method has proven to be a powerful tool for the delineation of water-bearing sand and gravel layers in hydrogeophysical investigations. Advancements in the technique include newly developed TEM systems?the Pulled Array TEM (PATEM) and the High Moment TEM (HiTEM) systems?along with innovations in data interpretation. The advanced methodology is illustrated in two case histories. The first, a large-scale TEM survey northwest of Aarhus, Denmark, includes more than 2700 conventional 40 m ´ 40 m TEM soundings and approximately 500 km of PATEM data. Thematic maps of interval resistivities and depth to low-resistivity Palaeogene clays provide a detailed view of the hydrogeological conditions in the area. The second is a groundwater investigation at Hedensted, Denmark. Based on the hydrogeophysical survey, a new well field in this area was located and developed. The initial phase of the survey included 500 TEM soundings. Based on the interpretation of the TEM survey, two seismic sections were acquired across formerly unknown aquifers. The seismic data made it possible to select optimal locations for three wells that were drilled subsequently. The new well field yields up to 400 000 m3 water/year.