Characterization of the Spiritwood Valley Aquifer, North Dakota, Using a Helicopter Time-domain EM System

Abstract

Summary Buried valley aquifers, consisting of permeable sand and gravel deposits in eroded bedrock valleys, are important sources of groundwater supply in many regions of the United States and Canada. But they have been difficult to define because they are often partially eroded, have complex lithology and are hidden within thick glacial overburden. Recent investigations of the Spiritwood Valley aquifer in Manitoba by the GSC using helicopter time-domain EM have provided the impetus for the North Dakota State Water Commission to fly a VTEM helicopter TDEM survey in the Jamestown, ND region in October, 2016. The VTEM data collected over the Spiritwood-JT block allowed for geological mapping from near surface to depth, in spite of relatively weak resistivity contrasts (<10X). The VTEM data were inverted with the 1D GALEISBSTDEM algorithm to produce resistivity-depth models. These models were able to resolve the location and depths to the top and bottom of the Spiritwood aquifer throughout the central portion of the block providing more detailed pictures of the aquifer’s geometry. In addition to resolving the main Spiritwood aquifer as well as its deeper channels, the VTEM data and models highlighted several smaller aquifers which cross-cut/branch-off from the main Spiritwood channel.