CHARACTERIZATION OF THE HYDROGEOLOGIC FRAMEWORK OF THE BIG SIOUX AQUIFER, SIOUX FALLS, SOUTH DAKOTA, USING AIRBORNE ELECTROMAGNETIC DATA

Characterization of the Hydrogeologic Framework of the Big Sioux Aquifer, Sioux Falls, South Dakota, using Airborne Electromagnetic Data

Kristen O’Connor¹, Bruce Smith², Joshua Valder¹, David Smith², Greg Delzer¹, Maryla Deszcz-Pan²

¹U.S. Geological Survey, Dakota Science Center, 1608 Mountain View Road, Rapid City, SD 57702

²U.S. Geological Survey, Crustal Geophysics and Geochemistry Science Center, Federal Center, Box 25046, MS 964, Denver, CO, 80225-0046

 

 

Aquifer vertical and horizontal extents typically are determined by interpreting geologic information from drillers’ logs and surficial geology maps. Unfortunately, well and bore-hole data only provide hydrogeologic information for a single point. Airborne electromagnetic (AEM) surveys offer nearly continuous geophysical data along flight lines, which can be related to hydrogeologic conditions. Data collected using AEM, coupled with, and constrained by well and bore-hole data, can significantly improve the accuracy of aquifer hydrogeologic frameworks. More accurate hydrogeologic maps will result in better groundwater models. A current groundwater modeling project for the City of Sioux Falls is being conducted in coordination with the USGS Dakota Science Center, and the USGS Crustal Geophysics and Geochemistry Science Center. Airborne data were acquired using the RESOLVE frequency-domain AEM system to map the Big Sioux Aquifer. The City of Sioux Falls initiated the study to assess its current water resources.

This AEM survey characterized the Big Sioux aquifer, which provides about half of the potable water to the Sioux Falls area. The survey acquired data collected over a total area of approximately 145 square kilometers, primarily over the floodplain of the Big Sioux River between the cities of Dell Rapids and Sioux Falls. The USGS processed the survey data (resistivity-depth inversions) to generate resistivity-depth sections used in 2D maps and in 3D volumetric visualizations of the earth resistivity distribution. Contact lines were drawn using ArcGIS to delineate interpreted geologic stratigraphy. The contact lines were converted to points, and then transformed into a 3D surface. This presentation describes the methods used for the interpretation of AEM resistivity profiles along the Big Sioux Aquifer near Sioux Falls, South Dakota.