Combining Hydraulic Head Analysis with Airborne Electromagnetics to Detect and Map Impermeable Aquifer Boundaries

Abstract

Impermeable aquifer boundaries affect the flow of groundwater, transport of contaminants, and the drawdown of water levels in response to pumping. Hydraulic methods can detect the presence of such boundaries, but these methods are not suited for mapping complex, 3D geological bodies. Airborne electromagnetic (AEM) methods produce 3D geophysical images of the subsurface at depths relevant to most groundwater investigations. Interpreting a geophysical model requires supporting information, and hydraulic heads offer the most direct means of assessing the hydrostratigraphic function of interpreted geological units. This paper presents three examples of combined hydraulic and AEM analysis of impermeable boundaries in glacial deposits of eastern Nebraska, USA. Impermeable boundaries were detected in a long-term hydrograph from an observation well, a short-duration pumping test, and a water table map. AEM methods, including frequency-domain and time-domain AEM, successfully imaged the impermeable boundaries, providing additional details about the lateral extent of the geological bodies. Hydraulic head analysis can be used to verify the hydrostratigraphic interpretation of AEM, aid in the correlation of boundaries through areas of noisy AEM data, and inform the design of AEM surveys at local to regional scales.

Exploring the Model Space of Airborne Electromagnetic Data to Delineate Large‐Scale Structure and Heterogeneity Within an Aquifer System

“…We included these head measurements when assessing what information could be derived from the AEM data about the vertical connectivity of the aquifer system. A similar approach was taken by Korus (2018) to investigate the lateral connectivity of an aquifer system using the AEM method and head measurements.…”

Interpretation of hydrogeologic data to support groundwater management, Bazile Groundwater Management Area, northeast Nebraska, 2019—A case demonstration of the Nebraska Geocloud

“…Many geologic and groundwater studies have included all or parts of the BGMA, including Condra and Reed (1943), Souders and Shaffer (1969), Stanley and Wayne (1972), Gutentag and others (1984), Helgesen and others (1993), Miller and Appel (1997), McGuire and Peterson (2008), Hobza and others (2012), Houston and others (2013), Korus andothers (2013), andStanton (2013). Geologic bedrock maps covering the BGMA have been published by Burchett and others (1988) and Diffendal and others (2008) at the 1:250,000 scale.…”

“…Visualization of the area within Geoscene3D aids in this process. In general, AEM surveying is best suited for mapping regional geologic units (Carney and others, 2015a, b), but researchers have reported the ability to map and detect local confining layers (Korus, 2018). Within the BGMA, we have presented an example (fig.…”

“…Researchers have highlighted the value of continuous water-level interpretation in conjunction with AEM and test-hole data to detect and map confining layers in eastern Nebraska (Korus, 2018). Continuous water-level data (U.S. Geological Survey, 2018a) collected within the BGMA were examined together with the hydrostratigraphic interpretation of AEM profiles in Geoscene3D.…”

Characterize Basin‐Scale Subsurface Using Rocket‐Triggered Lightning

“…Over the past decades, electrical magnetic (EM) surveys have been developed based on airborne, controlled‐source, or natural‐source methods (e.g., Magnetotellurics (MT) and Audio‐frequency MT (AMT)). They have been valuable tools for studying hydrogeological features such as wetlands (McLachlan et al., 2021), aquifers (Koganti et al., 2020; Korus, 2018), volcanoes and geothermal areas (Árnason et al., 2010), hydrocarbon reservoirs (He et al., 2010; Mansoori et al., 2016), ore deposits (Tuncer et al., 2006), salinity mapping (Cox et al., 2012), and fault systems (Tietze & Ritter, 2013). Generally, the artificial EM surveys are suitable for shallow depths and small areas, while the MT yields general locations of anomalies at depth with little detail.…”