Use of the AquaTrack™ technology to identify potential preferential groundwater flow paths in a gypsum-rich bedrock unit

Abstract

Determining the location of preferential groundwater flow paths is highly challenging in most fractured bedrock settings. AquaTrack™ is a surface geophysical method patented by Willowstick® Technologies, LLC, that can be used to identify potential preferential groundwater flow paths within the saturated zone. A circuit is created within the subsurface by passing an alternating electric current between two strategically placed electrodes. The distribution of electric current is influenced by variations in the porosity and permeability of the subsurface materials and the conductance of the groundwater. The magnetic field produced by the electric current can be measured at the surface and compared to the magnetic field expected for a homogeneous case. Significant deviations suggest the presence of heterogeneities, which can be modeled to gain additional insights. An example is presented, where AquaTrack™ was used to identify potential preferential groundwater flow paths in a gypsum-rich bedrock unit located more than 38 m below an industrial facility in upstate New York. Swallets are common in the area and appear to feed the deep bedrock hydrogeologic system. Data from existing bedrock wells show that the permeable gypsum-rich unit is about 1.9 m thick and is saturated on a year-round basis. The groundwater within the unit is about twice as conductive as in the overlying carbonates. The study was performed over a 39 ha area to help determine the placement of additional bedrock wells. Results of the AquaTrack™ survey and associated modeling indicated that groundwater flow within the gypsum-rich bedrock unit was more homogeneous than expected, but four potential preferential groundwater flow paths were identified. Six additional bedrock wells were subsequently installed; five wells were located within the modeled “channels”, and one well was deliberately located outside of the channels for comparison purposes. Another AquaTrack™ study has been performed to extend the original survey area to the south, again to help determine the placement of additional bedrock wells.