Determining Potential Contaminant Flow Paths in Karstic Environments: A Minimally Invasive Approach

The difficulties of determining the potential flow paths of subsurface aqueous systems pose a central obstacle to the task of remediating groundwater contamination. This problem is increased dramatically by the structural complexity of karstic environments.  Drilling-intensive approaches to karst characterization are both ecologically traumatic and relatively inefficient.  The minimally invasive methodology detailed in this presentation—which does not require the extensive use of bore holes—is particularly well suited to the modeling of karstic systems.
            This procedure, which uses Audio Frequency Domain Magnetics (AFDM), begins by charging the groundwater site with a low voltage, low amperage, high frequency electrical current.  As the current moves through the groundwater, it emits a magnetic field whose size, shape, magnitude and direction are characteristic of the surrounding aqueous system (Biot-Savart Law).  This field is then read at the surface by a specially tuned receiver.   The data thus generated can be used to create both two-dimensional maps and three-dimensional models which indicate the attributes of the subsurface water network, including potential flow paths. 
This procedure also indicates the location of high levels of Total Dissolved Solids (TDS). Since TDS levels often correspond to the prevalence of certain contaminants, this feature of the AFDM investigation enhances its suitability for the characterization of contaminated groundwater sites and the identification of pollution plumes.
            This technology has recently been deployed in a variety of settings, from ecologically sensitive environments in northern California to complex karst terrain in the Midwest. This presentation will discuss both the science behind the methodology and the lessons learned from its recent applications.