Solutions For A Complex World
Geophysics for Acid Mine Drainage
Article by: Joe Cain | Geologist | hydroGEOPHYSICS
According to the US Environmental Protection Agency, more than half a million abandoned coal and metal mines are discharging acid mine drainage (AMD) into streams, rivers, lakes, and shallow groundwater sources across the US. Acid mine drainage (AMD), or acid rock drainage (ARD) as it is sometimes known, is a severe environmental concern with harmful outcomes for humans and wildlife. AMD occurs when natural precipitation or groundwater flows through exposed sulfide-bearing mineral deposits from the mining process. This interaction produces sulfuric acid, which, in turn, leaches metals left behind in tailings and mine waste, creating an acidic concoction of toxic metals. Acid mine solutions then seep into shallow groundwater or flow into streams, rivers, and lakes, wreaking havoc on biological systems.
Geophysical tools, such as electrical resistivity and electromagnetic methods, offer a cost-efficient and rapid means to map areas of acid mine drainage in the subsurface
Determining the source, subsurface movement, and the extent of this contamination is critical in meeting the needs of any remediation and reclamation project. AMD subsurface pathways are often not easily determined through borehole monitoring or groundwater sampling as these methods may not have a sufficient lateral resolution to pinpoint flow. Geophysical tools, such as electrical resistivity and electromagnetic methods, offer a cost-efficient and rapid means to map areas of AMD in the subsurface, identify sources, track movement, and determine impacted areas.
HGI has developed an AMD geophysical toolbox through decades of experience working with stakeholders to solve AMD challenges. Electrical resistivity and electromagnetic techniques are holistic characterization methods offering broad subsurface AMD mapping of drainage source and direction to assist remediation and reclamation efforts of mine sites. These techniques allow rapid evaluation of subsurface targets, highlighting highly conductive fluids associated with AMD.
Electromagnetic and electrical resistivity techniques non-invasively measure the electrical properties of subsurface materials at depth over areas of concern. Color-contoured maps show electrical property contrasts of differing subsurface geological and hydrogeological conditions targeting AMD flow pathways. Geophysical targeting avoids drilling or excavation, which could create additional problems and increase costs. The techniques can be deployed on mobile platforms to map large areas, hand-carried over rugged or difficult terrain, and collected for subsurface profiles in 2D, 3D, and 4D (monitoring). The resulting geophysical data provides a framework of the underlying hydrogeological, geochemical, and geological conditions beneath a project site, increasing the understanding, magnitude, and controlling factors of AMD movement.
HGI is a world leader in applying, monitoring, and understanding the science of plume mapping using geophysical technologies. Contact us for a free consultation on how geophysics can benefit your next project. We’re always happy to chat – follow us on LinkedIn.
About the Author: Joe Cain | hydroGEOPHYSICS
Joe Cain is a geologist and field project manager with a diverse background of geoscience skills developed over 15+ years as an exploration and resource geologist. He received his Master of Science degree in Geology from the University of California, Davis, in 2006 and Bachelor’s degrees in geology and environmental science from Northern Arizona University.
In addition to geophysical data collection, Joe has provided clients with field services such as drilling oversight of multi-rig campaigns, geotechnical core logging, geologic mapping, and sampling.
Currently, Joe is involved with integrating geologic and geophysical data to support secondary mining recovery, hydrogeologic studies, slope stability studies, and environmental remediation efforts for clients across the Southwestern United States and abroad.