Case Studies - Environmental

Mapping Contaminant Pathways and Fracture Systems Around Abandoned Mines: Sulphur Bank Mine, California

In August, 2000, the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA) in conjunction with TetraTech EM Inc., contracted Fugro Airborne Surveys to conduct an airborne Electromagnetic (EM) survey at the Sulphur Bank Mine in Lake County, California. 

Airborne and ground geophysical data were used to improve their knowledge of mine drainage, contaminant sources and contaminant pathways through fracture systems. The airborne survey mapped geological structure on land and below the lake as well as lithology and geological structure on land and under water. This was used to identify natural conduits for the movement of groundwater. The data also showed that acidic water and mercury from the mine are contaminating the lake.

Apparent   Conductivity  56,000 Hz---> 25,000 Hz---> 6,200 Hz---> 900 Hz--->

Acidic water is more conductive than fresh water so the faults, permeable rock layers, and soil that contain acidic water are anomalously conductive. The figures above and below shows the apparent conductivity draped on the topography. The mountains are in the background and the lake is in the foreground. 

The acidic contamination can be detected on land, and where it is leaking into the lake (see figure below). Lower frequencies were used to generate deeper layers, providing a three-dimensional map of the conductivity distribution. The conductivity anomaly in the deeper data is caused by drainage along a deep fracture, which would possibly not have been detected with a shallow ground EM survey. These data will be used to guide further investigation and to position drilling and monitoring wells for monitoring to verify the water flow and acidity.

Apparent Conductivity