Detection Of Abandoned Mine Hazards On Government Lands Using Geophysical Methods

Subsurface hazards are numerous in the United States, and are cause for increasing concern. The number of<br>hazardous sites related to previous mining activity on public lands is particularly alarming, and Congress has<br>stated that the problem must be addressed. Specifically, the proclivity of abandoned mine sites on government<br>lands has created dangerous situations in many of our nation’s National Forests, National Park Lands, and on a<br>variety of lands overseen by the Department of the Interior. The affects of subsidence due to historical mining<br>activity can be a long-term economic drain on the limited resources available to maintain roads and trails<br>through these areas. Catastrophic failure and collapse of the ground above old mine workings carries the<br>implication of severe health and safety hazards for hikers, bicyclists, horseback riders and recreational vehicle<br>users. In response to these issues, the U. S. Bureau of Mines has been successful in addressing the problem of<br>subsurface hazard detection and characterization on public lands using geophysical technologies in several recent<br>projects. At the Shawnee National Forest in southern Illinois, in addition to creating dangerous conditions for<br>recreational land users, poorly mapped abandoned tripoli mines pose a potential problem for future logging<br>operations. Old mine workings have been collapsing in certain areas on the property and introduction of the<br>heavy equipment associated with logging may be dangerous. An integrated geophysical investigation, including<br>ground penetrating radar, common offset seismic reflection profiling and magnetic gradient surveying was<br>implemented in attempts to remotely identify the subsurface workings. At the Prince William Forest Park in<br>Virginia, speculation regarding both the location and structural integrity of the main shaft of an abandoned<br>pyrite mine required that some investigation be made. Electrical and magnetic geophysical methods were used<br>to locate the shaft and to assess shaft conditions.