FROM BASIC PHYSICS TO COMPLEX HYDROGEOLOGY: A UNIQUE APPROACH FOR DERIVING HYDRAULIC CONDUCTIVITY IN AN UNDERGROUND LAB

The Sanford Underground Laboratory is the interim facility for the future federally funded Deep Underground Science and Engineering Lab (DUSEL). The lab is situated in Precambrian metasedimentary and metavolcanic rocks intersected by Tertiary dike swarms. The Homestake mine was closed in 2001 and the pump system keeping the mine dry was turned off in 2003. By 2008 the water level had risen 3470 ft in the 8000-ft deep mine. Reactivation of the pump system in 2008 has led to a reduction in water level of more than 500 ft. Investigation of previously flooded areas has revealed that iron dissolved in the water oxidized as the mine flooded, staining the submerged rocks; however, isolated air pockets have been identified by long stretches of unstained areas along the top of tunnels and other openings. A new approach is being tested to determine rock permeability through analysis of air pocket properties in several rock formations and multiple depths. Combining the ideal gas law, Darcy's equation, and field measurements, a model has been created to determine the mass of air forced from the air pocket into the rock matrix over a period of time. Hydraulic conductivity values will be derived, based on the volume of gas lost into the rock.