Early Earth Science Activities in the Sanford Underground Science and Engineering Laboratory at Homestake

On July 10, 2007, the former Homestake Mine, Lead, South Dakota, was selected as the development site for the Deep Underground Science and Engineering Laboratory, to become the Sanford Underground Science and Engineering Laboratory at Homestake. Work on refurbishment and certification of the Ross Shaft began in August 2007 to effect pumping of water that had reached the 5000 level in late July. Completion of this work will allow a physics and geosciences laboratory to be constructed on the 4,850 ft level (1,478 m from the surface). Concurrent with reentry operations, several earth science research activities have been initiated. These early activities are as follows: (1) Seismic monitoring system: Accelerometers will be installed in surface boreholes and underground drifts as they become available as a result of the reentry work. (2) Evaluation of the 300 level (91 m), which has multiple locations for horizontal access, is ongoing. This near- surface level, with varying overburden thicknesses, offers excellent opportunities to investigate the "critical zone" in terms of hydrology, ecology, and geochemistry, yielding measurements of both moisture and carbon fluxes to evaluate fluid exchanges with the atmosphere. (3) Water and soil samples were collected in the Ross Shaft as part of the first reentry work. Molecular survey of microbial diversity showed the presence of mesophilic and thermophilic cellulose-degrading microorganisms. (4) Supercritical carbon dioxide injection experiments are being planned that will take advantage of three pairs of existing, nearly vertical, open 8-inch (0.2 m) boreholes that are easily accessible from the Ross Shaft. The candidate holes are located between the 1550 and the 2900 levels and are between 90 to 180 m in length (5) Monitoring of the response of the water during the dewatering operations will be facilitated by the use of existing boreholes. Ultimately, the dewatering operation provide access to the 8000 level (depth of 2,438 m), the deepest level. These five examples of ongoing research activities should provide a basis for many other earth science and engineering investigations at this multilevel facility, which already has extensive underground workings. These examples address different aspects of three main themes identified as important by deep underground research communities: restless earth for geo-science, ground truth for geo-engineering, and dark life for geo-microbiology.