3500 Level breakthrough cools deeper levels

LEAD, S.D. -- Technicians have dropped the temperature 19 degrees at the 4,550-foot level of the Sanford Underground Laboratory at Homestake.
The temperature at the 4550 Level had been about 90 degrees. Now it's about 71 degrees.
South Dakota Science and Technology Authority crews, working underground and on the surface, dropped the temperature by making two changes in the ventilation system.
An underground crew used sledgehammers to remove a foot-thick concrete wall in a tunnel on the 3,500-foot level of the former gold mine. "That was tough work," Sanford Lab Engineering Director Todd Seaman said. Knocking out the wall opened a passage to the Oro Hondo Shaft, which runs from the surface to the 4,100-foot level.

Another crew restarted a large exhaust fan at the top of the Oro Hondo Shaft. The fan had not been operated since about 2001, but a team of electricians and mechanics had the fan running in just six hours. The surface crew also shut down an exhaust fan in nearby Kirk Canyon.
The change in ventilation was dramatic, especially at the 4550 Level, where humidity had been near 100 percent. Now the humidity is about 80 percent. "This was a huge improvement in working conditions," Sanford Lab Engineering Director Todd Seaman said. "It also saves us a lot of money." Sanford Lab engineers had considered adding cooling units -- large, expensive underground air conditioners. Now those units will not be necessary until underground laboratories are built.
Ventilation Technician LeEtta Shaffner and Ventilation Engineer Bryce Pietzyk led the team that changed the airflow. Shaffner had previously worked at the Homestake gold mine. "Her experience here helped us create a modified version of what they had before," Seaman said. The team also worked with former Homestake ventilation engineer John Marks, who frequently consults on Sanford Lab projects. After running computer models, the one team headed underground with sledgehammers while another team refurbished the Oro Hondo fan.
"We challenged them to come up with something, and they responded," Seaman said.
Ron Wheeler, executive director of the South Dakota Science and Technology Authority, said opening the 3500 Level was part of a larger plan to better ventilate Homestake's lower levels.  "Fortunately, more than 80 percent of our technicians and engineers are former Homestake employees," Wheeler said. "Some of them have 30-plus years of experience underground. They know how this gold mine worked, and their experience is helping us reopen Homestake safely and quickly."
The South Dakota Science and Technology Authority is reopening the former Homestake gold mine to the 4,850-foot level, where sensitive experiments will be protected from cosmic radiation. The National Science Foundation is considering an even larger proposal to convert the Sanford Lab into a national Deep Underground Science and Engineering Laboratory. The DUSEL would have campuses from the surface down to the deepest level of the mine, 8,000 feet underground.
Homestake had been slowly filing with water since 2003. Now the SDSTA is pumping water out. This week the water level is just below the 4,700-foot level, down 170 feet from the high-water mark set last August. The 4850 Level, where the first major physics experiments will be installed, will be dry by spring or early summer.