Details released for Homestake Mine re-entry, dewatering program

BY WENDY PITLICK, Black Hills Pioneer
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LEAD - By the time the water in the Homestake Mine rises to the 5,000-foot level this September, officials hope to have it contained.

Water enters the old mine at an estimated 700 gallons a minute, officials from the mine said, and they're not sure when in September the 5,000-foot alarm will go off. Before it does, they hope to have a pumping system in place capable of keeping the water at the 5,300-foot level. This would allow crew to safely begin rehabilitating the mine's shafts and tunnels to make way for a planned "interim" lab at the 4,850-foot level.

All that work started Feb. 8 and is scheduled to be completed by Sept. 11, 2007. "This is a very tight timeframe and we're going to have to move expeditiously to make it happen," said Dave Snyder, executive director of the South Dakota Science and Technology Authority. "My objective in guiding this process is that we only do what is necessary to arrest the water."

The Homestake Mine Re-Entry and Dewatering Program was unveiled and approved Wednesday during the lab authority's regular board meeting. The plan was developed by Short, Elliott and Hendrickson (SEH) Inc. of St. Paul, Minn., who worked with representatives from the authority including Dave Snyder and Greg King, the original engineering firm Dynatec Corporation, Homestake principal investigator Dr. Kevin Lesko, Homestake consultants and experts Gary Lillehaug, John Marks and Tom Regan along with numerous other engineering and science consultants.

Overall, the plan will cost $7 million, with $2 million allocated toward up-front surface work and equipment purchases that will happen within the next couple of months. According to Snyder, those portions of the plan, which qualify for HUD funds, will be funded out of a $10 million grant approved in 2003.

Plan priorities

In establishing the dewatering and re-entry plan, Chuck Michael of SEH Inc. said the priorities include personnel safety, reliability and quality of the systems and processes. Michael also said the plan's priorities include using the lowest initial and operating costs, making sure the plan is compatible with the authority's Early Implementation Plan to put science in the 4,850-foot level, and to make sure the plan is compatible with the Deep Underground Science and Engineering Lab.

In keeping with these priorities, Michael said highlights of the plan include only rehabilitating the Ross Shaft. While a 2004 proposal by Dynatec Corporation originally called for the authority to rehabilitate both the Yates and the Ross Shafts, Michael explained that to do that would be too costly, as the initial thrust of the project is just to pump water out of the mine. Both primary and secondary entrance and exit functions can be managed through the Ross Shaft using personnel hoists and production hoists so workers will always have more than one way to get out. To rehabilitate both shafts, he said would double the cost and would not be necessary, since mine access is not the initial priority. Yates Shaft rehabilitation, he said would be better done when science is put into the mine. Once that is complete, Michael said the plan would be to use the Yates Shaft as a personnel hoist, and the Ross Shaft as an equipment hoist. But to do that, he said will take more money than the authority has for the initial preparation and dewatering of the mine.

In addition to the shaft rehabilitation, Michael explained right away that the objective for dewatering will be to contain water in the mine at 5,300 feet. While the Early Implementation Plan only calls for experiments to be done as low as 4,850 feet, Michael said the extra 450 feet of dry land will allow for mechanical failures and power outages. "If that happens ... we're not holding the water just an inch below our feet," Michael said.

Preliminary expenses

But before anyone can re-enter the mine to do anything, Michael said there will be up-front costs to purchase safety equipment, mobilize and demobilize contractors and equipment, conduct detailed engineering, and get permits for water treatment and other work. Preliminary expenses for opening up the Ross Shaft and dewatering the mine will include $387,000 for mobilization, $31,000 for demobilization, and $278,000 for detailed engineering reports and permitting costs.

Michael said it will also be necessary to re-establish power to the mine, re-constitute the water treatment facility, and re-commission the Ross Hoist. Overall, Michael said this price tag is estimated to come in at $951,000.

The Ross Shaft

Refurbishing the Ross Shaft will be a significant part of the $967,329 project cost, Michael said. The plan calls for all new electrical work, including the power supply cables, motors, starters, and fiber optics, which will allow for a more efficient operating system. It also calls for the authority to completely refurbish the 700 horsepower pumps in the shaft, and put a new submersible pump at 5,300 feet. With all of this equipment, Michael said the Ross Shaft would be solely dedicated to driving the hoists and the pumps. If the National Science Foundation ultimately chooses the Homestake Mine for the DUSEL, Michael said then the authority can still go back into the mine and power up the remaining four pumps to dewater the rest of the mine at 7,400 feet.

Ross Shaft rehabilitation includes $412,206 just to open the shaft, $263,991 for rehabilitation work, and $156,214 for underground equipment. The remaining $134,000 will be for ventilation, rehabilitation for the 4,850-foot level, and dewatering the bulkheads, which limit ventilation air flow to the Ross.

These costs don't include the estimated $1,330,170 for electrical systems in the Ross, which are also included in the plan.

"The thrust right now is to dewater the mine," Michael said. "It isn't necessarily to occupy the mine. When we get people into the mine we will look at it differently."

While the authority board liked the idea of saving money by only rehabilitating one shaft for pumping, some expressed concern that operating only one shaft could cause a safety concern. However, King, who was involved with cleanup and reclamation work when the mine shut down 2002 said the levels of the mine aren't all tied to both the Yates and the Ross, so if there was a failure in one of the shafts laborers wouldn't necessarily be able to get out via the other shaft. Further, he said Ross Shaft rehabilitation will be done from the top down, so laborers will always know what is above them.

"As we re-enter everything above us is going to be checked, bolted and the likelihood of a collapse above where the men are working is very rare," King said.

Further, Michael explained that the re-entry program calls for the authority to purchase two, four-person refuge chambers that will be good for 48-hours and portable so laborers can haul them throughout the mine. Those crews working the pumps would have one chamber, while investigation crews will have another. Additionally, he said each person in the mine will be required to carry two one-hour self contained breathing apparatus units that can be used in the event that the shaft fails somehow.

Sending a team into the mine

Before any work can happen inside the mine, King explained that a subcommittee will examine Homestake's old cleanup closure records and maps, to identify potential areas of risk in order to make a level-by-level plan. Everyone on the committee, King said, will have been involved with Homestake's initial cleanup efforts, and will have a good, working knowledge of exactly what is inside the mine.

The team, King said will consist of four members. In addition to the hoist operator and the top attenders, the team will include a shaft person who will be available at the station for communication purposes, and three people in the various mine levels doing air sampling and ground condition checks. The third person will do documentation and act as the safety officer. Additionally, King said the crews will also conduct some earth science inspections in an effort to accommodate potential science in the mine.

"We don't expect to go into every level in every place," Michael said. "But we have to make sure we can get to the 4,850 and do that safely. I think we have thought about all of the risk that we need to assess and manage, and ways to do that quickly."

Mine ventilation

While the Oro Hondo ventilation system is the existing means of airflow through the Homestake Mine, Michael said the cost to rehabilitate and operate the system would be extensive. In order to cut costs, he explained that it would be less expensive - and just as effective - to modify the No. 5 Shaft for main ventilation to the Ross Shaft and limited ventilation to the Yates. That is compared to the Oro Hondo, which provides unnecessary ventilation throughout the entire mine.

DeWatering the Mine

Once all the surface work has been completed the process for re-entry and dewatering will begin. The total cost for installing the shaft pumps and maintaining its services in the Ross will be at $394,000. This includes rebuilding three of the mine's existing pumps and purchasing a new submersible pump for the 5,300-foot level. Under the dewatering plan, water will be drawn out of the mine from the top down, using storage sumps and pumps, in an effort to minimize temperature differences for water treatment. The existing sump at 1,250 will draw water from the 2,450-foot level, and an existing sump at 2,450 will draw water from 3,650. Pumping will continue like that through the 3,650 and 5,000-foot levels with the sumps ultimately drawing water from the new submersible pump at the 5,300 foot level.

Once it is pumped out of the mine, Michael said the water will run out to the water treatment plant, where it will be treated for temperature and sand. Government regulations call for all water to be cooled to at least 65 degrees before it can be disposed, so with some water temperatures possibly reaching up to 85 degrees, treatment will be necessary. Once treated, the water will be deposited into Gold Run Creek.

Re-entry schedule

Because the water levels in the mine are rapidly rising, and the timeline for the DUSEL announcement is fast approaching, all of this work must be completed immediately, Michael said. Crews started working on mobilization Thursday, and will be finished by Feb. 14. The very next day a detailed schedule calls for laborers to begin re-commissioning the Ross Hoist, with work to be completed by March 7.

Crews will start opening the Ross Shaft on March 6, and will work for four months until the shaft opens on July 5. During this time, contractors will work on the electrical system in the Ross from June 28 through Aug. 23. Rehabilitation of the Ross will begin July 6, and will also continue until Aug. 23. Then, the final step to install the shaft pumps will begin Aug. 24, and continue through to Sept. 11.

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