School bus-sized boulder damages Madison Dam sted: Tuesday, August 31, 2010 12:15 am
By LAUREN RUSSELL, Chronicle Staff Writer | 0 comments
PPL Montana employees are working to contain damage to the Madison Dam near Ennis caused when a school bus-sized boulder dislodged and smashed into the western crest of the dam early Monday morning.
There were no injuries and the hydroelectric plant was still producing electricity at full capacity as of Monday afternoon, said David Hoffman, spokesman for PPL. Damages included a severed hydraulic line that produced a small oil spill.
The power company is planning an emergency drawdown of Ennis Lake to identify total damage to the dam and relieve water pressure, but how this will be done is still being discussed, Hoffman said.
"We do have to bring Ennis Lake 9 feet down," Hoffman said. "We're still discussing the best way to do that-slowly or quickly."
The damage occurred at about 3:20 a.m., when the large boulder dislodged from the steep cliff on the west side of the dam. The impact put a 30-foot-wide crater into the dam, and the boulder is still jammed against the dam.
An on-call PPL employee was alerted to the collapse by an alarm, Hoffman said.
Water is leaking around the edges of the boulder, which is causing river flows downstream of the Madison Dam to run at about 2,000 cubic feet per second, which is about 500 cfs more than usual, Hoffman said.
Flow rates are not expected to surpass 2,000 cfs, and flooding is not anticipated at this point, he said.
The falling boulder severed a line that operates several of the dam's spill gates and caused about 12 to 15 gallons of oil to leak into the Madison River, Hoffman said.
Hoffman said the broken line is no longer leaking oil, and a combination of absorbent and booms are being used to capture the oil in the river. Hoffman said the booms will probably be removed by the end of the day Monday.
"There is no indication that there has been any fish kill," or obvious harm to wildlife due to the oil, he said.
Hoffman said PPL has called in additional staff to determine a plan for repairing the dam and removing the boulder. A decision on how to conduct the drawdown of Ennis Lake will be made within the next day or so. The drawdown and repairs will take at least several weeks; there's no firm timetable yet, he said.
"It's probably going to be a while," Hoffman said.
The Madison County Sheriff's Department has closed the Trail Creek Trailhead area until further notice. Sheriff Dave Schenk said that "possible hazardous conditions" below the dam necessitated the closure, which will be enforced by PPL.
Andrea Jones, spokeswoman for Montana Fish, Wildlife and Parks' Region 3 office, said officials didn't have enough information to comment on possible effects of the lake drawdown or the oil spill Monday afternoon.
"We don't know enough about the situation at this time to say anything about potential fish resource effects," she said.
School bus-sized boulder damages Madison Dam - The Bozeman Daily Chronicle: News