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NEAR ENNIS - A helicopter dropped geologists and engineers on top of a cliff near the Madison Dam on Tuesday to inspect the cliff and determine if it is safe for crews repairing the dam.

The handful of engineers and geologists are from NTL in Great Falls. Along with PPL officials, they are inspecting the rocks to determine if they need to be anchored to prevent a boulder from falling on the dam again in the future.

While a final decision isn't expected until later today, based on what they have seen, officials who inspected the rocks today say they feel they will have to anchor the rock. The anchoring process would include drilling hole in the rock and inserting a rod into it to prevent the rock from breaking up.

The crew is expected to make a determination on whether to brace the cliff and will decide what measures need to be taken to prevent a boulder from falling into the dam in the future.

At the same time, temporary patch work will begin on the dam either today or Wednesday. If the patch holds, crews will raise lake three feet then will put in a more permanent, temporary dam.

Crews don't plan to work on the dam until the rocks are anchored. It is expected to be a couple weeks before they begin anchoring the rocks.

PPL Montana officials hope that repair work can start Wednesday with large 3,000-pound bags of concrete dropped around the rock to plug the gaps in the dam. The bags will be used to slow the flow of water.

If the temporary patch works then the Ennis Lake level will be raised back up to its normal winter operating level. They hope to have the patch installed either on Tuesday or Wednesday.

The geologists will also try to determine if there is any future danger to the dam and will offer advice about what, if anything, PPL will need to do to stabilize the cliff above the dam, according to PPL Montana officials.

PPL plans to have the dam repaired completely by end of year.

On Monday, Aug. 30, a huge rock, measuring half the size of a house, fell from the cliff over the dam, crashing into the west side of the dam. The rock crushed one end of the dam and damaged at least two of the hydraulically operated gates releasing water from the lake.

Booms were deployed in the Madison River to capture a small amount of oil - about 15 to 20 gallons - that spilled into the Madison River when the boulder severed a hydraulic line. No additional oil is leaking into the river. Flashboards were also damaged as a result of the falling boulder.

Madison Dam is a four-unit hydroelectric plant on the Madison River at the head of Bear Trap Canyon, about 10 miles north of Ennis.