The U.S. Army Corps of Engineers this week advertised for bids to insert a second diaphragm wall into the earthen section of Wolf Creek Dam.

Steve Foshee, public affairs office for the Corps, said bids will be opened March 11and hopefully a contract can be let by late May. Repairs to the mile-long dam, considered in high risk of failure, are expected to take up to seven years.

The new diaphragm wall will be upstream from a similar wall put in the dam during the 1970s. The new wall will be longer and deeper than the original wall installed after more serious leaks were discovered in the late 1960s. An Italian firm, ISO Corporation, inserted the original diaphragm wall.

David Hendrix, project manager at the U.S. Army Corps of Engineers’ Nashville District Office said specifications of the new wall will have a minimum requirement of at least two feet thick. Its depth in the bedrock will range to more than 100 feet, depending on the formation of the rock.

“We’re taking the wall down to the Catheys Formation,” said Hendrix. He explained that this is more competent limestone rock that the Leipers Formation, a karst limestone region beneath the dam that is marked by sinkholes and interspersed with abrupt ridges, irregular, bulging rocks, caverns and underground streams. Seepage through this karst causes the dam to develop serious leaks.

Hendrix said the diaphragm wall, part of a $309 million rehabilitation of the dam, can be installed a couple of ways. One is what he called a secant pile wall, formed by drilling large holes adjacent to one another. Another method is a panel wall, formed by using a mill to excavate rectangular openings in which the wall would be poured in short concrete panels with joints between each section.

The new concrete wall will start immediately upstream of the right most concrete monoliths and run the length of the embankment into the right abutment some 1,650 feet beyond the existing wall. It will be constructed to a depth as much as 75 feet below the majority of the original wall, according to the Corps’ description of the project.

Foshee said requests for proposals to insert the diaphragm were issued Monday on the Internet and with mailings. He said seven firms, mostly outside the United States, have expressed interest in the project.

Wolf Creek Dam is 5,736 feet long with a maximum height of 258 feet. The earthen section of the dam is 3,940 feet long and the remaining 1,796 feet are concrete. The most serious leaks were in the area where the earthen section of the dam joins the concrete section.

Lake Cumberland is 56 years old. Gates were closed and water started filling the 101-mile-long lake in December 1951. The level of the lake was lowered 43 feet last January to ease pressure on the dam.