Published: September 29, 2007 11:23 pm      

Corps: Wolf Creek Dam repair going as scheduled

A U.S. Army Corps of Engineers’ official said last week that grouting to stop leaks in Wolf Creek Dam is moving along as scheduled and advertisements likely will be published late in October for a contractor to insert a second concrete diaphragm wall into the earthen part of the structure.

Dave Hendrix, project manager for the $309 million dam rehabilitation, gave the information ahead of an announcement by Congressman Hal Rogers that the Corps will raise the lake up to 10 feet above current levels in advance of next summer’s tourist season. Rogers said the Corps’ decision “comes as structural repairs on Wolf Creek Dam are on track to support incrementally higher water levels.”

Hendrix said potential bidders on the diaphragm will be given 90 days to prepare proposals and a contract probably will be let in March. This is two to three months later than the December-January period previously mentioned by the Corps. It is expected to take up to seven years to complete the project.

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.

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 original wall was inserted in the dam between 1975 and 1979 after leaks apparently more serious than now were discovered in 1968. At least two sinkholes developed in the vicinity of the power grid below the dam and muddy water was observed in the tailrace.

Sinkholes would be taken more seriously now. Lieutenant Colonel (LTC) Steven Roemhildt, former commander of the Corps’ Nashville District, told the Commonwealth Journal this past summer that if sinkholes were to develop in the dam, the area along the Cumberland River below the dam would be evacuated.

The Corps has insisted all along the current seepage problem, observed early in 2005 and announced in August of that year, is not as serious as the 1968 event. However, a report by an outside group of experts said the dam, if not repaired, could fail within five years.

A roller compacted concrete dam, essentially to replace the earthen section of the existing dam, was considered and evaluated. However, Hendrix said this new type of dam is no longer an option. Engineers have said the concrete diaphragm wall will extend about 100 feet into the bedrock, deep enough to get beneath the porous limestone karst through which water is seeping.

Grouting — pumping liquid concrete into the dam — has been under way since January. Grouting is credited with saving the dam in the late 1960s and is being used again to plug cavities in the limestone rock prior to insertion of another diaphragm wall. Chemicals are added to the grout to make the soupy mixture seek and fill the empty spaces.

As of September 19, all 50 drilled holes in the gallery have been grouted. Hendrix said the critical area where the earthen part of the dam joins the concrete section has been grouted and contractors have moved to what he called Critical Area No. 2 at the end of the original wall farthest from the concrete section. At this point, a total of more than 126,605 gallons of grout have been pumped into the foundation.

“We haven’t found anything we didn’t know was there,” said Hendrix. He said the grouting is effective and the dam is safer every day.

Much more information has been released to the public about the current problem than during the late 1960s and 1970s. The Corps, time and time again, has taken reporters into the gallery in the bowels of the dam and along the earthen embankment to point out the seepage areas and methods of repair.

Emphasizing that safety is a top priority, the Corps in January this year announced that the lake would be lowered some 43 feet — 680 feet above sea level — to relieve pressure on the ailing dam. Late in July, the Corps revealed that the 680 foot level would be maintained throughout 2008. Then came the announcement late last week by Congressman Rogers that the level may be raised up to 10 feet by next summer.

The Corps has been hard pressed to maintain the current level because of an extreme drought in the Cumberland River Basin. Additional water is being released from Laurel River Lake to keep Lake Cumberland high enough so John Sherman Cooper Power Station at Burnside can continue to operate. The power plant uses water from the lake to cool its generators.

As of Saturday, the lake was 679.15 above sea level and steady. Discharge of water from Wolf Creek Dam is being reduced, according to the Corps’ website.