The removal of Hofmann Dam, which was scheduled to begin on Monday, will commence Wednesday morning when a 30-foot hole is punched through its concrete face.
The Riverside village board gave the green light to move ahead with the work at a special meeting held June 11. At that time, Jeff Zuercher, project manager for the U.S. Army Corps of Engineers, had announced that work was slated to proceed on June 18.
The reason for the delay, Zuercher said, was that the contractor for the job temporarily needed the excavator, to be used for the Hofmann notching, at another job site.
On Monday, the village of Riverside provided an itinerary for the dam removal, setting Wednesday as the start date. According to Zuercher, an excavator outfitted with a jackhammer will begin chipping away at the center of the dam.
“They’ll begin about [7:15] and go all day to get the notch,” said Zuercher.
An air compressor set up near the Hofmann Tower, which has been cordoned off by construction fencing, will be attached to the jackhammer on the 20-to 30-foot-long excavator.
“The excavator will extend the arm and start to pound away at the dam,” said Zuercher. “As the hammer pokes away, pieces will break out, and it will keep chipping away.”
After the first day, Zuercher said he expects the notch to be 30-feet wide by about 5-feet deep. The next day, the excavator will take the 30-foot notch down to bedrock. By Monday, June 25 the water behind the dam should have equalized with the water downstream.
If there are no work interruptions due to weather or other factors, the entire 150-foot-wide notch in the dam should be complete in 10 more working days, by July 7. According to Zuercher, the entire removal will be done by the jackhammer method, similar to the way Fairbank Dam was removed earlier this year.
The water level of the Des Plaines River inched up over the weekend after a soaking rain Saturday night and Sunday morning. The water level, which had dipped to just below 2 feet had risen to nearly 3 feet by Sunday afternoon.
By Tuesday morning, the water level had dipped back to 2 feet.
Even before the dam is completely removed, according to the construction itinerary, planting of the exposed mud flats above the dam will begin. That work is slated to begin June 29 and continue until almost the end of July.
The gravel access roads to the dam removal site should be removed by the end of July and the turbidity curtain, which is topped with yellow plastic and marks the extent of the sediment stabilization upstream of the dam, is scheduled to come out of the river by Aug. 7.