On Monday, the second phase of the Hofmann Dam removal project – the regrading of Swan Pond Park – officially started although much of the goings-on there were strictly preliminary.
Meanwhile, back at the dam, it looked as if work was winding down. The center 150 feet of the dam has been removed to bedrock. But with the Hofmann Dam notched, work crews will again turn their attention to the remains of the horseshoe dam, still intact several yards behind Hofmann.
While some demolition of that “legacy” dam occurred in late June, the Army Corps of Engineers has now asked Illinois Constructors Corporation to remove the rest of the dam, which has turned out to be quite a substantial structure, according to Jeff Zuercher, a project manager for the Army Corps.
As much as 7 feet of the legacy dam’s face remains standing, said Zuercher, and will “need to be removed down to [the level] we removed the Hofmann Dam to.” The water level just above the legacy dam is clearly higher than the bedrock level where the Hofmann Dam used to be.
The Army Corps on Monday delivered a plan to remove the legacy dam to Illinois Constructors Corporation, Zuercher said, and is awaiting the contractor’s response.
The plan would be to remove the entire legacy dam, “then regrade the area so there’s a smooth transition between the two areas,” said Zuercher. “There’s a lot of rock debris and sediment behind the legacy dam that will be removed and disposed of.”
According to Zuercher, an excavator will scoop out toxic sediment from behind the dam and place it in a roll-off box that will likely be located on the access road built on the south bank of the river. The sediment will be de-watered and removed from the site. Zuercher was not sure exactly how much sediment will have to be removed behind the legacy dam.
“We’re trying to get a good handle on that,” Zuercher said.
As for how much the removal of the legacy dam will drop water levels behind it, Zuercher said he didn’t have firm figures.
“We know it’s holding back some water, but it’s hard to say how much,” Zuercher said. “It’s possibly going to drop some. How far upstream that goes, I don’t know right now.”
Over in Swan Pond Park on Monday morning, crews from Illinois Constructors Corporation were putting up orange plastic hurricane fencing around trees and other sections of the park that will be off limits to the heavy equipment during the regarding operation.
The entire work area will be off limits during construction and a chain-link fence is expected to go up around Swan Pond Park this week.
Two ComEd trucks were parked on Burling Road, adjacent to Swan Pond Park on Monday in anticipation of work to reroute underground power lines there. Because of the regrading work, the power lines will have to be buried much deeper than they are now.
The earth-moving and tree-removal operation in other areas of Swan Pond Park may begin while ComEd works on the power line issue, said Zuercher. Trees, including many large, mature specimens slated for removal, have been tagged with yellow ribbons.