Posted on January 18, 2023
Construction crews have removed about 3,000 cubic yards of material from Capitol Lake as a part of a $3.5 million project to plug an existing well and improve water quality in the iconic lake.
Of those funds, $500,000 is coming from the state’s General Fund and $3 million in federal funds coming from the American Rescue Plan Act.
Fort Pierre-based Morris Inc. is the contractor overseeing the dredging portion of the project.
“The material being removed from Capitol Lake primarily consists of sediment which has flowed down Capitol Creek for more than 100 years,” Leah Haugan, special projects coordinator with the state Bureau of Administration, said. “The material consists primarily of silt and clay size particles which have been eroded from the hills surrounding Hilger’s Gulch. A small percentage of the material has been found to be sand, likely derived from many years of application to the surrounding roads. A significant percentage is also derived from the waterfowl population which is present in the lake, particularly in the winter months.”
The construction equipment involved consists of a terrestrial excavator for loading material from barges into the transport trucks, two hopper barges for hauling material from the dredging location to the loading area, an amphibious excavator for dredging the lake bed, a push boat to move the hopper barges and a long reach excavator, Haugan said.
December’s winter storms and extreme cold temperatures were a challenge for construction crews, who were able to clear the site of ice and snow allowing the construction schedule to proceed as planned.
At most, Morris has around six workers on site in addition to three to five trucks hauling material to a dump site location.
Visitors to Capitol Lake are still able to access the Veterans Memorials and may notice a floating silt curtain surrounding the dock near the fountain.
“This is keeping the dredged material away from our siphon; which ensures our siphon system is diverting the cleanest water possible around the lake,” Haugan said.
The lake’s warmer temperatures also lessen the need for ice removal, though crews typically have to remove a thin layer of ice to resume dredging operations every day.
In addition to sediment, Haugan said crews have recovered an abandoned coax type cable, a tire and small amounts of plastic and trash from the lake.
Brian Walsh, public affairs director with the state Department of Agriculture and Natural Resources, said the lake’s water quality will remain in post-dredge condition for some time to come.
Plugging the well will have a major impact on the water quality, Walsh added.
“The well water quality dominates the lake water quality and has high levels of several ions such as sulfates, chlorides, and sodium, and metals such as iron and manganese,” Walsh said. “The water quality of the lake will not change dramatically following the dredging, but once the well is plugged, the lake water quality will mimic the runoff currently occurring from the watershed.”
According to the Office of the State Engineer, visitors to the lake can expect to see snapping turtles and waterfowl, but the large carp will no longer be present in the lake.
