City project was the source of cloudy water in Vermillion
Dewatering work being done to allow the reconstruction of Walnut Street has been identified as the cause of cloudy water discovered earlier this summer in the Vermillion River.
The Minnesota Pollution Control Agency issued the city of Farmington a Notice of Violation for nuisance conditions related to the discharge, which caused white clouds to form in an inlet in the Kuchera entrance of Rambling River Park. There is no fine related to the violation, which did not impact water quality, and the dewatering for the Walnut Street project is completed.
Chelsea Domeier, industrial wastewater inspector for the MPCA, said nothing in the city's dewatering plan was out of the ordinary.
Dewatering involves pumping groundwater out of an area to lower the water table in an area. In this case, the dewatering was necessary to allow the installation of utilities along Walnut Street.
Figuring out exactly what caused the murky water took some time. MPCA inspectors sampled water in the cloudy area and water both upstream and downstream in the Vermillion. They eventually traced the water back to Walnut.
Domeier said it appears calcium and magnesium settled out of the pumped-out groundwater as it flowed to the Vermillion, then dissolved again once it hit the river. Slow-motion video shows tiny white fingers dissipating as they stretched from the inlet, where the cloudiness was most pronounced, out into the main body of the river.
"You're seeing kind of that build up of white because the flow in the Vermillion River was a lot higher than the flow coming out of the storm sewer," Domeier said. "It's kind of getting stuck out there."
Water from Walnut Street discharged through a separate pipeline farther downriver did not cause any cloudiness. Domeier said it's possible there was a chemical reaction of some kind along the way.
"It's really just a chemical reaction that was taking place," Domeier said. "Maybe it was reacting to the concrete in the storm sewer. It really isn't anything that could have been prevented."
Domeier said the MPCA would work with the city on future dewatering projects to make sure there are not similar problems. For now, she's happy to have a mystery solved.
"It had a good outcome knowing it wasn't anything that was an environmental concern," Domeier said.