This week’s heavy rainfall caused cement grout from a road project to wash into Robbinsdale’s Lower Twin Lake, alarming some lake residents.

Residents reported the spill to the city after seeing the cloudy liquid fan out into the lake from a storm sewer.

“It clearly was a huge plume,” said Wendy Wersal, president of the lake’s homeowners association. “We’re concerned about it.”

The city said the foam concrete was from a project to repair a waterline on County Road 9 that passes through Robbinsdale — the third time the suburb has been affected by a waterline that doesn’t even serve the city.

Instead, it carries water from Minneapolis to a Crystal reservoir to provide water to homes and businesses in Crystal, New Hope and Golden Valley.

The 2-mile waterline passes through Robbinsdale, where it burst twice in just over a year’s time in 2013 and 2014, flooding streets and nearby homes and creating a massive 20-foot-deep sinkhole.

The Joint Water Commission, which includes leaders from Crystal, New Hope and Golden Valley, oversees the water main project.

“It will be nice when the project is done,” said Marcia Glick, Robbinsdale’s city manager.

Rain blamed

This summer, crews started work on fixing the waterline, lining the old pipe with new pipes. But heavy rainfall this week caused cellular grout used between the two pipes to wash away into the stormwater sewer system, Glick said.

The spill is unrelated to nearby road reconstruction work also being done on County Road 9 by Hennepin County.

Glick said the city’s storm sewer usually collects debris and grit before water is discharged into the lake, but the grout was too thin and fine, seeping into water that washed into Lower Twin Lake, home to about two dozen residents.

The Minnesota Pollution Control Agency is now working with the city, sending a stormwater expert out Wednesday to review the spill, MPCA spokesman Sam Brungardt said, but at this point, it doesn’t appear to be serious.

“It will not have a lasting impact on water quality or wildlife or residents,” he said. “It probably looks worse than it is.”