Concrete slurry washed into Mill Creek on Thursday from the Interstate-215 reconstruction site, killing trout downstream and sickening dogs while turning the creek water white for a time.
The spill was first reported Thursday at 4:30 p.m. by a resident who witnessed a “concrete free flow slurry mix” pouring into the creek while he was walking along Mill Creek Canyon Road, below the freeway, according to a report posted on Utah Department of Environmental Quality’s (DEQ) spill database.
Officials said they have yet to determine how much material spilled into Mill Creek, which passes by yards of Salt Lake County homes along much of its path to the Jordan River.
The Utah Department of Transportation, which is overseeing the freeway reconstruction, was onsite near Skyline High School, assisting in the cleanup and investigating what went wrong.
UDOT spokesman John Gleason said people should steer clear of the creek for its entire run below the freeway.
“It has caused increased pH [levels in the creek], which causes skin irritation,” Gleason said. “Our top priority is to get the word out for people and pets to stay away from the creek. We are still determining how this material was spilled. We are anticipating that next week it should be cleaned up.”
Ralph L. Wadsworth Construction, the contractor on the freeway project, referred press queries to its Texas-based parent Sterling Construction, which did not respond to The Tribune’s request for comment conveyed by Wadsworth staff.
The upstream stretch of Mill Creek, which drains one of Salt Lake County’s most popular outdoor destinations, was not affected by the spill. Downstream was a different picture, with large trout floating belly up for at least 2 miles to 2000 East, according to the Utah Division of Wildlife Resources. The bed of the creek remained discolored on Friday.
The agency stocks Mill Creek with native Bonneville cutthroat and estimates it holds about 500 catchable fish, including nonnative brown trout, per mile, according to spokeswoman Faith Heaton Jolley.
“We have heard reports, but we haven’t yet confirmed any fish kills below 2000 East,” she said. ”The fish can’t tolerate any significant changes in pH level, especially when it happens that quickly. It didn’t help there’s lower water this year and it’s warmer because of drought. That was another stressor on top of those previous stressors.”
The DEQ spill report said the source of the spill has been stopped, but officials have yet to determine how much material got into the creek. The report did indicate what triggered the spill.
“Concrete was released from a catch basin that was part of a freeway construction project, due to a failure to block an inlet when they were filling the basin,” the report said. “Storm drains that were no longer needed were being filled up with concrete and the storm drain outflows were not blocked, which allowed the concrete to flow into Mill Creek.”
Once the creek is deemed safe, DWR intends to restock it with cutthroat trout.