Update Friday, September 23:
Recreation on the Huron River has been resumed and, so far, water tests show no threat to human health, according to an updated press release by the city of Ann Arbor.
It is believed that the leak was caused after a motorist drove through barriers near the entrance to Gallup Park. The investigation of that incident is ongoing.
Raw sewage flowed out of the pipe from Saturday, September 17 to Monday, September 19.
More from the city’s press release:
The Huron River was flowing at approximately 170 cubic feet per second on Sept. 20, equivalent to 110 million gallons per day. Therefore, a 600,000 gallon discharge over 36 hours would constitute less than half a percent of the flow of the river. City staff and the Washtenaw County Health Department continue to monitor the river for bacteria; tests have, so far, indicated no threat to human health.
The city says it hopes to improve its response to events like this in the future by implementing “enhanced training regarding construction site release protocols.”
Ann Arbor officials estimate about 600,000 gallons of sewage leaked into the Huron River.
The leak — caused by construction debris accumulating in a sanitary sewer — blocked flow sometime between Saturday afternoon and Monday morning, when the blockage was discovered and flow was restored.
More from the city's press release:
There are no communities downstream of the plant that withdraws water from the Huron River for drinking purposes. In accordance with regulatory protocols, City of Ann Arbor staff contacted the Michigan Department of Environmental Quality to inform them of this unfortunate incident.
According to Ryan Stanton of the Ann Arbor News, Ann Arbor officials confirmed the blockage was construction related.
"It is always our intent to be protective of our natural environment," City Administrator Howard Lazarus said at Monday's city council meeting. "When something like this occurs, we all feel that we have let the public down in protecting our natural resources, and we will be ever more diligent in making sure that, to the best of our abilities, it does not occur again."
Sewage has leaked into the Huron River and its tributaries multiple times in the past year. In May, 36,000 gallons of sewage leaked into the Huron River near Bird Hills Park. In April, 400,000 gallons overflowed into Malletts Creek.
Paddling and canoe trips are suspended on Geddes Pond, and Argo-Gallup canoe trips are suspended until water test results are in.
Users can see updated information here.
Michigan Radio reached out to the city of Ann Arbor for comment. Spokesman Robert Kellar responded, "we are currently putting together data and information for city council on the event. As soon as that is done we will be happy to answer your questions."