The city dumped an estimated 2 million gallons of untreated sewage into the Flint River Sunday, Aug. 18, just months after officials warned wastewater infrastructure was fast approaching a “critical point.”

A partial report filed by the city with the state Department of Environment, Great Lakes and Energy on Tuesday, Aug. 20, says a “flash flood event” overflowed primary settling tanks at the city’s wastewater treatment plant on Beecher Road, sending raw waste onto the ground and into a storm sewer drain that discharges directly to the river.

Although the city announced the spill three days ago, it did not reveal the volume of the discharge until filing the partial report with EGLE, and has yet to indicate what actions it took to minimize impact from the discharge or what plans is has to prevent a similar spill in the future.

An advisory issued Sunday, warning people to avoid contact with the river because of potentially high bacteria levels related to the spill, remained in effect on Wednesday, Aug. 21.

Flint’s wastewater treatment plant complex includes 10 outdoor settling tanks similar to massive swimming pools that hold millions of gallons of sewage. The tanks are used to remove solid material from wastewater before it is moved to a clarifying tank for further treatment before finally being discharged to the river.

Sunday’s sewage spill comes just months after City Council approved nearly $1 million in contracts with companies to help design upgrades to sewage treatment infrastructure after officials warned that the existing system was at risk of “catastrophic failure.”

The city is seeking a $34 million state sewer revolving loan to fund the improvements on its wish list.

“We’re going to get to a point where we can’t treat our wastewater and sewage anymore,” Bincsik said at the time . “We won’t have to talk about drinking water anymore, because we’ll talk about nothing but the raw sewage that gets discharged into the Flint River.”

The city treats about 50 million gallons of wastewater daily.

National Weather Service meteorologist Alex Manion said heavy rains swept through parts of Genesee County, including Flint, last weekend.

Bishop Airport measured more than 2.2 inches of rain in a three-hour period starting late on Saturday, Aug. 17, and continuing to early Sunday.

Flint’s report to the state says its spill occurred from 2-3 a.m. Sunday.

MLive-The Flint Journal could not immediately reach a Flint spokeswoman for further comment on Sunday’s sewage spill, but on Flint’s website, officials say they have the capacity to hold about 20 million gallons of the excess water temporarily in a large storage basin in cases of heavy rain.

Once the tank is full, the excess flows are typically discharged to the river but only after water has been allowed to settle and and has been “disinfected with a bleach solution,” the website says.

The city’s report to the state does not mention the retention basin and says Sunday’s release was “raw sewage.”

Earlier this year, the city sought a waiver from the Genesee County Health Department, requesting that it be allowed to skip testing river water for bacteria after sewage spills in cases in which the discharge comes from its retention basin.

“(Sewage discharges are) actually ‘cleaner’ than the river water, so it’s impact on the river is positive, if anything,” Robert Case, Flint’s water pollution control division manager, said in an email to MLive-The Flint Journal in June, about a month after the waiver request was denied.