Heavy rains last week caused roughly 11 million gallons of sewage and storm water to pour into the Grand and Red Cedar rivers.

More than 10 million gallons poured into the Grand River and roughly 470,000 gallons into the Red Cedar River. A public access point on the Grand near Moore’s Park was potentially affected by the overflow, the city said.

That’s on top of 25 million gallons of sewage and storm water that went into the Grand River and 1.9 million and went into the Red Cedar River after more than 2 inches of rain from Oct. 2 storms.

Bill Brunner, plant engineer at Lansing’s waste water treatment facility, said during heavy rainfall, the combined water and sewer pipes cannot carry any more water and excess is channeled into the rivers. Until the rain stops and the flow recedes, water and sewage continue being diverted into the rivers, he said.

Consistent rain during the last two weeks has led to more water going into the pipes because the ground cannot absorb more moisture.

“That really does have an effect,” Brunner said.

The most recent overflow began at 8 a.m. Oct. 11, and it stopped around 1 a.m. Oct. 12.

The bulk of the sewage and water went into the Grand River between the dam at Moore’s Park and St. Joseph Cemetery in the northwest section of Lansing, the city said.

Overflow into the Red Cedar River came from outfalls near the intersection of East South and South Cedar streets and from behind the Lansing Board of Water & Light facility on East Hazel Street.

Lansing’s sewer system has previously had issues with sewage dumping into the rivers.

The city continues work on separating the storm water systems to stop sewage from going into the rivers, but completing the project could take another 15 to 20 years.

“It’s something we’re trying to eliminate,” Brunner said.