Residents of the Knolls subdivision in northwest Columbus say they believe their neighborhood is under siege from the elements.

Already burdened by a storm and sanitary-sewer system that often can't handle current capacity and heavy rains, the community's residents said they are facing another threat from a proposed 402-unit apartment complex on the northwest corner of Olentangy River and Henderson roads.

On the service road that runs along the eastern edge of the subdivision and parallel with Olentangy River Road, traces of lye remain from a sanitary-sewer overflow nearly two months ago.

Storm water is somehow seeping into the sanitary sewers and the water pressure is blowing off manhole covers, causing sewage to spill over, resident Tom Swain said.

Columbus sent teams in hazmat suits to clean up the mess and put down lye to kill the remaining bacteria, Swain said.

Unfortunately, the sewage often comes dangerously close to storm-sewer intakes, which drain into the Olentangy River, he said.

In newer housing subdivisions, the storm and sanitary sewers are not connected.

Swain said it's unclear what is causing the backup, but it has become apparent storm water is breaching the sanitary system.

Just where isn't clear, he said.

"That's what I'd like to know," Swain said.

George Zonders, spokesman for the Columbus Department of Public Service, said the city is working to address the problem.

"Our department, and specifically the division of sewerage and drainage, has received quite a bit of feedback recently related to the sewer concerns in this area and we are aware of the challenges that these portions of our sewer system can pose during periods of wet weather," Zonders said.

A large capital-improvements project -- the Lower Olentangy Tunnel -- that is expected to begin construction in 2021 and be completed in 2025 should address the current issues, Zonders said.

In the meantime, the city is continuing to study the area to see if there might be an opportunity for some short-term improvements that can be implemented sooner than 2025, he said.

"All requests for connection to the sewer in this area will be fully analyzed by our office to ensure the health, safety and welfare of our residents is maintained and that conditions are not worsened by short-term development and growth," Zonders said.

Part of the problem, according to Swain, is 600 apartment units have been built in recent years in the area. Another 215 units are under construction at the site of a former strip club on Old West Henderson Road east of Henderson and Kenny roads.

All of that has contributed to the flooding, according to Swain, although Zonders said he could not verify the assertion.

NR Investments is the Florida-based developer that wants to build the 402 apartments in five buildings on what is known as the Zimmerman tract at 4497 Olentangy River Road.

During an Aug. 7 meeting with the Northwest Civic Association and residents, attorney Michael T. Shannon, who is representing the developer, said there is plenty of sewer capacity to accommodate the apartment complex, which wouldn't affect the Knolls.

However, the developer asked the project be tabled while research is completed on the sewer system.

On Aug. 8, the Columbus Development Commission also tabled the matter at the request of NR Investments officials.

Nick Cipiti, president of the Northwest Civic Association, said his "hope is to get all the facts on the table."

Cipiti said he is encouraged the developer asked the NWCA and the Columbus Development Commission to put the project on hold.

"It only makes sense to stop because we're getting conflicting reports from a number of different sources," he said.