Grosse Pointe City exploring options to improve sewer system

By: K. Michelle Moran | Grosse Pointe Times | Published October 8, 2021

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GROSSE POINTE CITY — Following catastrophic flooding and basement backups this summer, Grosse Pointe City’s engineers were charged with looking at the City’s sewer system to see what, if anything, could be done to prevent this from happening again.

What they determined is that, while there are some ways to reduce or slow the amount of rain that gets into the sanitary sewer system, the price tag for some of those options is staggering, especially for a small community, and a real fix likely isn’t possible without a regional approach.

City Engineer Steve Pangori presented the Grosse Pointe City Council with an overview of their sewer system during a Sept. 20 council meeting. Pangori said there are four ways to improve the system: make sure it’s properly maintained and in working order, which appears to have been the case in the City; slow or reduce the influx of water into the system; increase capacity; and/or make modifications to homes and businesses.

The City has already televised storm sewers on slow-draining streets, resulting in the discovery of areas with tree roots, deposits and cracks, Pangori said. Making those repairs earlier wouldn’t have prevented basement backups and flooding, however, as Pangori said these intrusions actually slowed the influx of water into the system.

Disconnecting downspouts and roof drains that are still connected to the sewer system would slow the flow of water into the system, Pangori said. Downspouts should ideally go out at least 5 feet, if possible, to keep stormwater from getting into the home’s foundation, he said.

Green infrastructure is another tool the City can use to slow or reduce the influx of stormwater into the sewer system. Pangori said bioswales may be incorporated as part of a joint streetscape project with Detroit along Mack Avenue. City Manager Pete Dame said the City is also planning to incorporate green infrastructure in Parking Lot 4 in the Village.

Options for businesses and homes range from installing backflow preventers and sump pumps — which, when combined, would cost roughly $2,500 to $6,000 per home — to elevating plumbing combined with installing a sump pump, at about $7,000 to $10,000 per home.

For restaurants and other businesses that do food preparation, installing or maintaining a grease trap can help. This would eliminate grease, fats and oils from the sanitary sewer system, which can clog pipes. Dame said they’re looking at modifying the City’s ordinance on grease traps.

Almost every home in the City has separated storm and sanitary sewer lines, but the Village currently has a hybrid storm sewer system, with some lines draining rainwater into the lake while others are combined storm and sanitary lines that lead to the Neff Road pump station. Dame said they’re proposing complete sewer separation in the Village, which would increase capacity.

“There is stormwater capacity throughout the whole system,” Dame said.

Also to increase system capacity, Pangori said the City could redirect storm sewers north of Waterloo Avenue from the pump station to Lake St. Clair, but that would come with a price tag estimated at $15 million to $20 million.

One of the most expensive options would be to build an underground stormwater detention system at Elworthy Field. For a system that could hold water from a 10-year storm event — 3.29 inches of rain — the estimated cost would be $40 million to $55 million. For a 50-year storm event — 4.52 inches of rain — the cost would be about $52 million to $73 million. For 6.7 inches of rain, which is the rough amount that fell between June 25 and 26 — it has been said to have been a 1,000-year storm — the cost would be approximately $78 million to $110 million. Then, there’s the fact that the Grosse Pointe Public School System leases Elworthy Field from the City, meaning that any project there would need to pass muster not only with City officials, but also with school district officials.

It’s no wonder, then, that some of these options will likely never be undertaken.

“This does not seem very feasible,” Mayor Sheila Tomkowiak said, referring to the underground detention system.

Cost, and the fact that multiple communities send their sewage to Great Lakes Water Authority facilities for treatment, mean that this is something no single municipality can tackle on its own.

“It will take a comprehensive approach to really improve the City’s (ability to prevent) flooding … and we can’t do it ourselves,” Dame said.

Even before the June storm, GLWA was already planning to replace its aging Conner Creek Pump Station, which is where the City and multiple other communities direct their sewage.

Several east side communities — including the City — recently began meeting to discuss a possible regional project to prevent future basement backups.

City officials plan to continue looking for viable ways to address increasingly powerful storms, and Dame said there will be a further engineering review of the storm sewer system.

“We’re all hoping to have a good solution to these problems,” City Councilman Daniel Williams said.