By SUE SUCHYTA
Sunday Times Newspapers
RIVERVIEW – City officials hope the Downriver Utility Wastewater Authority will authorize the connection of a new relief sewer to the Downriver Regional Storage and Transport System, to alleviate the Huntington subdivision basement backups.
The city used a 2017 Stormwater, Asset Management and Wastewater program grant to determine how best to alleviate the subdivision’s ongoing flooding.
Maria Sedki, vice president and senior civil engineer at Fishbeck, Thompson, Carr and Huber, said the construction of a relief sewer at Stratford and Huntington roads, to the existing DRSTS tunnel, would help eliminate the problem through the construction of a 50-foot deep manhole, with a 30-foot drop to the DRSTS.
She said the passive system would have a low operating and maintenance cost, with the potential to convey excess flow from storms larger than a recent 25-year, 24-hour rain event which swamped the subdivision four years ago.
On Aug. 15, 2016, 3.1 inches of rain fell in seven hours, with 0.9 inches of rain falling in 15 minutes during the storm’s peak. Two days earlier, 1.3 inches of rain had fallen, leaving the area ground already saturated.
Connecting to the DUWA line would be able to convey more flow than a storage basin, and the connection would be less expensive to construct than other engineering options, Sedki said.
Should DUWA deny the city’s request to connect to the DRSTS, the city could pursue a more expensive alternative, the construction of an equalizing basin, which could retain high flow during periods of fluctuation, such as rain events.
The SAW grant study estimated, in 2017, that the cost to construct an EQ basin would run $4.84 million, while a relief sewer to the DRSTS would cost $3.21 million. In the three years since the study, project prices have increased in response to inflation.
To accommodate a catch basin, Sedki said a relief sewer would be constructed at Stratford and Huntington roads, with an 18-inch relief sewer to a proposed pump station, leading to a 215,000-gallon EQ basin, which would discharge wastewater back into the system gradually after a rain event.
Sedki said enlarging the sewer line to its existing connection point to the interceptor line is not a practical option.
Drysdale said a bond would likely be needed to finance the infrastructure investment.
He said the annual bond payment per year, for a $5 million bond, over 20 years, would be $300,000 to $350,000 annually, which would add about 1 mill onto the city’s taxes, or it could be added to the city’s water debt rates.
“This is one of those projects that I don’t think you can ever set enough cash aside to do, but it is something that is very needed,” Drysdale said. “That is the area that, whenever we have rain, that we have a lot of issues.”
City Councilman James Trombley said the Huntington subdivision has been flooded multiple times.
“If there is something possible that we could do, to make this happen, I’m all in,” he said. “I feel for those residents over there every time we get a big rain. They need help.”