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GRAND POINTE PARK — A year-long inspection of the plumbing is as complete as can be at this time.
Although the system was cleaned beyond the original contract terms, the company tasked with inspecting it was unable to access the full network of remote cameras due to restrictions from tree roots and debris.
Many limitations stem from the age of the century-old plumbing system and reduced natural flushing of the network as stormwater runoff is diverted into a separate system installed in the 1990s to reduce pollutants entering the state’s lakes and streams .
A color-coded map of the park’s 41-mile plumbing network highlights numerous sewers south of Jefferson and in the central portion of the northern half of the city that cannot be surveyed with video equipment.
“Evaluations indicate the need for ongoing system maintenance that includes spraying, root canal treatment and lining,” said Patrick Droze, a project manager at OHM Advisors, the park’s consulting engineers, in last month’s report. “A full asset management plan will be established over the coming years to prioritize the segments for this work. The projects are also based on rainy weather analyzes that have been carried out since 2018.”
One bugaboo in the city’s plan to increase the sewage system’s water-holding capacity to match the levels of the downpours that returned to thousands of basements in the summer of 2021 is the lack of subsequent rains, forcing engineers to test theoretical ways to expand the network’s efficiency.
In the absence of up-to-date real-world data, hydrological flow models are based on historical precipitation from 2019 to 2021.
“Once the flow measurement is complete, models for the flow meter locations are developed,” said Droze. “OHM used this to create four separate models for the 10-year, 25-year, 50-year, and 100-year repeat intervals.”
The worst storm was 2.34 inches last June, contributing to the highest monthly total of 3.61 inches.
“So far, most rain events have been relatively light,” Droze reported.
“We met with the (Michigan Department of) Environment, Great Lakes and Energy in late September to establish a working relationship (regarding) Grosse Pointe Park’s existing sanitation model,” said Nancy Russell, an OHM engineer.
After inspecting most of the pipelines and manholes, Droze recommended that the city proceed with an assessment of the entire system.
He said specific duties consist of:
* Identification of defects in construction, operation and maintenance of channels and shafts,
* Recommendation of various repair methods, such as B. Replacement of pipe segments, casings, sealing of joints and similar relining options for manholes;
* Prioritization and allocation of repairs and improvements,
* Determination of costs and
* Determination of the work to be done in 2023.
– Brad Lindberg