Sinkholes reach critical level
Sinkholes from last year’s flooding are reaching a critical point on both sides of the Muskingum River in Marietta.
Last Friday, one portion of sewer line collapsed on Post Street and now sewage is being transported above ground from one manhole to the next down the line via a loud, whirring pump and a rubber hose.
Meanwhile on the west side, the failures along Virginia Street, Gilman Avenue, Market Street and Fort Street have made sinkholes too deep for in-house repair, according to Wastewater Superintendent Steve Elliott.
“They’re all larger waste lines,” he explained Thursday. “Where the problems start is where the joints in those lines are.”
He said the Harmar lines are all clay tile pipes put in some time in the 1960s running 18 to 20 feet below the surface.
“So years of high waters and flooding, even river levels of 28 feet, put pressure on those lines and shifted the soil around them to allow the joints to open up,” explained Elliott.
Fourth Ward Councilman Geoff Schenkel said Friday he has heard concerns from Harmar residents about the sinkholes, wondering whether the 2016 sewer boring project between the Harmar Lift Station and the Lafayette Hotel parking lot resulted in the current collapses and blockages.
“People have asked if their foundations are in danger when looking at the sinkhole on Fort Street and as I drive the path from Virginia to Gilman to Fort and the pumphouse, it seems to follow that pathway under the river then,” he said.
For more than three months last year Virginia Street at Gilman Avenue was closed due to its sinkhole, and orange cones still offer motorists a visual cue to move cautiously around the other four sinkholes.
But the 2016 summer project is not believed to have been the catalyst for sinkholes from 2018, said Elliott.
“This is a longer-term wear and tear issue, and we’ve looked at a lot of different ways to tackle the problem,” he explained. “We looked at replacing with entirely new pipes, even installing another pump station, but the experts we’ve consulted believe that boring wouldn’t have done this.”
He said camera evidence from within the lines that can be accessed point to a degradation of the joints in the lines over the last half-century, rather than a single event.
While Elliott, the city engineer and consultants with Pickering and Associates are still “fine-tuning” the cost of repairs for both sides of the river, Elliott said estimates point at a minimum pf $464,000 but said costs could reach near or above $700,000.
“It’s a major project, and both what happens first and the cost may still change because Post Street is now an emergency,” he said.
But rather than just piecemeal repair for each failed point in the lines, he said the plan is to look more holistically at the sewer line system serving the west side and serving Front Street businesses between Butler Street and the Ohio River.
“We perceive that if we do not line these pipes entirely, we’ll just be chasing problems down to the next joints and the price will continue to grow exponentially,” he said.
At least at Market Street, Post Street and potentially Virginia Street, excavation will need to occur.
“In clay tile pipes, as those joints spread over time it creates voids in the surrounding soil,” Elliott explained. “At Market Street, the pipe is 18 feet deep so we’ll have to excavate and repair the bad section of the pipe that has sunken, but we don’t believe they have yet collapsed.”
Then to prevent further sinkholes and total collapse elsewhere along the system, a lining will be strung through the pipe structures.
“That will seal the spots where there are voids and should extend the life of the pipes another 50 years,” said Elliott.
Elliott said he anticipates a discussion with Marietta City Council’s Water and Sewer Committee to take place next week and to request authorization to pursue emergency funding.
At a glance:
• Five sinkholes have reached a critical level in Harmar and downtown Marietta this month.
• Post Street has a partially closed section where a sewer line has collapsed.
• Virginia Street, Gilman Avenue, Market Street, and Fort Street on the west side each have sinkholes indicating potential collapse.
• The failures first became apparent in the 2018 winter flooding.
• Emergency funding may soon be requested of Marietta City Council for the repairs.
Source: Marietta Wastewater Superintendent.