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Wastewater treatment plant completion soiled by problems

 

Posted 8/02/16 (Tue)

Wastewater treatment plant completion soiled by problems

Tioga’s wastewater treatment plant project is experiencing delays, which are expected to last well past the original estimated completion date, which was July 1.
“The plant itself is online,” said Larry Anderson, engineer with AE2S, the firm heading up the project. 
Anderson said the quality of the treated water has  met the project design requirements and the Department of Health’s requirements since June 30.
However, a number of issues remain. The main problems began when an electrical building on the site tilted seven inches, breaking conduit and leaving the plant without any power. 
Further investigation revealed improper compaction of the soil around the north side of clarifiers that are used to separate solids from wastewater. 
Tests have not determined the extent of the unstable soils, but there is a concern further settlement of the soils will impact systems that support the plant operations. 
With the electrical building not functioning, the plant is currently being operated manually. Substantial completion of the project is expected this fall, at which time the plant will be fully automated and require little time from city employees. 
Until then, city employees are spending some extra hours operating the plant. 
“Do I have heartburn over this? Yes I do,” said Mayor Drake McClelland. 
Costs
The project cost the city $5.15 million for construction, engineering, and testing. 
The problems with soil compaction are not adding additional costs to the city for the project itself, for either construction or engineering.
McClelland said the city has incurred some extra expense from overtime costs, though.
“The city can’t afford all this flipping overtime,” McClelland said.
McClelland said, besides the wages the city must pay, the project is taking time that could be going to other city services that need attention in preparation for winter. 
AE2S met with subcontractors and city representatives last Wednesday to discuss the problems and identify a course of action to find solutions. 
Charles Vein, president of AE2S, said it’s normal to have some problems on a project of this size. 
“I don’t want people to be alarmed,” he said.
And with the exception of the compaction issues, the project has gone very smoothly without any meaningful change orders. He said the impacts of the compaction issues can be resolved. 
 “I have every reason to believe the contractor will correct the problems and do it right,” Vein said.
Solutions
Since the electrical building tipped, the soil under it was replaced with compacted soil. Vein said the building will not have any more problems. 
However, settlement of the soils will impact a number of supporting plant systems around the clarifiers without further action. 
Wes Dickhut, a geotechnical engineer with Braun Intertec, performed a number of analyses on the soil around the area to determine its level of compaction and potentially the cause of the soil settlement. 
Dickhut said a simple test of one specific area of the soil allowed him to push a probe four feet down, indicating at least some soil had almost no compaction. 
“I’m not that strong,” Dickhut said.
Braun Intertec, working under AE2S, is performing the technical analysis of the soils to determine how much settlement can be expected and what steps should be taken to prevent impacts to the plant systems.
These impacted systems include conduit on the east and west side of the electrical building, which have already settled and could be damaged as supporting soil settled further over time.
For the east side of the building, the team of engineers at the meeting discussed using a grade beam to connect to solid structures. 
For the west side of the building, the engineers discussed using flexible connectors to allow for settlement, but City Water Superintendent Jeff Moberg questioned this approach as movement would create more wear and tear, resulting in the need for repairs long after the contractor is gone.
The engineers decided a grade beam on both sides of the building will be needed to support the conduit.
Moberg also pointed out the area could see quite a bit of movement of heavy equipment in the area, including dump trucks for removing treatment byproducts. This would increase settlement, he said. 
A waste-activated sludge building is also possibly sitting on unstable soil, and Rice Lake proposed putting supports under the building that would hold it up. 
Moberg said this would leave space under the building when the soil settled, which is a prime breeding ground for snakes, as often happens under the floor of basements with such gaps between concrete and soil. 
Speaking after the meeting, Anderson said the supports were one of a few options they’re looking at, and they could leave a void under the building. 
No decision has been made for that building, but if these supports are utilized, the area under the building could be filled with grout to seal up the void, Anderson explained. 
Drastic measures
At a meeting Wednesday, the group floated the idea of just excavating all the bad soil and replacing it with solid material. 
“Let’s just fix it,” Commissioner John Grubb suggested. 
Such an approach would be time-consuming and costly, and it may prevent the plant from being complete by winter. 
City Auditor Abby Salinas asked how long such a solution would take. 
“I’d rather have the perfect solution for the taxpayers’ money,” she said. 
Speaking after the meeting, Anderson said a full excavation wouldn’t be necessary and dealing individually with the critical components will fully address the issues. 
Causes
Currently, tests have not indicated any leaks come from the plant, and as far as anyone can tell, the problem was caused when construction was conducted through the winter. 
Representatives of the contractor were not present at the meeting, and it’s unclear why they were unable to join the discussion. Multiple messages left for Rice Lake at its corporate offices in Deerwood, Minn., and the project manager were not returned as of press time.
Vein said AE2S has worked on a number of projects with Rice Lake, projects much larger than the Tioga wastewater treatment plant, and they’ve always displayed a high degree of quality in their work. 
“They are one of the best contractors we’ve dealt with,” Vein said. 
Speaking after the meeting, Salinas said the contractor was rushed to complete the project to meet deadlines set by the Department of Health, which forced them to do dirt work during the winter.
This results in a lot of frost in the soil and is considered a generally bad practice in construction. 
Vein said on a project this size, doing the work through winter is largely “unheard of” and were it not for the state mandates, they would have waited for the spring thaw.  
Salinas explained the DOH was pressuring the city to meet the service needs of a much larger population at the time. 
Since the expected growth did not occur and the population has actually decreased, the project will satisfy the city’s growth for years to come.
The DOH has since extended the deadline to complete the plant, and Salinas said the city should have done more last winter to request an extension to avoid these problems, especially as the city began to see the decline in population. 
Moberg asked Vein and Anderson why the soil problems weren’t detected before the construction of all the impacted systems, since a subcontractor performed tests on the soil.
Speaking after the meeting, Anderson said the soil tests were done by a contractor the city hired, and the company was not working under the project contractor or AE2S. 
Withholding pay
At Wednesday’s meeting, AE2S presented a pay request from Rice Lake, and Anderson agreed he’d relay the request to commissioners.
Salinas said it would need to come before the regular commission meeting on Monday, but McClelland and Grubb said they would refuse to consider it.
“We won’t entertain it at all,” said Grubb. 
Vein agreed that the project has not reached substantial completion at this time.