Work continues to repair manholes around city
<p>A crew from SuperTec Infrastructure Technologies works on a manhole last week on Creekview Drive. The manholes are being sealed so that groundwater can't leak into them and pass into the city's sewer system. Heidi Desch / Whitefish Pilot</p>
For another approximately two weeks crews will continue to repair manholes around town as part of a project aimed at minimizing the amount of groundwater that is entering the city’s sewer system.
The manholes are part of a project designed to minimize the infiltration and inflow that is getting into the city’s wastewater system. A second part of the project will take place in the fall with pipeline rehabilitation.
The manholes are rehabilitated, according to Jim Swain, owner of SuperTec Infrastructure Technologies, based upon what the problem is causing groundwater to enter them. About half of the manholes will receive a lining to stop water from entering them and the other half will have the area around the manhole cover cut out and replaced.
“The biggest problem is groundwater,” he said. “We make sure it’s completely sealed so that it stops water from pouring into the sewer.”
The liner is saturated at the job site with an epoxy, lowered into place in the structure, and a removable inflation bladder is put in place. The epoxy is then steam cured. When the job is completed the liner is bonded to the outside structure of the manhole.
“It builds a new manhole inside the existing one,” Swain said. “It seals out any infiltration.”
Whitefish has a wastewater collection system with over 58 miles of sewer main and portions of the system are more than 100 years old. Those sections experience a large volume of clear water flow — primarily due to the abundance of surface and groundwater sources, according to Public Works Director Craig Workman.
Workman has said the extraneous flow, known as infiltration and inflow, can exceed the capacity of the collector pipes and reduces the performance of the city’s wastewater treatment facility.
The current project includes about 35 manholes and rehabilitation of about 5,000 linear feet of sewer main set to take place this fall.
An infiltration and inflow mitigation study in 2006 in the city identified over 18,500 lineal feet of sewer main that was in need of repair. A project in 2011 to rehabilitate several thousands lineal feet of main was effective at reducing inflow and infiltration, but analysis performed in 2013 indicated that additional work was needed.
The results of the analysis yielded three specific drainage basins as the priority — Birch Point, City Beach and River Lakes.
Birch Point and City Beach are some of the oldest sections of the collection system and clear water has been found to be entering the system through old pipes. River Lakes is a new system, however, infiltration and inflow has been discovered in the area through poorly installed manholes.
Grants from the state Department of Natural Resources and Conservation and the Montana Treasure State Endowment Program will provide $625,000 in funding for the project. The manhole work is expected to cost about $316,000, while the pipeline rehabilitation is about $497,000.