BANGOR, Maine — Bangor’s expensive overhaul of a vital piece of its wastewater treatment system won’t be quite so costly after all.
Monday night, the city council approved a nearly $2.3 million construction bid by Auburn-based T Buck Construction to replace the biofiltration system at the city’s wastewater plant. It was the only bid the city received.
“We’re quite pleased with the bid,” said Andrew Rudzinski, superintendent of the Bangor Wastewater Treatment Plant. “It came in substantially lower than what was anticipated.”
In fact, it’s less than half the amount the city was warned it might have to pay.
Several years ago, city staff set aside $1.8 million in the budget as a placeholder for the project. But they were in for a surprise earlier this year when an engineering firm put the estimate closer to $4.8 million.
When the Bangor plant completed a major expansion in 1992, it added a concrete tower filled with eight layers of plastic biofilter media, made up of large blocks that resemble a honeycomb.
Stacked on top of one another, those eight layers are about 16 feet thick. If you were to stretch them out into one flat layer, the plastic would cover about 104 acres. All that surface area provides room for micro-organisms to grow and intermingle with wastewater. After flowing into the plant, the stormwater and sewage has solids, sand, oils and other materials removed before the liquid is sprayed onto the filters. The micro-organisms growing in the biofilters feed on the waste and continue the process of cleaning the wastewater until it’s clean enough to flow into the Penobscot River.
The projected lifespan of that biofilter is about 12 years. By now, most layers are into their 23rd year, according to Rudzinski. He said only the top layer has been replaced — twice in the past two decades. That top layer suffers the most wear and tear because it’s exposed to the sun and elements.
The setup is unusual among Maine wastewater facilities, so no one had a good idea of what it might cost to purchase and install the replacement biofilter, or what structural repairs would need to be done to the tower during construction, Rudzinski said.
“It’s not like bidding prices on asphalt or concrete,” he added.
Rudzinski said he hopes to start the work as soon as possible, but it may take some time to find the large quantities of biofilter media needed and have it delivered.
Crews should have the work completed by Oct. 1 at the latest, he said.
During construction, the tower will be shut down, so the wastewater will have to bypass it. Rudzinski said the plant will be able to keep up without the use of the biofilter system, and that the water the plant puts out should meet state and federal standards. He said water quality would be monitored throughout the construction process while the tower is out of operation.
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