BANGOR, Maine — City officials are grappling with how to pay for a major infrastructure project at the wastewater treatment plant, which could run about $3 million higher than they first expected.
For more than five years, the city has set aside $1.8 million in its budget as a placeholder, knowing it eventually would have to replace the plant’s biofiltration system, according to City Manager Cathy Conlow.
In December, the city received a report from AECOM, the engineering firm it hired to provide cost estimates for the project. That report put the total cost at nearly $4.8 million.
“We just didn’t have a good initial estimate,” Conlow said. She informed the city’s infrastructure committee of the cost projection during a meeting Monday night.
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 microorganisms 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 microorganisms 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 Andrew Rudzinski, superintendent of the Bangor Wastewater Treatment Plant. 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.
Even that newer top layer is showing signs of wear and cracking, and the 23-year-old layers below are in far worse shape, Rudzinski said.
“We can point out sections of it now that are collapsing,” he said Tuesday. If the biofilter were to fail, the plant, which treats 8 million to 9 million gallons of wastewater per day from residents in Bangor and several surrounding communities, could face much more substantial problems.
Rudzinski said the original $1.8 million “placeholder” estimate likely fell significantly short because it didn’t take into account ancillary costs, such as removal and disposal of the old biofilters, the weeks-long rental of a crane to do the work and the repair of any structural or equipment problems found in the 23-year-old concrete tower. More modern biofilter media also could be more costly than it did in 1992, he added.
Now, Rudzinski and Conlow are grappling with how to keep the project’s costs down for the city and its wastewater ratepayers.
Conlow said the project wouldn’t affect property taxes, as it’s being handled within the wastewater budget. But residents could see changes in their sewer bills. It’s early to say what the impact could be, as Bangor is still a few weeks away from diving into its budget process.
“They’ll probably see some impact, but we’re going to spread it out over some years to keep any increase down,” Rudzinski said.
The city is working with AECOM to find ways to reduce costs associated with the replacement. Rudzinski is working to shift priorities, potentially delaying other projects to focus funding on the biofilter replacement, Conlow said.
The wastewater plant also could take out a loan from the State Revolving Loan Fund, which currently offers long-term financing for clean water infrastructure projects at 1 percent.
“We want to do it this year because the interest rates are so low,” Conlow said. “We’re worried that the environment might change. We knew this would be expensive.”
Rudzinski said he hopes to start the replacement in late spring or early summer 2016.
Follow Nick McCrea on Twitter at @nmccrea213.