VASSALBORO — Until it built the current system of treatment plants in the early 1980s, the town’s raw sewage was pumped directly into Outlet Stream, running through the middle of the town.

Now the aging system is beginning to show cracks, and officials are looking at options to upgrade or replace it entirely.

Rather than invest in a new treatment facility or upgrade its current system, Sanitary District board members are leaning toward linking up with Winslow’s sewer system and pumping waste to the Kennebec Sanitary Treatment District in Waterville.

Experts warn that given its age and condition, the town’s system of three sand filter treatment facilities is beyond the end of its useful life and may even be at risk of collapse.

But even though the system is in critical need of replacement, the projected $5 million price tag to connect to Winslow is a huge outlay for the town’s tiny user base to sustain.

“It’s a sad situation, but it has to be done,” said Sanitary District Board Member Alfred Roy in a interview Tuesday. “We have no alternative.”

The current system was built in 1982 and hasn’t been upgraded since the early 1990s. The expected life cycle of the facilities is 20 years, according to Richard Green, an engineer with Hoyle, Tanner and Associates, which studied and evaluated the Vassalboro system.

Sanitary District trustees began considering a new system more than a year ago, and the firm submitted its report to the board in December.

The town has three treatment sites, two in North Vassalboro and one in East Vassalboro that collect wastewater for treatment in large septic tanks. Partially treated effluent is pumped into open sand beds and drains into an underground system before it is disinfected with chlorine and discharged into Outlet Stream.

Even though the system is still effective, it is far beyond its useful life, according to Green.

“It’s living on borrowed time,” he said Tuesday.

In his report, Green noted that many of the mechanical components in the facility are worn out and pumps and controls have been replaced, sometimes on an emergency basis. Possible sudden equipment failure “creates a health risk due to the danger of possible overflows or backups,” Green stated in the report.

Further, because of the age and “steady deterioration” of the system, the sand filters are no longer operating as designed. Although the amount of useful life left in the filters is impossible to predict, when they start to fail the entire system could fall apart rapidly.

The report also notes that Vassalboro’s discharges contribute to the high concentrations of phosphorus in Outlet Stream and could hinder an effort to restore alewife population from Sabasticook River to China Lake.

Even with all its problems, Vassalboro does not regularly exceed its permitted discharge levels, although outflow can spike during heavy rain and spring melt, said Chuck Applebee, a contractor from Winthrop-based Water Quality and Compliance Services that operates the system.

“You shouldn’t go away with the impression that there is a problem there all the time, because there is not,” Applebee said.

But he agrees that the system is on its last legs.

“They haven’t had a catastrophic problem there yet, but it’s probably not too far away,” he said

In his report, Green outlined six options including constructing new treatment plants in North and East Vassalboro, combining the flow to a new North Vassalboro plant, pumping to a new land treatment system, and connecting to the Kennebec Sanitation Treatment District.

But while the upfront cost of connecting to KSTD is the same or less than building new treatment plants, lower annual operation and maintenance costs make it a preferable option over the long term, Green said. With a drawdown in industrial clients, the Waterville plant easily can accommodate the 77,000 gallons that Vassalboro produces daily, he estimated.

However, the $5.19 million cost of constructing the system and the $171,000 needed annually to run it is expected to send user rates soaring.

Even if the Sanitation District is looking for grants and other sources of funding to help pay for the work, ratepayers should brace for step hikes in their bills. In his report, Green suggested that the system’s cost could add more than $1,000 to the annual bills.

Applebee said the cost would unlikely to be that high, but could add up to $600 for an average user.

Until a financial package is put together, the effect on rates is impossible to calculate, he added. A household income survey showed the average customer had earnings of $30,000 per year, which could put the district in a good position for getting grants, Applebee said.

While upfront costs might be high, future rates might be lower if Vassalboro connects to the Waterville plant, said Sanitary District Chairman Ray Breton.

The district’s 191 users currently pay double the rate of surrounding towns for sewage treatment, he noted. Connecting to a bigger system could help decrease those rates on par with other towns.

Roy, the other board member, estimated that he and his wife alone pay $140 every three months for sewer service. The base rate for a home that isn’t even treating water is $72 a quarter.

The district board will hold a public hearing on the proposal at 6 p.m. March 23 at the Vassalboro Town Office.

Peter McGuire — 861-9239

pmcguire@centralmaine.com

Twitter: @PeteL_McGuire