FAIRFIELD — A big $64 million upgrade to the waste water treatment plant comes with an even bigger question: Who should chip in to pay the bill?

“I think that’s the elephant in the room,” Mark Elletson, chairman of the Water Pollution Control Authority, told the Board of Selectmen recently while updating the board on the status of the project.

First Selectman Mike Tetreau said the choice is to either have a general tax increase on all property owners, or an increase in fees paid by sewer users.

“One of the components and one of the things for me is service fees,” Tetreau said. “Our top users, some of them are not taxpayers. Our No. 1 user, Fairfield University, would not be paying if the funding is out of property taxes.”

While a decision didn’t need to be made right away, Tetreau said, it is time to begin the discussion.

Selectman Edward Bateson said the last time the town had this discussion, it was when the plant was upgraded to remove nitrogen that would go into Long Island Sound. At that time, the idea was to fund the project through general taxation with the “rationale that everyone benefits from clean water,” whether they were a sewer user or not.

“There’s not a right or wrong way,” Tetreau said, “just a different perspective.”

Tetreau said it doesn’t seem fair to all the taxpayers if the top users are paying toward the upgrades.

“We have Sacred Heart and Fairfield, both going gangbusters, and their share of the business will continue to increase,” he said, as the two colleges continue to add buildings. “We at least should look at that part of the formula.”

Fees are based on the user’s water consumption. There are about 17,200 households connected to the sewer system. According to the WPCA, a rough calculation shows a household using 100 cubic feet would pay an additional $217 a year, or $18 a month for 20 years.

The last major project cost $29.4 million and, like Bateson said, was paid through the town’s general fund. A $6.9 million principal balance remains from that project and will be paid off in July 2022.

Bateson also raised the issue of the plant’s capacity. Elletson said the project would not increase capacity, but would simply replace aging equipment.

“The issue is the age of the equipment,” Elletson said. “If you conceptualize 9 million gallons of waste water coming into the plant, and visually look at this equipment and know there’s no plan B for this equipment, if there’s a failure we’re all going to be saying, ‘How did we let this happen?’ ”

Elletson said by ferreting out and repairing “hot spots” where there is an infiltration by other water sources, they have been able to reduce the daily flow into the treatment plant. The average daily flow is around 7.5 million gallons, down from 9 million. He said new plumbing fixtures are also becoming more efficient as far as reducing water usage.

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