As much as a quarter of the water treated at the Manchester sewage treatment plant may be leaking into the system from ground water and runoff, causing the facility to treat thousands of gallons of water a day unnecessarily.
The problem, called inflow and infiltration, or I & I, is expensive because the town must pay for chemicals and electricity used to treat that extra water.
"We're treating water that we shouldn't be treating," said Steven Miller, Manchester's water and waste water superintendent.
"It's something that we're going to need to address," said Mayor Earl A.J. "Tim" Warehime Jr. But a solution is "something that takes money," he said.
I & I is common in older sewer systems, where deteriorating underground pipes and leaky manholes let in ground water and runoff.
"There's always some infiltration in systems," said Manchester Councilman John A. Riley, who oversees public utilities for the Town Council. "We have quite a bit of infiltration, by the way it looks."
From January through June, the Manchester sewage plant treated 52,756,000 gallons of water. The town pumped 39,242,700 gallons of water, which means that more than a quarter of the water treated leaked into the system. The problem worsens when it rains or snows, and rising water tables inundate cracked sewer pipes, enabling water to leak in.
The actual amount of water leaking into the system may be even greater, because many homes that are connected to the town water system have their own septic systems and do not discharge water into the town sewage system. Their water is included in the total amount pumped, but not the amount processed at the sewage plant.
In April 1993, when runoff from March storms seeped into the area's ground water, the Manchester water system pumped 6,166,400 gallons of water. The town's sewage plant treated 12,027,000 gallons of water that month, meaning about half the treated water had leaked into the system.
"That runs into money," Mr. Miller said. "It's basically double the chemical cost and double the electrical cost."
Mr. Warehime said the town's first step toward fixing the problem would be to examine the sewer pipes. That is done by sending a remote-controlled video camera through the pipes to find leaks.
When cracks are located, there are several ways to treat the problem. Sewer pipes can be fitted with a plastic liner that is inflated inside the lines.
"It may be cheaper to dig it up and fix it," Mr. Riley said. "There's a lot of factors you have to look at before you decide which way to go."
Improved manhole lids that keep water out are available at reasonable cost, Mr. Miller said.
"You get a lot of flow going into those manholes," he said.
Town Manager Terry L. Short said it is difficult to estimate how much the leakage has cost the town. He said he has not calculated any increased costs for electricity and chemicals.
If Manchester's infiltration problem were fixed, Mr. Short said, the town could wait until its population triples before expanding the sewage plant.
He estimated that the plant expansion would cost $12 million to $15 million.
By comparison, fixing the infiltration problem "starts to look cheap," he said.