Stonington — Two years ago, the Water Pollution Control Authority decided to begin a project to divert 300,000 gallons of sewage a day from the Mystic treatment plant, which was reaching the limit on how much sewage it is permitted to treat, to the underused borough plant.

The diversion, which began to operate a few weeks ago, was aimed at ending the two-year-long moratorium on new sewer hookups in Mystic and making sure the Mystic plant operates within the limits of its permits. The end of the moratorium would allow for new homes and businesses, some of which have zoning approval and paid sewer connection fees, to be built and connect with the sewer system. 

But the WPCA recently learned that even with the diversion, the Mystic plant is still at times exceeding its permit limit of 800,000 gallons per day.

And the exact reason for the increased flow is not known. 

Among the possible sources of the additional flow into the plant are the increased number of people visiting Mystic this summer, homes that illegally use sump pumps to discharge flood water into the sewer system and infiltration of ground water into existing pipes that then has to be treated at the plant. The authority has completed the first of two phases of an infiltration and inflow, or I&I, study of the latter problem. Authority members have agreed to urge the consultant doing the study to accelerate the second phase to help determine exactly where water might be leaking into the system.

On Tuesday night, authority members met to discuss whether or not to lift the moratorium, which poses the risk that the plant would further surpass its treatment limits and expose it to enforcement action by state and federal officials.

WPCA Director Doug Nettleton has said that while some days the plant is treating as much as 900,000 gallons of sewage after the diversion, there are days where it falls below 800,000. He added that the plant is not consistently far enough below 800,000 to begin accepting large amounts of new sewage flow. 

Authority Chairman Rich Cody said Tuesday that the authority wants to give people relief from the moratorium but also has to watch its permit limits. 

"We're supposed to help economic development, ensure we have clean water and comply with DEEP (state Department of Energy and Environmental Protection) requirements," he said. "It's a real balancing act."

Alan Contillo, owner of Mystic Coastal Flooring, is one of those waiting to hook up to the system after building four condominiums above his Old Stonington Road store.

At Tuesday's meeting, he told the authority he had invested $1 million in the units but cannot sell them.

"I have no money coming in and a lot of debt," he said. "We're just little guys. We're trying to make a living."

There are housing and hotel projects, as well as individual homeowners who are waiting for the moratorium to be lifted or eased so they can proceed with their projects.

In addition to trying to accelerate the second phase of the I&I study, authority members agreed to take several other steps in advance of their September meeting. 

Nettleton will compile a list of properties waiting to connect, such as whose owners have paid sewer connection fees. The authority will collect data for August to see how often and by how much the plant exceeded its permits. It also will investigate the design capacity of the plant compared to the permit limits to see if it could get approval to treat more sewage as well as whether another 100,000 gallons of sewage could be diverted to the borough plant. Nettleton also will discuss these issues with DEEP.

Whatever the solution the authority comes up with to address the immediate issue with the Mystic plant, Nettleton said it will be a "short-term fix that won't last long." The authority had thought the diversion would have given it a five-year window to plan a long-term solution.

"At some point, the town will have to bite the bullet and say, 'What are we going do for the next 30-50 years?'" Nettleton said.  

That long-term fix could mean the construction of a single plant with adequate capacity to serve the entire town. The project has been discussed in the past but the town decided to continue to upgrade its three aging plants in Mystic, the borough and Pawcatuck.

Along with funding the cost of a new plant, which could hover around $75 million to $100 million, the town would have to find a location, determine a discharge point for the treated water and install piping to get the sewage there. It is estimated it would take at least five years to design and permit a new plant.

In 2010, town residents approved an $18.3 million plan to upgrade the three plants, and last year, the town approved another $10 million to make needed repairs to the town's three sewer plants and 17 pumping stations. In 2005, residents objected to the WPCA's $42.9 million plan to build a new plant behind the high school.

j.wojtas@theday.com