North Stonington — About a month after it was declared complete in terms of its contract, the dam at Hewitt Farm — and the bridge that goes over it — has yet to opened to traffic.

The $455,000 dam project, First Selectman Nick Mullane said, still needs railings for safety and a wing wall to prevent future erosion — items that weren't included in the original contract with Mattern Construction Inc. Both were unforeseen results of the larger than originally planned 45-foot spillway that replaced two smaller ones, he said.

At an April 28 Board of Selectmen meeting, Mullane encouraged sticking with Mattern Construction to finish the wing wall, which the company said it could do for $11,300. At the time, Mullane said the project was under budget by about $50,000.

Just weeks later, Mullane changed his mind. The last couple of invoices the construction company sent to Town Hall, Mullane said Tuesday, were much higher than the town expected.

He said the wing wall likely could be completed at or under $5,000 using a combination of on-site stones and town employees with only a mason contracted out.

If given approval, Mullane said, he could have the wing wall and railings finished in two weeks. But Testa said the town might have no choice but to go out to bid for a project that may cost more than $5,000, and no action was taken Tuesday night.

George Mattern, owner of Mattern Construction, said Thursday that he believes there is only one item about which the town and his company disagree. That $100,000 item, which involved draining the waterway and building a cofferdam — a barrier installed to isolate the work area from the water — was a lump sum item, not to be paid per square foot or per any other measure.

Mattern said he received 50 percent of the payment upon dewatering and cofferdam installation, but then only 5 percent more at the end of the project.

"We have done quite a bit of this work," Mattern said. "We have never been not paid in full for a lump sum item."

Mattern said the town said they paid only 5 percent because the cofferdam wasn't installed to the size outlined in the plan and because the cofferdam flooded on a couple occasions. Mullane said Thursday he didn't want to get into the details of the dispute because it would be unprofessional and unproductive.

Mattern reiterated that the item wasn't to be based on square feet and said his company took the required steps to clean up the cofferdam when it flooded. If Mattern Construction doesn't receive the additional $45,000 from the town, he said, he sees no choice but to take legal action.

"I hate to do that," Mattern said, adding that his company completed the dam a day early. "We finished the job to the town's satisfaction. We would like to be paid in full and move on."

Parts of the conversation about the dam — first regarding questions about the oversight of work at the dam, then regarding invoice disagreements — have been in executive session every week since March 10. Mullane said Wednesday the intent all along has been to prepare for litigation Mattern might file.

The cost dispute comes as the town of North Stonington is waiting to find out whether it will be awarded funds from the state Department of Energy and Environmental Protection. The town has had its name in the pot for $450,000 toward the dam project for almost three years, Mullane said Tuesday.

Rep. Diana Urban, D-North Stonington, said Tuesday that the town was on a priority list for the funding last year, but that its paperwork was incomplete. She said she alerted the town to the issue a couple months ago.

Mullane said the town, once it received the mitigation grant request form, filled it out within 10 days and sent it off about three weeks ago.

The town remains on the priority list, Urban said.

l.boyle@theday.com

Twitter: @LindsayABoyle