A BOSTON ENGINEERING FIRM on Tuesday agreed to pay $5.5 million to settle allegations that it failed to make sure contractors complied with the company’s own design specifications in building a water and sewer system on Plum Island.

In 2000 and 2002, CDM Smith Inc. of Boston won contracts to design and oversee construction of a nearly $23 million water and sewer system on Plum Island that was completed in 2006. The system was financed with loans from state agencies and mandated by the state Department of Environmental Protection.

Problems first surfaced with the system in 2011, when a water main break revealed badly corroded iron pipes that had not been wrapped in polyethylene, as the CDM Smith design required. After an initial investigation by the Inspector General’s office, the state attorney general entered into negotiation with CDM, alleging the company failed to fulfill its oversight obligations under the contract. Under the negotiated settlement, CDM agreed to pay $5.5 million without admitting any wrongdoing.

Newburyport Mayor Donna Holaday
Newburyport Mayor Donna Holaday

The water and sewer system encountered more problems during the winter of 2015, when part of the system froze, leaving many homes without running water and the ability to flush toilets.

Newburyport’s problems with the water and sewer system figured prominently in an article in CommonWealth on how Plum Island was at risk from storms and sea water rise due to climate change.

Newburyport Mayor Donna Holaday declined to say on Tuesday whether the frozen pipes of 2015 were all part of the same problem.  “It’s open for debate,” she said, quickly adding that the municipality has taken a number of steps since then to prevent pipes from freezing in the future.

Newburyport will receive $5.3 million of the CDM settlement payment for repairs and any modifications needed for the water and sewer system. With fires a concern, Holaday said a top priority is to inspect all 160 hydrants on Plum Island, replacing any corroded bolts or pipe and wrapping existing pipe in protective polyethylene.

“The system is functioning fine right now, but we know there are areas on the island of concern,” Holaday said.

A correction clarifying the nature of the settlement was added to this story.