ATTLEBORO - A County Street bridge project that neighbors complain is taking too long already got hit with a setback Wednesday when a fire destroyed a diesel engine being used to power a pump keeping the work area in the Seven Mile River dry.

Work had stopped for the day when fire broke out around 4 p.m. Firefighters knocked down the blaze quickly, but diesel fuel leaked onto the ground, and possibly into the river.

Booms were put in place to prevent the spread of fuel, but Deputy Chief Ed Greve said a small amount at most made it into the water.

"I'm relatively confident that very little got into the river," he said.

Greve said the engine was fed by a 50-gallon fuel tank that was just filled in the morning. Witnesses said the work area was dry when the fire started, but was filling with water shortly after the engine stopped. A cause for the fire wasn't immediately determined.

A spokesman for Aetna Bridge Co. from Pawtucket, which is building the bridge, declined to comment other than to say the fire is "still under investigation."

It was not immediately known if the project would suffer a long delay, but the state's Department of Environmental Protection was called to the scene to assess damage to the soil and water.

Assistant City Health Agent Chuck Flanagan said it's likely the DEP would require removal and replacement of soil where the fuel spilled.

A couple of weeks ago, a temporary dam used to keep the work area dry was breached, which delayed the pouring of concrete for the new span.

Last summer, nearby residents who must take long detours because of the project complained the work seemed to be taking a long time, but officials said it was on time and could even be finished before winter.

The official completion date is not until April.

GEORGE W. RHODES can be reached at 508-236-0432 or at grhodes@thesunchronicle.com.