A sewer-like odor from an unidentified source is forcing the evacuation of several classrooms in the lower level of Major Edwards Elementary School.

Principal Thomas M. Caruso said the odor has been intermittent, but is occurring with greater frequency.

"We began noticing it in the late fall - it was faint, and would come and go. Last year, we never noticed it," he said.

Even more troubling than the odor is the difficulty the school is having in identifying the source of the odor.

Mr. Caruso said he has called upon several town departments, the town's sewer contractor and a plumbing contractor to help determine where the odor is coming from, but they have been unsuccessful.

"We have also worked with the Mass. Department of Public Health - Indoor Air Quality Division, and a private company, Diversified Environmental Corp.," Mr. Caruso said. "We have been assured by both that there is no health risk to students or staff, although the odor is unpleasant and unacceptable."

Attempts to eliminate the odor by cleaning plumbing traps, installing charcoal filters on vent pipes and checking for plumbing leaks have all failed.

"We've torn the place apart," Mr. Caruso said. "We've brought in the experts and they can't figure it out."

Until the problem is rectified, the Lifeskills classroom has been relocated to a different room, the stage is being used for occupational and physical therapy and the art and music teachers are conducting their classes in the students' regular classroom, rather than their own dedicated classrooms.

Superintendent Thomas Kane called the relocations "a precautionary step." "We've been told that there's nothing unhealthy. But that being said, we don't know what the problem is."

"It's a lot of disruption," Mr. Caruso said. "But we have to make the best out of a not good situation."

"It's been frustrating," Mr. Kane said. "We've had people in who should have the expertise, and they haven't been able to tell what the problem is. We're hoping to identify the problem (soon) and do whatever it takes to remedy the situation."