Hanover — Neighbors opposed to a large athletic facility planned near their homes have opened up a new line of attack against Dartmouth College: sound.

In reviewing the sound studies that Dartmouth commissioned for a proposed 70,000-square-foot indoor practice facility off South Park Street, the neighbors contend they have discovered that the college’s Alexis Boss Tennis Center, built in 1999, is violating its permitted noise levels.

On Friday, the residents submitted a formal request to the Hanover Planning Board to revoke the Boss Center’s permit, looking perhaps to trip up the college in an ongoing battle over a large facility that Dartmouth hopes to build next to the tennis center and near their homes.

A letter to the board from seven neighbors cites what it calls Dartmouth’s “failure to conform to the statements, plans and specifications … upon which the Planning Board’s site plan approval was based” in 1999.

The neighbors said that a college contractor at the time predicted that sound from the tennis facility would not exceed “ambient” levels. But now, they say, they can hear mechanical noise from Boss at their homes — seemingly breaking a promise upon which the town gave site plan approval.

The main issue for this group of residents around Tyler Road, to the east of campus, is a roughly $17.5 million athletic facility that Dartmouth now proposes to build next to the Boss Center, a short distance from their neighborhood. The project’s site plan review has moved slowly in Planning Board meetings, with residents filing objections and requests for clarification to Dartmouth’s design.

One opposing abutter, Kelly Dent, is the board’s vice chairwoman. She has recused herself as a board member from discussions, but has participated as a resident and engaged a Concord-based lawyer, Philip Hastings, to lobby the board.

After months of discussion over lighting, shadows, sound, size, screening, and many other concerns, board members still have not found the application complete, which they must do before considering whether to approve or deny it.

On Tuesday afternoon, college spokeswoman Diana Lawrence said Dartmouth had asked for a continuance of that evening’s hearing — which, later that day, the board granted — in order to prepare responses to board members’ questions and “more fully explain the data.”

“Our sound studies show that there is no violation of the Boss condition regarding sound, as approved in 1999,” Lawrence said in an email. “That information has been provided to the Planning Board as part of the practice facility site plan hearings and will be expanded upon at the next hearing on that project.

“If the board finds that there is a violation based upon additional investigation, we will address it,” she added.

At Tuesday night’s meeting, the board briefly addressed the neighbors’ request, deciding to gather more information about the residents’ claim of a sound violation and consult attorneys as to how the process to revoke approval would work.

Hanover Senior Planner Vicki Smith told board members that they needed to review the facts and decide whether to pursue a revocation, at which point they would have to hold public hearings before taking the action.

Smith suggested that, if there were a violation, the Planning Board could work with Dartmouth to mitigate the sound, rather than withdraw its approval.

“If you don’t have a valid approval, it seems to me like you need to vacate the building,” she said.

Board members also postponed the practice facility discussion, which they are treating as a separate matter, to the end of the month.

The neighbors, for their part, anticipated Dartmouth’s response to their letter. The Aug. 12 missive says that, this year, college contractors measured noise levels in the neighborhood — including noise from Boss — and twice found them to be higher than what Dartmouth predicted in 1999.

The contractors submitted those reports in June and July of this year. In August, after attorney Hastings expressed concern to the Planning Board about the noise levels, the college’s sound experts said they had “overestimated” the sound from existing mechanical equipment, the letter said.

The Hanover Planning Board’s next regularly scheduled meeting is Sept. 6; the next practice facility discussion will take place Aug. 30.

Rob Wolfe can be reached at rwolfe@vnews.com or 603-727-3242.