Flooding at Union and Mill streets during Tropical Storm Lee in September 2011. Occoquan leaders and residents fear an approved development near the town will make flooding worse. (Town of Occoquan)

The development isn’t a big one — Oaks III is a 32,500-square-foot office building and one home at the corner of Tanyard Hill and Old Bridge roads. And while flooding in the town has been an issue for years, dozens of residents who packed the McCoart building’s board chambers — and many who sat on folding chairs and watched on video screens outside — said the town simply could not handle the storm water that they fear will roll down the steep terrain from the office building toward the town’s center.

Many also described the endless line of cars that creep down Tanyard Hill Road every rush hour, and the potential dangers of office workers turning onto the two-lane thoroughfare, described as a paved “cow path.”

But in the end, on a 5-3 vote just after 11 p.m., the majority of county supervisors said residents would benefit from increased office space and a plan that called for preserving land with a permanent conservation easement — with development rights handed over to the Northern Virginia Conservation Trust — on 75 percent of the property.

Board Chairman Corey A. Stewart (R-At Large) along with Supervisors Maureen S. Caddigan, John D. Jenkins (D-Neabsco), Peter K. Candland (R-Gainesville) and W.S. “Wally” Covington III (R-Brentsville) voted for the project.

Supervisors Michael C. May (R-Occoquan), Martin E. “Marty” Nohe (R-Coles) and Frank J. Principi (D-Woodbridge) voted against the rezoning proposal.

Flooding is fresh in many residents’ minds, as the town center was inundated when Tropical Storm Lee brought storms in September.

But Stewart said rejecting the rezoning proposal would not help fix the town’s stormwater problems, which have been exacerbated by uphill development over the years.

“The real problem is that two-thirds of the county’s workforce commute outside the county every single day,” he said. “The only way in the long term is to have more employment in Prince William County.”

Some residents — wearing stickers saying I “heart” Occoquan and “Oaks III” crossed out — said that if the developer Ken Thompson had been willing to work with the town to address concerns, many might have supported the project.

The town’s opposition, “could have been avoided by spending some time with the town of Occoquan,” said town Mayor Earnie Porta. “But he refused to do so.”

Thompson held one meeting in June with town officials and residents, which came after the county Planning Commission had recommended the project for approval. County staff also recommended the project’s approval, and said that the project’s stormwater management system on the site would adequately capture water.

Several residents also spoke in support of the project. Many of them lived in the Lake Ridge and surrounding communities, and said Thompson, who has developed in Prince William for decades, has a good reputation and should be granted the right to bring more commercial space to the county.

May questioned county staff about the project’s traffic assumptions, which he and others said would create a dangerous situation as Tanyard Hill, the slim, two-lane road that goes through the town and serves as a cut-through for hundreds wanting to head to Route 123, meets Old Bridge Road, a main thoroughfare in the area. There is no traffic light planned.

“It usually involves someone dying to get a light,” said Chris Blouin, who lives in the area. “I see real problems with this.”

Developers made one change to the project to address concerns about increased traffic from the site going through the town, just before the public hearing Tuesday. Vehicles won’t be able to turn left out of the office complex onto Tanyard Hill Road toward the town, said Pete Dolan, Thompson’s attorney.

Coincidentally, just before taking up the Oaks III issue, supervisors approved a project called The Haven at Fortuna Village, described as an upscale apartment complex that would sit just east of Fortuna Center Plaza and Dumfries Road in Potomac. The project was approved unanimously, and a representative for the nearby residences said that the developer had worked carefully with neighbors and addressed all their concerns.

“Ultimately, you got to a point where the neighboring community could support the project,” May said of the contrast. Principi suggested supervisors delay the vote so the town and developer could meet further. But Stewart said that the disagreements were fundamental and wouldn’t solve any problems, and the motion was defeated 5-3.

“Consistently through this process, we’ve been ignored,” said James Phelps, who helped organize opposition to the project.

Porta said after the vote that he would consider the town’s limited options with the rest of the Town Council. He was proud that so many residents showed up to voice opposition, despite the result.

Several said they were surprised at Stewart’s support — he is the district’s former supervisor. “Corey Stewart was re-elected multiple times saying that he was going to protect towns like Occoquan from developers like this,” said Porta, who thought supervisors had put developers’ future campaign checks ahead of the town’s concerns.

Stewart had fought much larger proposals at the site, and he told residents that Oaks III was a good option, especially because the majority of the land on the site would stay preserved.

But those arguments didn’t sway residents, who said after the vote they were surprised supervisors were unconcerned about the way the developer handled the project. “We didn’t say ‘no’ to the building, we said ‘compromise on it,’” said Denise White, an Occoquan resident, after the vote. “I’m totally shocked. I can’t believe they would not make them go back to the table.”