UPDATE: As of 5:45 p.m., Belmont Ridge Road has reopened.
Loudoun County Fire and Rescue workers are on the scene along the 20500 block of Belmont Ridge Road "investigating an incident."
A fire-rescue representative would not not describe the situation other than to call it an incident.
"Fire-Rescue is working with staff of the facility to determine what course of action, if any is required," Loudoun Fire & Rescue spokeswoman Mary Maguire said. "Due to fire-rescue operations along Belmont Ridge Road, the road is closed as a precaution."
It's not yet clear to which "the facility" Maquire was referring. Fairfax City has a water plant in the area, which is also near the Luck Stone Quarry.
An alert from Loudoun County indicated the road would remain closed until 6 p.m.