540 signatures are needed. Virginia does not allow straight recalls -- instead, if enough signatures are gathered, a judge is empowered to decide whether to kick the official out.
Good history here:
In 1997, a similar recall petition drive was launched against then-Sugarland Run District Supervisor Steven D. Whitener (R), who was accused of bullying two female supervisors. Whitener faced board sanctions, including being stripped of his committee assignments, and a recall petition signed by 283 voters in his district. In court, the judge threw out the petition and chastised board members for bickering. The board’s authority to sanction board members for their conduct was upheld in a federal lawsuit filed by Whitener.