Va. Code § 15.2-1728
In any case where exclusive jurisdiction over any property or territory has been granted by the Commonwealth to the United States government, or to a department or agency thereof, the governing body of any contiguous locality or the Division of Capitol Police may enter into a mutual aid agreement with the appropriate federal authorities to authorize police cooperation and assistance within such property or territory. Subject to the conditions of any such agreement, all police officers and agents of the contracting governing body or agency shall have the same powers, rights, benefits, privileges and immunities while acting in the performance of their duties on the property or territory under federal authority as are lawfully conferred upon them within their own jurisdictions.
Va. Code § 15.2-1728