I can't speak for Prince William County...however, here are the exemptions for disclosure under Virginia's FOIA:
http://law.justia.com/virginia/codes/toc0202000/2.2-3705.2.html
If your looking for radio communication structure information there might be a problem under the terrorism exemption.
"Plans and information to prevent or respond to terrorist activity, the disclosure of which would jeopardize the safety of any person, including (i) critical infrastructure sector or structural components; (ii) vulnerability assessments, operational, procedural, transportation, and tactical planning or training manuals, and staff meeting minutes or other records; and (iii) engineering or architectural records, or records containing information derived from such records, to the extent such records reveal the location or operation of security equipment and systems, elevators, ventilation, fire protection, emergency, electrical, telecommunications or utility equipment and systems of any public building, structure or information storage facility, or telecommunications or utility equipment or systems. The same categories of records of any governmental or nongovernmental person or entity submitted to a public body for the purpose of antiterrorism response planning may be withheld from disclosure if such person or entity in writing (a) invokes the protections of this subdivision, (b) identifies with specificity the records or portions thereof for which protection is sought, and (c) states with reasonable particularity why the protection of such records from public disclosure is necessary to meet the objective of antiterrorism planning or protection. Such statement shall be a public record and shall be disclosed upon request. Nothing in this subdivision shall be construed to prohibit the disclosure of records relating to the structural or environmental soundness of any building, nor shall it prevent the disclosure of information relating to any building in connection with an inquiry into the performance of that building after it has been subjected to fire, explosion, natural disaster or other catastrophic event."
Hope that helps....