http://www.fairfaxcounty.gov/dpwes/stormwaterordinance/chapter_104.pdf
See page 7 item (m)(5) refers you to Code of Virginia Title 45.1
Best to ask the Fairfax County Department of Public Works and Environmental Services
http://www.fairfaxcounty.gov/dpwes/
Primary Phone #: 703-324-5033
Address: 12055 Government Center Parkway Suite 659, Fairfax, VA 22035-5502