If you're in Alexandria proper, there is the Masters program at Chinquapin.
http://www.l4swimming.org/
Swims are Monday - Friday 6:00am - 7:30am; Tuesday, Thursday, and Friday 12:30pm - 1:30pm; Sunday 4:00pm - 5:45pm. In the summer, Monday, Wednesday, and Friday 1230-130pm workouts move to Cameron Street Pool in Old Town.
A quarterly pass is $210 and a 10 session punch pass is $90.