I'm trying to understand how they could be within 60 miles of DC in any direction and not have water. This region is full of creeks, rivers, streams, swamps, etc. Hell, Fredericksburg, VA is just under 60 miles to the south and you have the Rappahannock River cutting through the area. It would take a hell of a drought, over years, to dry that river up. A bit further to the west has you crossing both the Rapidan and Rappahannock rivers. They're much smaller at this point, but still a decent amount of surface water.
Oh, and the piney woods (and did I spy sandy soil?) they showed in this episode peter out much further south than 60 miles away. That was more NC (if near I95) terrain, putting them over 100 miles away.
They're coming from Atlanta, so they're traveling Northeast. Even if they came through the Shenandoah Valley, they would be in hill country by the time they hit within 60 miles of DC (that would be close to Linden, VA I believe). Again, no sandy soil and no piney woods as shown in this episode.
Chris