Strava map of where runners run shows that the McMillan reservoir and sand filtration site are popular routes for runners (who use the Strava app, that is)

See this post from Washington City Paper Housing Complex reporter Aaron Wiener:

This Is Where Washingtonians Bike and Run

Posted by Aaron Wiener on Apr. 29, 2014 at 2:18 pm

His post includes two maps from Strava, an app to log runner's routes (among other features). 

Here is the second of the two supplied maps, which shows the routes that runners using Strava like to take.

Note that heavy red borders around the McMillan Sand Filtration site and the McMillan Reservoir site.

No surprise!