There are several food trucks parked at this location. For one of them, it was obvious that food oil had been dumped, flowed down the driveway and into the street, which would then be washed into Sligo Creek. It looked like this had been happening for a while. Melanie Isis, Executive Director of the Takoma Langley Crossroads Development Authority, was the first to notice this and point it out.
Google street view shot from July 2015, so this has been
happening for more than a year. The stains are much worse now.