Where Does the Black Stuff on the Snow Go?

Well it's finally warmed up enough to melt off most of the snow, but what happens to the layer of black crud on top of the snow? The snow turns to water and goes down the sewer and flows into the ocean killing off marine life with it's layer of sewage, chicken bones, and oil but where does the black stuff go? Does it just pile up in place until it rains? Does it flow to the ocean? These are the probing questions we need to asking in this time of warming because Barbara "soft focus" Walters sure as hell ain't asking them.