Is this illegal?

[bobobb.livejournal.com]

I was walking in the Davis Square area and saw a man from a industrial cleaning company dumping his cleaning waste down the street sewer from his van -- it was pretty stinky.  I'm assuming this is illegal because when he saw me he packed up his truck and took off in a hurry.   When I looked on the city's web page I couldn't find anything about illegal dumping, so maybe I'm wrong.  I assumed that the street sewers go into the mystic river -- is this true?  Please fill me in.  I have his licence plate number so I'll report it if in fact it is illegal dumping -- but again who do you report this to?