One question I hear a lot is “doesn’t stormwater get treated centrally before it gets discharged anyway?” The short answer is ‘no.’ Although most stormwater systems used to go through through the same treatment as sanitary sewer, most urbanized areas have replaced the combined sewer system with two separate systems, one for stormwater and the other for sanitary sewer.
What this means is that there is no centralized treatment for stormwater. There are exceptions where a regional stormwater system has been constructed for the use of the few properties that are immediately adjacent. However, those cases are few in number and shrinking. Any treatment stormwater receives, then, is limited to whatever treatment systems there are on the individual site where it was generated. While there are very good treatment systems in use today, they all require diligent maintenance to function properly. If maintenance is inadequate, the runoff stormwater quality will also be inadequate.
We all need to do our part, then, to ensure that stormwater is kept clean and that pollutant loads discharged to downstream rivers, bays, and groundwater is kept to a minimum. The way to do this is to ensure that the stormwater features on site are kept functioning properly. Proper maintenance, including following manufacturer’s recommendations for cleaning cycles and calling a professional when you have a concern, are very important for ensuring water quality for everyone.
– See more at: http://www.catchallenvironmental.com/blog/centralized-stormwater-treatment-or-lack-thereof#sthash.Vvi4G8LW.dpuf