Storm water run off is generated when rain and snow melts and flows over land or
impervious surfaces (paved streets, parking lots, and building rooftops) and does
not soak into the ground. Storm water accumulates debris, chemicals, sediment, nutrients
and other pollutants that adversely affect water quality of nearby lakes, streams
Don’t Storm Sewers Treat Storm Water?
Yes and No. Storm sewers are typically separate from waste water or sanitary sewers.
In more developed areas, like cities and towns, residential and commercial waste
water is conveyed through sanitary sewers to waste water facilities where it is treated
to meet water quality standards before it is discharged. However, storm water is
usually conveyed through an underground system of pipes and then is discharged, without
treatment, to a nearby lake or stream. In some cases, storm drains and inlets have
integrated treatment devices such as sumps, which allow for some settling and collection
of sediments or oil/gas chambers, which separate out oils an gas from the rest of
the storm water. Most storm sewers, however, do not include these types of devices
due to expense, required maintenance and difficulty retrofitting existing structures.