The stormwater system collects rain that falls on impermeable surfaces—that is, buildings, roads and parking lots that prevent water from being absorbed directly into the ground—in storm drains and catch basins on roadways and parking lots. While this water is not as dirty as wastewater, it can contain significant pollutants such as motor oil, road salt, pet wastes, winter sand and other chemicals.

Many of the pipes in Augusta carry both wastewater and stormwater, whih are commonly known as "combined sewers".

Heavy rains can cause combined sewers to overflow into the environment. These events are called Combined Sewer Overflows (CSO) by the Environmental Protection Agency. In response to this issue, and concerns raised by customers over the years, GAUD convened a Stormwater Work Group to review our stormwater system management, and the rate structure for catch basins and ERUs. Learn more about the history of combined sewer overflows in Maine.

Our long-term goal is to reduce the frequency of combined sewer overflows—and we have already cut CSO volume by 90%! One method to further reduce overflows includes storing large amounts of combined sewer during wet weather events. To this end, we recently completed a one million gallon storage tank under Mill Park to capture CSO during storm events. Combining this storage facility with new pipes and pumps has eliminated CSO into Bond Brook.

We are also gradually separating combined sewers into both sewer and stormwater pipes to reduce the amount of runoff water going into the combined sewer.