In older neighborhoods in Seattle we have what are called
Combined Sewers. Combined Sewers are used for both waste water
(sewage from inside the house) and storm water (all the water
flowing off the roof, driveway, sidewalk, road, etc). Combined
Sewers cannot handle the entire amount of water during heavy
rain events and are designed to overflow so that raw sewage
doesn’t back up into your home. When they overflow a combination
of raw sewage and storm water is discharged into nearby bodies
of water like Lake Washington, Lake Union, Elliot Bay, the
Duwamish River, and Puget Sound. Besides the raw sewage, oil
from the road, pesticides and fertilizer from your garden and
other toxins are sent untreated into our environment. The
Federal and State government have legislated that only one CSO
(combined sewer overflow) shall occur each year. According to
Seattle Public Utilities: • We average 318 Overflows per year
during the wet season, October through May. • In Ballard alone
on average 43 million gallons overflow