Work on the CSO control program began in 1993 with a set of cornerstone projects designed to remove millions of gallons of stormwater from the combined sewer system before construction started on large tunnel and other control facilitilies.

Stream Diversion
Environmental Services constructed a pipeline that diverts Tanner Creek and smaller west hills streams from the combined sewer system to remove about 165-million gallons of stormwater annually from combined sewers.

Stormwater Sumps
About 3,000 stormwater sumps and sedimentation manholes in combined sewer areas throughout north, east and southeast Portland collect residential street runoff, trap sediment and pollutants, and allow water to soak into the ground.

Downspout Disconnection
Residents in combined sewer areas disconnected roof drains from combined sewers removing more than 1.2-billion gallons of stormwater per year from the combined sewer system.

Sewer Separation
Environmental Services eliminated combined sewers in key neighborhoods by installing new pipes to separate stormwater from sewage.