Combined Sewer Overflows

The Everett wastewater collection system is divided into 2 areas: the north end combined sewer system and the south end separated sewer system.

What are combined sewer systems?
Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, the combined sewer system conveys all of the wastewater to Everett's wastewater treatment plant, called the Everett Water Pollution Control Facility (EWPCF), where it is treated and then discharged to either the Snohomish River or Port Gardner Bay. However, during periods of heavy rainfall or snowmelt, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system. This is why the combined sewer system is designed to occasionally overflow and discharge directly to the Snohomish River or Port Gardner Bay. These overflows are called combined sewer overflows (CSOs).
  1. Causes of overflows
  2. FAQs
  3. Reduction program

View or download information about Causes of Combined Sewer Overflows (PDF).