Leschi Sewer Improvement

What & Why

The Leschi Sewer Improvement project is part of Seattle Public Utilities’ effort to address a city‐wide challenge of Combined Sewer Overflows (CSOs) into our waterways.

The project was issued physical completion in October 2016. This project replaced and repaired sewer pipes along Lake Washington. SPU is currently installing monitoring equipment along the updated sewer line to start one-year post construction performance monitoring.

Project goals and benefits

Many Seattle neighborhoods have a sewer system that mixes raw sewage from our homes and businesses with polluted runoff from our roofs and streets in a single pipe – a “combined sewer.” During dry weather, sewage flows to the wastewater treatment plant. When it rains, polluted runoff overwhelms the pipe that carries raw sewage. The raw sewage and polluted runoff overflow into the nearest waterway. SPU must reduce the number of times this happens by improving the sewer system in parts of Seattle. We are required to limit each outfall to one overflow per year to meet state and federal requirements. It’s also the right thing to do to protect our waterways and sustain our quality of life.