Wastewater Treatment Plant

The City of Monroe constructed its first wastewater treatment plant in the 1950’s to meet the increasingly stringent water quality standards of that era.  Since that time, the facility has undergone several improvements to keep up with increased regulations and to become more energy efficient.  The plant is primarily designed to protect public health, and the health of lower Skykomish River where it discharges 1.7 million gallons of effluent per day. 

Currently, the National Pollutant Discharge Elimination System permit provides the regulatory framework that drives the treatment processes.  Compliance with the permit ensures the quality of the water discharged from the plant is consistent with locally enforced standards. 

Operationally, the treatment process includes accepting inflow from the sanitary sewer and processing through mechanical screening, aeration, aerobic digestion, ultra-violet disinfection, composting, and odor control.  All of these processes are critical to protecting public health and our local riparian environment.        


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