Water Treatment Process

Forest Grove Water Resource Recovery Facility

The Forest Grove Water Resource Recovery Facility, located on Fern Hill Road in Forest Grove, is a nationally acclaimed, state-of-the-art facility serving Washington County residents in the cities of Forest Grove, Cornelius, and Gaston. Despite being one of Clean Water Services’ smaller facilities, Forest Grove is one of the most complex treatment facilities in the Pacific Northwest.

The Forest Grove facility treats an annual average of 7 million gallons of used water each day to among the highest safety and quality standards in the nation. In addition to advanced biologic processes, the facility welcomed the planting of over a million native plants, which transformed the former effluent lagoon ponds into the 92-acre Fernhill Natural Treatment System that harnessed the capabilities of natural systems to improve the quality of water before its discharge to the Tualatin River. 

This facility is connected to two of our other facilities, which aids in mitigating peak flows and helps treat the water and remove valuable resources. During wetter months, the system conveys excess flows through preliminary processes before sending the water to the Rock Creek facility. Staff also dynamically alter the flow path of the facility to react to flood conditions. During dryer months, flows from the Hillsboro facility to Forest Grove for additional treatment. 

Forest Grove was originally constructed in 1951 and has seen numerous transformations to its treatment process over the years. This facility centralized a scattered system of inefficient wastewater treatment plants, creating one of the most efficient and advanced facilities in the world.

Forest Grove water resource recovery facility aerial View

Forest Grove Water Resource Recovery Facility Process

Used water flows through a series of processes (PDF): preliminary, secondary, disinfection, and the Fernhill Natural Treatment System — before the cleaned water is discharged to the Tualatin River.


Fernhill is part of more than 700 acres in Forest Grove owned by Clean Water Services for water resources management. Fernhill utilizes natural treatment systems, or wetlands, to improve water quality by removing nutrients and cooling and naturalizing the water after initial treatment at the Forest Grove facility. In the summer, 5 million gallons of water are cleaned each day at Forest Grove and then Fernhill before flowing to the Tualatin River. 

CWS acquired Fernhill in 2006 and in 2014 90 acres of old sewage lagoons were transformed into treatment wetlands by draining the ponds, then drying and excavating more than 200,000 cubic yards of soil into precise contours and depths. Using 15 control structures and 2,400 feet of piping, the water was managed to encourage the growth and establishment of over a million native wetland plants and four billion seeds, planted both for water quality and for habitat. 

Explore Fernhill’s innovative design. Fernhill is a place to explore trails, observe wildlife, learn about water, and enjoy nature. Learn more at fernhillnts.org.

Forest Grove Facility Facts

  • Provides a higher level of treatment over many activated sludge systems, as it utilizes biological phosphorus removal in the facility and nitrogen removal in the Natural Treatment System
  • Operates 24-hours a day, 365 days a year
  • Serves a growing population of over 20,000 people
  • Meets over 1,500 permit conditions, including monthly, weekly and daily limits established to protect the Tualatin River
  • Cleans an average of 7 million gallons of wastewater per day
  • Takes advantage of resource sharing by utilizing the Rock Creek facility for solids treatment
  • Supplies flow to the Fernhill Natural Treatment System which improves the quality of water before its discharge to the Tualatin River
  • National Association of Clean Water Agencies (NACWA) Gold Award for 100% permit compliance achieved over multiple years