In 1969, Oregon's Department of Environmental Quality placed a temporary halt to new construction in Washington County. On February 3, 1970, ten cities and sixteen sanitary districts combined to form the Unified Sewerage Agency (USA). Later that year, voters in the new district approved a $36 million bond measure to consolidate, construct and upgrade USA's regional public wastewater treatment facilities. The Durham Wastewater Treatment Facility opened in 1976, which replaced 14 smaller treatment plants. Two years later six more treatment plants were replaced with the opening of the Rock Creek Wastewater Treatment Facility.