Wastewater Treatment


The Wastewater Division operates within the Public Works Department and is responsible for managing all facets of wastewater treatment for the City of Pasco to meet and exceed state and federal requirements for the safe return of water to the Columbia River. The division consists of 10 staff members.

The Treatment Process

  1. Remove foreign materials in the wastewater.
  2. Primary treatment-settable solids are removed from the wastewater at the primary clarifiers.
  3. Secondary treatment includes biologically converting ammonia contained in the plant influent to nitrate.
  4. After secondary treatment the wastewater is disinfected with ultraviolet light prior to returning to the Columbia River.
  5. Solids are thickened in the primary clarifiers, transferred to the two primary and two secondary digesters.
  6. Digested biosolids are dewatered on drying beds and applied to agricultural land as a soil amendment.

Wastewater Treatment Plant Facility Plan

The City has developed a Wastewater Treatment Plant Facility Plan in conformance with current legislation and Washington Department of Ecology guidelines.  This Plan assesses the City's current and future needs for wastewater treatment and disposal to ensure compliance with effluent quality requirements.  A series of projects have been identified to address those near and long-term needs. Department of Ecology approval for this Plan was issued on August 26, 2019.

WWTP Improvements - Phase 1

The Wastewater Treatment Plant (WWTP) Phase I project consists of improvements and modifications to the City's existing municipal WWTP which includes; furnishing all labor, materials and equipment necessary for the construction of new primary effluent structures and piping, two new aeration basins, alterations to two existing aeration basins, a blower building expansion, addition of two new blowers, modifications to two existing blowers, RAS pump system distribution improvements, a new effluent flowmeter facility, approximately 1,150 feet of new 42-inch diameter outfall piping, new primary power switchgear, associated electrical and control systems, associated site work and yard piping, and other appurtenances as necessary to complete the project. The WWTP improvements also include the demolition of the existing trickling filter and select items.

This project is being funded through low-interest loans from the Washington State Department of Ecology. Total estimated project cost: $27M

  • Design Engineer: Murraysmith, Inc. 
  • Contractor: Clearwater Construction & Management, LLC. 
  • Construction: HDR Engineering, Inc.

Time-lapse and live camera of the construction site HERE

WWTP Improvements Phase 2 

This project improves water quality in the Columbia River through the construction of the City of Pasco's municipal Wastewater Treatment Facility by replacing components of the plant that have exceeded their useful life and expanding the plant to meet the projected demand of the forecasted population growth for the City. This project will refurbish existing infrastructure and enhance the treatment capabilities of the City of Pasco's WWTP. 

This Project is Phase 2 of improvements and completes the expansion and replacement of aging infrastructure for the municipal facility. 

This project has been divided into two separate bid packages to reduce overall cost, as the uplands and inwater work will be performed by two different specialty contractors. Phase 2A is the outfall replacement, and Phase 2B is the plant work. Phase 2 improvements will address several of the plant deficiencies noted in the facility plan for the solids handling and disinfection systems. Additionally, the water-based outfall replacement work included in the Phase 2 Improvement project is critical in addressing the outfall hydraulics. Replacing the undersized outfall piping and multiport diffuser is necessary for the City of Pasco to accommodate the expected increase in flows based on the rate of growth of the sewer system. 

This project is being funded through low-interest loans from the Washington State Department of Ecology. Total estimated project cost: $35M

  • Design Engineer: Murraysmith, Inc. 
  • Contractor: TBD
  • Construction: TBD

Tour the Wastewater Treatment Plant

Free tours are available of the city's Wastewater Treatment Plant. The tour is approximately two hours in length and includes a walk-through of the plant and a more detailed explanation of the plant's processes.

Advance reservations are required. Call (509) 545-3468 for more information.