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 

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.

Source: City of Pasco