Wastewater Treatment

Sewers were first installed in 1892 throughout the developed areas of Bellingham. Consisting of heat-hardened clay pipe, the sewers collected both sewage and rainwater and discharged into Whatcom Creek and Bellingham Bay. Starting in 1908, probably because of sewer overloads, some storm sewers were installed in developed areas of the city.

Most of these early sewers are still in use. The ones carrying sewage have been intercepted ahead of their discharge points, and flows are now pumped to the wastewater treatment plant. Original storm water connections into sewers have since been disconnected.

The City first provided primary wastewater treatment in 1947, discharging effluent into a shallow part of Bellingham Bay, from a treatment plant located near the mouth of Whatcom Creek.

Post Point Resource Recovery Plant

In 1974, Bellingham replaced the Whatcom Creek treatment plant with the Post Point Resource Recovery Plant at 200 McKenzie Avenue. The Post Point Resource Recovery Plant began providing primary treatment for up to a peak flow of 55 million gallons per day (mgd) for the areas served by sewer. In addition, the City’s wastewater flows into the plant from over 250 miles of sewer collection mains located in Bellingham and the surrounding community. Septic tank waste is also collected from private homes throughout Whatcom County and brought to the plant for treatment.

In 1993, Post Point was upgraded to include secondary treatment at a cost of $55 million. This upgrade to secondary treatment increased contamination removal to 95% before releasing it into Bellingham Bay.

The City’s Comprehensive Sewer Plan identified the need for additional wastewater treatment capacity at the Post Point Plant. A Facilities Planning process began in late 2009, aiming to complete the plan in 2011. Construction was completed in 2014.

The video below provides an overview of how wastewater is cleaned and treated at the Post Point Resource Recovery Plant. ​

Preliminary Treatment

Preliminary treatment conditions the wastewater by removing materials which can harm or plug plant processes. It also contains a receiving station for residential septic tank sludge which is generated countywide.

The wastewater is pre-chlorinated and aerated to control bacteria and reduce odors. It then flows through coarse screening bars where rags and other large debris are removed. From there, the water enters the grit chamber where it slows down to allow sand and other heavy particles to settle out. This material is diverted to an incinerator and burned. The wastewater then goes to the primary treatment process.

Primary Treatment

In primary treatment, the wastewater flows into large basins called primary clarifiers.  The water remains in the primary clarifiers for approximately two hours.

While there, the suspended solids (primary sludge) settle to the bottom and oil and grease (scum) rise to the surface where they are skimmed off and sent to solids handling for disposal.

Secondary Treatment

Aeration Basin

Secondary treatment uses micro-organisms (activated sludge) to remove pollutants from the wastewater. The wastewater flows into large, enclosed aeration basins. Here, activated sludge is mixed with the wastewater and pure oxygen is added to create a perfect environment for the microorganisms to trap and remove contaminants.

Secondary Clarifiers

The water then flows into large clarifiers where the organisms can settle to the bottom. Some are removed and incinerated and other organisms are returned to the aeration basins to begin the process again. At this point, the water is nearly 95% pure. The treated wastewater then goes to the disinfection process.


Following secondary treatment, wastewater spends an hour in the chlorine contact chamber where chlorine is added to kill any remaining disease-causing organisms. Sodium bisulfite is added following the treatment to neutralize the chlorine to protect fish and sea life.

Microscopic protezoan help treat wastewater before it is discharged into Bellingham Bay

Microscopic protozoan help treat wastewater before it is discharged into Bellingham Bay. Laboratory personnel continually monitor the treatment process to ensure that the water released into the bay is safe for the environment. Samples are collected throughout the treatment process and tested to ensure the plant is functioning at optimum efficiency.

For more information about the Post Point Resource Recovery​ Plant please contact the Operations Supervisor in the Operations Division of the Public Works Department.

Plant Effluent

Following treatment, the water is discharged into Bellingham Bay from an outfall located a quarter mile offshore at a depth of 60 feet. The Post Point Wastewater Treatment Plant achieves 95% removal of organics and solids in the treated effluent.  Effluent discharged to Bellingham Bay has a biochemical oxygen demand (BOD) concentration of 9 parts per million (ppm) and a total suspended solids (TSS) concentration of seven ppm.

For more information about effluent quality please contact the Laboratory Supervisor in the Operations Division of the Public Works Department.

Solids Handling

Secondary solids are placed on a gravity belt, where polymer is added to thicken the sludge.  Excess water is then removed from the primary and secondary sludge by high-speed centrifuges. 

The sludge is incinerated in two multiple-hearth gas-fired ​incinerators at a temperature of 1500 degrees Fahrenheit, which reduces the volume by approximately 80% and destroys all pathogens.

Exhaust gases pass through two scrubbers and an electrostatic precipitator to protect air quality.


The City of Bellingham operates a state-certified laboratory. The laboratory performs compliance testing for the plant’s National Pollutant Discharge Elimination System (NPDES) permit and process control testing for each unit process. For treated effluent water quality information, please see the Effluent section.

For more information about the laboratory and monitoring programs please contact the Laboratory Supervisor at the Operations Division in the Public Works Department.


State-certified plant operators are on duty 24 hours a day to monitor and control the treatment process. The plant is fully automated and has a state-of-the-art computer system which provides operators with accurate and up-to-date information.

Educational Information

Visit the Environmental Education Site for Videos, Written Curriculum, and Tours.