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Rainfall and Flow

Rainfall and flow

Seattle’s annual average 38 inches of rainfall significantly influences the volume flowing into West Point Treatment Plant’s combined wastewater and stormwater system. Treating this rainwater, in addition to wastewater, increases energy consumption. Across our collection system, the infiltration and inflow of stormwater and groundwater into sewer lines through cracks, holes, joint failures, and direct connections can also account for upwards to 60 to 70 percent of the flow.

Air Temperature

Outdoor air temp

Annual average outdoor temperature ranges between 40 and 66 degrees and even colder temperatures off Elliott Bay can impact our shoreline facilities considerably. Anaerobic digester feed systems need to maintain a temperature of about 98 degrees to sustain microbial metabolic functioning.


Fuel cost and population

As more people move to our region, WTD must add capacity to the system. With careful planning, treatment plants are able to treat increased volumes of wastewater from residential and business sources. Accommodating increased capacity also means accommodating community expectations that wastewater treatment services are safe, reliable, thorough, and do not negatively impact property values.

Odor Control

Control of odors has become a primary design consideration for most collection and treatment facilities. As development encroaches on WTD facilities and as new facilities are built, controlling nuisance odors is an important step toward mitigating WTD’s presence in a community. Odor reduction involves forcing large volumes of fouled air through scrubbers such as carbon filters – an energy-intensive process that contributes to energy consumption regardless of the quality or quantity of water treated.Odor control

Wastewater Treatment Technologies

WTD’s goal is to meet or exceed our permit standards in all facets of operation. While the  environmental benefit of treatment is undeniable, each level of treatment requires incrementally more  energy. Primary and secondary treatment technologies remove a majority of the suspended solids and  dissolved contaminants found in wastewater. Advanced treatment technologies further improve the  quality of effluent to meet regulatory limits for recycled water that can be used for non-drinking  purposes.

 Treatment technology and energy use

For more information about the Energy Program, please contact us at: