Snohomish Sewage Lagoon Reservoir Report

Last Updated: December 15, 2025

Located in Everett, Washington, the Snohomish Sewage Lagoon serves as an essential water resource infrastructure managed by the local government.


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Summary

This lagoon, constructed in 1958, plays a critical role in treating sewage and maintaining water quality in the Snohomish River-Offstream. With a storage capacity of 400 acre-feet and a surface area of 120 acres, the lagoon is designed as an earth dam with a hydraulic height of 11 feet.

The Snohomish Sewage Lagoon is regulated by the Washington Department of Ecology, ensuring compliance with state permitting, inspection, and enforcement requirements. Despite its low hazard potential, the lagoon has not been rated for its overall condition. The facility's emergency action plan status, risk assessment, and risk management measures are currently undocumented, highlighting potential areas for improvement in emergency preparedness and response. As a vital component of the local water infrastructure, ongoing monitoring and maintenance of the Snohomish Sewage Lagoon are essential to safeguarding water resources and mitigating environmental risks in the region.

Year Completed

1958

Dam Length

5000

River Or Stream

Snohomish River-Offstream

Primary Dam Type

Earth

Surface Area

120

Hydraulic Height

11

Drainage Area

0.14

Nid Storage

400

Structural Height

11

Hazard Potential

Low

Foundations

Soil

Nid Height

11
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.