11th Street Combined Sewer Overflow Separation Project

Client—City of Astoria, Oregon

Gibbs & Olson provided surveying, design, and construction phase services for the City’s combined sewer overflow (CSO) separation project. This $6 million project physically separated the stormwater from the sanitary sewer system and included over 18,000 feet of new storm, sanitary sewer, and water piping. Located within an urban residential area, the project site posed unique challenges including routing buried pipelines through two large, active landslides; and addressing shallow groundwater and groundwater springs surfacing through pavement cracks. The project also presented an opportunity for the City to address other issues including poor roadway and sidewalk conditions on extreme slopes of up to 28 percent. In addition to the storm, sewer and water system improvements, there was 3,000 feet of roadway constructed with associated curb, gutter and sidewalk and new pedestrian ramps.

The 11th Street project received an Engineering Excellence Honor Award from ACEC Oregon in January 2015.

A paper presenting the technical challenges of designing pipelines through active landslides was selected by ASCE and presented by Gibbs & Olson and Shannon & Wilson at the ASCE National Pipeline Conference in September 2014 in Portland, Oregon.