Big Gulch Sanitary Sewer Reconstruction Project
A Brief Historical Overview

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Looking Back

When we started action we were the Olympus Terrance Sewer District (OTSD). Then mid-way through the project we merged with the Mukilteo Water District and are now the Mukilteo Water and Wastewater District (MWWD). The original Board of Commissioners from OTSD remain involved in the project together with the new Commissioners from the Mukilteo Water District. We are now one Board overseeing the completion of this large and complex project.

Originally the sanitary sewer lines serving the City of Mukilteo (City) all drained to the north to the City’s Wastewater Treatment Plant near the ferry dock. In 1969, Olympus Terrace Sewer District built a Wastewater Treatment Plant to service areas outside of the City’s service areas. This plant and its sewer trunk lines were located in the Big Gulch Basin. The City increased in size and added sewer service to additional areas by way of Local Improvement Districts (LIDs) that increased flows to their treatment plant.

In the 1980’s, the City’s treatment plant was not able to meet Regulations for Discharge and unable to accept more flow. In 1981, a major LID was created by the City that included a Sewer Lift Station which sent a large portion of the City’s wastewater to the Olympus Terrace Treatment Plant down the Big Gulch Sewer line. In 1991, the City then built another lift station that totally replaced their failing treatment plant. The City has annexed additional areas so that all of the original Olympus Terrace Sewer District is in the City limits and OTSD has been treating a major portion of the City of Mukilteo’s wastewater since that time. The majority of these sewerage flows were directed to a connection point that flowed to the 52nd Street trunk line to Big Gulch. From here one main trunk line was constructed adjacent to Big Gulch Creek to the treatment plant at the bottom of the gulch. A second sewer trunk line was also constructed down into Big Gulch which joins into the Big Gulch trunk about half way down at the 52nd Street line.

At that time, the land through which these trunk lines were constructed was owned by the Standard Oil Company. An easement was conveyed to the District for the placement, construction, operation and maintenance of these trunk sewer lines. A few years later ownership of the land now called Big Gulch was conveyed to the County and again later to the City. Today the large undeveloped tract of land through which the districts trunk sewer lines cross remains owned by the City.

These sewer trunk lines were constructed by OTSD in 1969 – 1970. This occurred well before zoning and environmental laws existed. These pipelines were constructed using standard cut-and-cover methods, designed with an estimated life span of fifty years. A backhoe dug a trench adjacent to the Big Gulch Creek, the new sewer pipe was placed into the trench and then backfilled. The new pipe was buried an average of seven to ten feet deep.

When these trunk sewer lines were constructed, those areas surrounding the top of the gulch were undeveloped. After the new sewer system was built, development started to occur.

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