The City of Mill Creek is proposing to replace an existing damaged 36” CMP stormwater main that extends north-south under the Sweetwater Ranch neighborhood perpendicular to 144th Street SE. The original stormwater main was constructed prior to the development of the neighborhood and is located within an existing 30-foot utility easement that includes portions of four residential properties. In 2018, the stormwater main was found to be in an advanced degree of deterioration and emergency repairs were completed. Since the repairs, another sinkhole was found on private property near the previous repairs. Further inspections determined that the original pipes downstream of the repairs have significant damage.
The project will replace the existing stormwater main with new pipes while avoiding and minimizing impacts to two wetlands, steep slopes, adjacent neighboring properties, and utilities.
The project will specifically abandon the existing 36-inch CMP by filling it with flowable grout, shift the alignment slightly west, and install approximately 444 feet of 36-inch plastic storm sewer pipe with four concrete catch basins using conventional cut and cover trenching techniques.