Nevada Drive Sewer Replacement
Client—Beacon Hill Water & Sewer District, Cowlitz County, Washington
The District hired Gibbs & Olson to evaluate the best methods for replacing 11,000 feet of existing aging corrugated metal and asbestos cement sanitary sewer conveyance piping. The original pipeline was constructed in the 1960’s within the ravines south of Nevada Drive. There is limited access to this piping with steep slopes and streams located near or adjacent to much of the pipeline route.
After evaluating construction methods, recommendations included replacing the piping in phases utilizing four different construction methods (open trench, cured-in-place pipe liner, pipe bursting, and horizontal directional drilling). The District hired Gibbs & Olson as the prime consultant to provide the surveying, environmental permitting, geotechnical investigation, cultural resource studies, design and construction phase services to replace the existing pipeline.
Gibbs & Olson collected survey field data for the existing sanitary sewer system which also included manhole locations, identifying parcels requiring easements, and stream bed locations. Working with an environmental subconsultant, additional information was collected to better determine the environmental permitting and mitigation required to construct the pipeline. An investigation including field reconnaissance by a cultural resources subconsultant was also performed to determine the likelihood of cultural resources being present within the project area. A geotechnical subconsultant performed a subsurface exploration and provide recommendations for the installation of retaining walls to construct a gravel access road.
The first phase of construction included installing 3,000 feet of 8-inch High Density Polyethylene (HDPE) gravity sewer piping using an open trench method, 5 manholes, 2,400 feet of a gravel access road and 400 feet of gabion walls. The access road was left in place after the phase one improvements were completed. This access road will be used for the next construction phases and will also provide long term access for maintenance of the sanitary sewer facilities. This first phase also included acquiring 23 easements across private properties.
The second construction phase is currently being designed and includes 8,000 feet of 6 to 8-inch HDPE piping and associated sewer manholes. The piping will be installed utilizing the four different construction methods previously mentioned. The second phase will include acquiring up to 40 easements across private properties. Additional geotechnical borings will be completed to provide the necessary geotechnical information for completing horizontal directional drilling and pipe bursting construction. A spider excavator will be used to excavate test pits in the steep areas with difficult access. Construction on the second phase is expected to begin in 2023.