South Central Force Main Replacements Preliminary Design – Kitsap County, WA

Project manager for the preparation of a preliminary design report that investigated and evaluated alternatives for replacing 3,300 feet of 12-inch AC sewer force main with 12 or 14-inch force main (Schedule 1) and 6,500 feet of 30-inch Techite sewer force main with 30-inch force main (Schedule 2). Transient analyses were conducted on both projects using MWH software. HDPE pipe was selected for both projects for its corrosion properties, reduction in transients, and reduced vulnerability to seismic events.

Schedule 1 was situated in County roads while Schedule 2 was situated in open pastures, woodlands and wetlands/streams and required acquisition of easements. Schedule 1 included investigation and evaluation of four alternatives/options: 1) parallel replacement with a 12 or 14-inch force main; 2) replacement with a 12 or 14-inch force main using pipe bursting; 3) abandonment of a lift station with installation of a 15-inch gravity sewer and; 4) extending the sewer force main to a lift station. Project costs for Schedule 1 were estimated at over $4 million.

In addition to different pipe materials and use of trenchless technologies, two different alignments were investigated for Schedule 2: 1) parallel replacement and; 2) alternative alignment for a portion. As the force main could not be shut down, hot tapping and line stopping were required at both ends of the project. Assisted the County with public involvement. Project costs were estimated at $12.9 million.