48-Inch Plant Effluent Pipeline: Twelve Miles in Twenty-Six Days

The County Sanitation Districts of Los Angeles County (LACSD) operate the Palmdale Water Reclamation Plant, which is currently undergoing an expansion that will ultimately result in tertiary treatment for approximately 22 million gallons per day (mgd) of flow in the Antelope Valley. The plant effluent is utilized for agricultural irrigation, however during the winter months when plant flow exceeds the agronomic demand of the agricultural reuse sites, the effluent will be stored in lined reservoirs located 12 miles from the plant. A 12-mile long plant effluent force main was constructed to convey plant effluent to the reservoirs during the winter. The 48-inch high-density polyethylene (HDPE) pipeline also serves to return the effluent to agricultural sites adjacent to the treatment plant during the summer when irrigation demands exceed plant flow. This paper provides a case study of the planning, design, and construction of this "two-way" pipeline. Initial project planning included route selection, geotechnical investigation, and aerial survey. The design team investigated pipe material options and, in conjunction with the system hydraulics, determined HDPE to be the most feasible material for the application. The Contractor utilized a state of the art trenching machine that significantly reduced construction time by simultaneously excavating the 6-foot wide trench and laying the fusion welded pipe. Twelve miles of pipeline was installed in 26 working days with the most productive day exceeding 5,000 feet.