HDD Bundled Water and Sewer Pipelines Beneath the Napa River: Facilitating Build-out in the Northern California Wine Country

摘要

Stanly Ranch is located a half-mile west of the Napa Sanitation District’s Soscol Water Treatment and RecyclingrnFacility in the Northern California wine country near Napa. Despite its close proximity, the ranch has no sanitaryrnsewer and recycled water conveyance pipelines to and from the facility. Between the ranch and the facility are railroadrntracks, an extrapolation of the West Napa fault, the Napa River and broad wetlands. Plans for the ranch include a fivestarrnSt. Regis resort. Resort development requires providing sanitary sewer and irrigation water services to the ranchrnfrom across the Napa River. Geotechnical findings led to the horizontal directionally drilled (HDD) design andrnconstruction of an 8-inch-diameter (205 mm) sanitary sewer force main and a 24-inch-diameter (610 mm) recycledrnwater pipeline (both of high density polyethylene) between the ranch and the facility. The pipelines were bundled andrninstalled together in one 2,300-foot-long (701 m) continuous HDD reach. Key geotechnical findings that led to thernselection of HDD as the preferred trenchless method of installation are illustrated. The HDD design is summarized,rnincluding estimates of pipe stress during pull-back and hydrofracture risk. Details and events of the actual HDDrnconstruction are compared with design estimates.