This project will consist of the installation of a new 14-inch interior diameter pipeline underneath the Mad River via horizontal directional drilling (HDD). The replacement pipe material will either be High Density Polyethylene (HDPE, 18-inch outside diameter) or Fusible Polyvinyl Chloride (FPVC, 15.3-inch outside diameter). This new pipeline will replace the existing 14-inch water main currently located on a railroad trestle that is aging and becoming undermined, and will continue water service to the communities of Blue Lake, Fieldbrook, and Glendale. The pipeline will tie-in to the existing 14-inch transmission main on the west side of the river, east of Warren Creek Road and on the east side of the river, just west of Glendale Drive.
HDD is a trenchless construction method in which a pipe is installed along an arcing drill path, beginning and ending at entry and exit pits, respectively, and passing under the Mad River. A drill rig is set up on the entry side (in this case the west side of the river) and drills a pilot bore to the exit point. The pilot bore is then reamed in one or more passes to the size required for pullback of the prefabricated pipe string. After reaming is complete, the pipe is pulled into the bore, preferably in one continuous operation. The pilot bore will be installed from the west side of the river and an entrance pit will be constructed on a District-owned parcel, approximately 90 feet east of Warren Creek Road, 600 feet north of the intersection with Burlwood Lane. The drilling bore will terminate on the east side of the river, just southwest of Glendale Drive on the property of GR Sundberg, and an exit pit will be constructed at this location. The new pipe will be assembled (fused) and laid out on the Sundberg property, which should allow the pipe to be pulled back in one continuous pull.
A bentonite(clay)-based drilling fluid is used in the HDD process to aid in excavation of the soil, carry the cuttings from the bit back to the drill rig, provide hydrostatic support to the otherwise unsupported borehole, and to cool and lubricate the drill pipe and tooling during drilling. The returned drilling fluid is sent through a solids separation plant with a system of vibrating screens and hydrocyclones that remove the majority of the soil from the slurry. Clean drilling fluid is sent back to the bit. Drilling fluid recovery pits are commonly excavated at each end of the bore. The pits are usually 3-6 feet wide, 6-12 feet long, and 2-4 feet deep. The risk of inadvertent fluid leaks is an important consideration for HDD projects. This typically occurs when excess drilling fluid pressures cause fluid to escape the bore and surface through granular soils, cracks in cohesive soils, or along other natural or man-made conduits. Drilling fluid is generally a non-toxic mixture of water and bentonite clay; however, spills are viewed as an environmental risk, and this project will be closely monitored during drilling to prevent such leaks.