Underground Solutions Project Profile: HDD Installation

October 10, 2017 by NASTT Staff



HDD provides a rapid and reliable way to replace aging steel pipeline

The City of Santa Cruz Water Department (SCWD) has long anticipated the need to assess, design and build a new pipeline system as part of the existing North Coast System (NCS) which delivers raw water to their water treatment plant. The existing NCS is a series of stream diversion structures and collection
conduits and includes approximately 16 miles of pipelines that are nearing, or have exceeded, their design life and must be replaced. The replacement pipeline is a series of phased projects and will provide a water delivery system that will be reliable for the next fifty years or more.

Phase 3 of the overall initiative included the replacement of 18,600 feet of primarily 24-inch diameter pipe using open cut methodology. Additionally, five trenchless crossings, one horizontal directional drill (HDD) crossing under sensitive environmental habitats and four horizontal auger bores crossing under California Department of Transportation and railroad right-of-ways were included in Phase 3.

In 2015, this phase of the NCS project had been designed but had not gone out to bid when a failure of a 1,200-foot critical section of the existing steel pipeline at the Lombardi Creek Crossing location prompted SCWD to schedule that section for immediate replacement. Site conditions at this location required replacing the pipeline using HDD installation methodology. Its location within the Wilder Ranch State Park elevated environmental concerns because the park has strong biological, scenic, cultural and recreational values.

The replacement of the Lombardi Creek crossing began in late 2015 after selecting the HDD Company from Granite Bay, California to be the contractor. The actual drill alignment length was approximately 1,300 feet with an elevation change of approximately 60 feet. Entry and exit angles were approximately 10 degrees. The final alignment was 25 feet below the bottom of the creek. 24-inch DR 18 Fusible PVC®
pipe was selected as the replacement pipe. Overall, the drill alignment and bore preparation took four weeks. While the bore hole was being drilled and reamed, the Fusible PVC® pipe was fused by Underground Solutions. Once the bore hole was prepared, the Fusible PVC® pipe was pulled into place,
a process that took approximately 8 hours. The replacement project took two months from mobilization to pressure test and the replacement pipe was placed into service after completion. This new segment will be tied into the new NCS Phase 3 pipeline when it is complete.

Project Manager Kevin Crossly stated, “The Lombardi Gulch HDD Undercrossing is the largest and longest installation of Fusible PVC® pipe to date for the City of Santa Cruz. The City was very pleased during all phases of the project with Underground Solutions which provided technical support solutions during design of the project. When the City experienced the 0.5 MGD leak and fast tracked the construction phase, Underground Solutions was responsive to the project requirements to secure, fabricate, deliver and fuse the 1,300 LF of pipe that was ultimately installed on a very aggressive schedule of approximately eight weeks. Fusible PVC® pipe is a great product that Underground Solutions will support and stand behind. We will definitely consider using Fusible PVC® pipe on future projects.”

Underground Solutions, Inc.