Rainbow Municipal Water District Brings New Life to Failed 24" Steel Waterline with Fusible PVC® Slipline

During heavy rains in December of 2009, the levels of the Rainbow Municipal Water District's 50 million gallon Morrow Reservoir began to fall for no obvious reason. The source of the water loss was eventually traced to the District's 24 inch "Line Q3", a 300 psi epoxy coated, welded steel, bi-directional pipeline.

The Rainbow MWD is located in Northeast San Diego County and services both agricultural and residential customers in portions of Fallbrook, Pala, and Bonsall. Designed to carry approximately 9.4MGD of water at 300psi, the District installed "Line Q3" beneath the San Luis Rey River in 1995 by horizontal directional drill (HDD). In addition to providing residential and agricultural water, "Line Q3" is also a critical component of the region's firefighting infrastructure.

Pipeline Details and Project Summary
Project: Rainbow Municipal Water District Line Q3 Project - Slipline Rehabilitation
Location: Fallbrook, CA
Length: 2,000 LF
Pipe Size: 16" DR14
Pressure Test: 355 psi for five hours
Installation: Slipline
Owner: Rainbow Municipal Water District
Engineer: JC Heden & Associates / Brierley Associates
Contractor: Golden State Boring & Pipe Jacking

Subsequent CCTV of "Line Q3" showed that it was filled with a large amount of sand and sediment from the soils surrounding the pipe, an indication that the pipe had been compromised by some type of break.

The District tasked the engineering team of JC Heden & Assoc. and consultant, Brierley Associates, with finding a solution to repair the failed pipeline.

To accomplish this task, the project was divided into several phases:

  1. Remove the sediment that had built-up over time.
  2. Mandrel test the line to ensure the sediment had been removed and the line had not collapsed.
  3. Slipline a new, fully pressure-capable carrier pipeline inside the failed 24" welded steel line.
  4. Pressure test the new line.
  5. Grout the new line in place.
  6. Reconnect the line and return it to service.

In September 2010, Golden State Boring & Pipe Jacking was selected to perform the clean-out, mandrel test, installation, pressure test, and reconnection of the new pipeline. In order to achieve the required flow and pressure capacity, the District turned to Underground Solutions Fusible PVC® pipe as the replacement pipe. Per Jeff Heden of JC Heden & Associates, "Of the various pipe materials evaluated for this project, only Underground Solutions 16" DR14 Fusible C-905® pipe was capable of providing a pressure class of 305 psi with a large enough ID to meet the required flow of the system."

To remove the sediment from the failed 24" line, Golden State utilized an HDD rig outfitted with a custom fabricated opentopped bucket/spade at the head. The drill fed the bucket forward into the steel line and pushed into the sediment. Once sufficient resistance was realized, the bucket was extracted, closing a trap door located in the front, and trapping and removing the sediment from the pipe. This process took approximately one week to complete. When finished, approximately four cubic yards of material were removed from the line. Once the sediment had been cleared, a mandrel was run through the line several times to confirm the line was clean and free from obstructions. In early October, while the line was being cleaned and mandrel tested, an Underground Solutions' Fusion Technician was onsite fusing the Fusible PVC® pipe for installation. Due to space constraints, there was only enough room to lay out approximately 500 LF of pipe. As a result, the pipe was fused in four separate sections, ultimately requiring three intermediate fusion joints to be completed during pull-in.

To ensure that the new pipeline would be completely grouted in place, four 2" grout lines of various lengths were strapped to the new 16" Fusible PVC® pipe during the pull-in phase of the project. After the pipe and grout lines were in place, the new line was successfully pressure tested at 355 psi for five hours. Once the pressure test was completed, pressure gauges were installed on the end caps at each end of the pipeline and the new pipe remained pressurized to 100 psi. This was done to monitor the external forces imposed on the new pipeline during the grouting procedure. Once the grouting phase was complete, the line was reconnected and returned to service in mid-November.

Billy McCoy, Project Superintendent for Golden State Boring and Pipe Jacking, states: "We have completed several jobs with Underground Solutions and they deliver a high quality product every time, with field support to match."



Custom Fabricated Cleanout Bucket


Trapdoor


Sediment Removal


Bucket Laden w/ Sediment


16" Pullhead


High Pressure End Cap for Pressure Testing


Pipe Staging, Fusion, and Layout Area


Pipe Fusion


Work Area After Demobilization & Hydroseeding