Water Infrastructure: HDPE Pipe Rehabilitation for Tucson’s Growing Demand

The 6.8-mile HDPE sliplining installation project redefines pipe replacement standards with minimal environmental impact

Two major recurring themes resonate with the Sahuarita Supply Line job in Tucson, Arizona:

1. The incredible importance of water security - especially in the western United States.

2. The alarming rate of deterioration of the nation's municipal infrastructure.

Whether you embrace them is beside the point - they are both facts.

Southeastern Tucson has been expanding their water facilities in an area known as the Sonoran Corridor. Water has been successfully pulled from aquifers to previously meet the demands of the service area.

Nearly seven miles of 36-inch diameter Class 150 concrete cylinder pipe (CCP) transmission main installed in the 1960s, was used to convey potable water from the Santa Cruz Well Field to the town of Sahuarita, Arizona - which is more than 20 miles south of the heart of Tucson.

Over time, the repairs became more involved as the length of pipe repaired increased due to the lack of non-corroded steel suitable for repair welding. Segments of the Sahuarita Supply Line were also damaged due to stray current effects, resulting in extensive corrosion damage at metallic gas pipeline crossings.

This line was abandoned due to the corrosion and leakage failures that are all too common with that type of piping.

Yes. You read that right.

ABANDONED.

Not repaired. Not rehabilitated. Not replaced. Just abandoned.

Years of use and tax dollars invested to install and repair, and upon expected failure - it is abandoned.

With offices in Phoenix and Tucson, B&F Contracting's Utility Rehabilitation Division is recognized throughout the Southwest as a market leader in full-service rehabilitation of sewer and water mains. Two of their previous jobs in Phoenix involved a process called sliplining.

Sliplining is when a smaller diameter pipe is inserted into the existing host pipe - in this case the dilapidated CCP line. High-density polyethylene (HDPE) piping is the most common material used in sliplining.

The advantages of HDPE when sliplining are numerous and include:

  • Higher flow rates due to the smooth interior. This allows for the smaller diameter pipe retaining, and in some cases improving the flow rate of the existing host pipe.
  • Flexibility. HDPE is pliable, allowing it to meet any subtle twists and turns in the line without fittings. one continuous string of fused HDPE pipe can be fed into the host pipe.
  • Life expectancy. With resistance to chemicals, corrosion, hot soils, and shifting soils due to seismic activities, an HDPE pipeline can be expected to thrive to 100 years or more. In the past there were concerns with HDPE and how it reacted to disinfectants that are placed in potable water. Those concerns are no longer valid, as long as the piping system utilizes PE4710 with a CC3 compound in accordance with AWWA C906-21.
  • Leak Free. No need to abandon this line. When properly fused by certified fusion equipment and technicians, HDPE piping is leak-free.
  • Eco-Friendly. From manufacturing to transport - to installation - to reduced maintenance - to longevity - HDPE is the most environmentally-friendly piping solution.

After a thorough evaluation of four different pipe types, Tucson Water leadership selected HDPE as the most cost-effective and least disruptive technology, in addition to the other listed advantages.

With residential and business growth along the corridor, Tucson Water re-evaluated planned water treatment and conveyance facilities, to provide the most economical method for development of renewable water resources. The ultimate goal was to deliver 10-million gallons per day (MGD) of flow to this section of the city’s water system.

Enlisting HDPE piping solutions leader ISCO, B&F began work on the line rehabilitation, but like any task, it wasn't without obstacles.

Challenges

A key challenge was horizontal deflections at a few segments which required the contractor to manipulate the pipe in order to connect to the next section. The toughness of HDPE pipe allows it to be pushed and manipulated into place with an excavator bucket without damaging the pipe This process is a huge time saver and is not suitable for many other piping choices.

B&F Site Superintendent Gene de la Cerda directed his crews to “prove out” the internal dimension of the failing host pipe with CCTV prior to work starting.

A second challenge was stringing up the larger diameter HDPE pipe in a right of way that was limited by the local geography and narrow right of way widths along the South Nogales Highway.

B&F used the McElroy T-900, which is a stellar machine for pipe fusion of pipe this size. The tracked T-900 not only permits field butt fusion of the 32” HDPE pipe it allows the fusion tech to fuse on the pipe line fittings such as, mechanical joint (MJ) adapters, which is how the HDPE pipe connects to valves and legacy materials.

The versatility of the T-900 fusion machine operated well in various terrains such as the sandy environment found on the jobsite.

A third challenge was the several riverbed washes that the crews had to navigate. These are riverbeds that only carry water on rare occasions, but the action of the flow of the water creates a ravine in some cases. The actual sliplinging was not a challenge, but several times the crews were required to traverse the washes as they pulled in the long pipe strings. The challenges grew with the width of some of the crossings.

A final challenge for the contractor was not related to HDPE pipe or construction.

It was communication with the various entities involved in a pipeline rehabilitation of this magnitude, which included numerous utilities, environmental and historical organizations, transportation departments and land entities. From overhead and underground lines, permits, easements, right-of-ways, construction approvals and crossings, the sheer scope and distance of the project required special attention. With decades of experience navigating these proverbial waters, the challenges were met and conflicts were resolved.

The design engineer on the job, Kevin Miller with Tucson Water selected DR 21 because this line is intended to run as a gravity flow with a potential upgrade to pressure if greater flows are needed. MJ adapters, the standard and recommended restrained connection to legacy materials, were used throughout the project.

During construction, the crews typically fused pipe sections into 500’ – 1000’ lengths when they pulled the HDPE pipe strings into the failing concrete line.

This 6.8-mile project proved to be the least disruptive and most cost-efficient methodology for failed concrete pipe and will serve as a model for other utilities with a desire to address water security and dealing with similar failing infrastructure.

*excerpts and images of this field report have been taken from the Tucson Water Sahuarita Supply Line 32” HDPE DR 21 Slipline Case Study by the Alliance for PE Pipe

SUBSCRIBE TO ISCO UPDATES

ISCO Updates

#subscribe_ISCO_Updates

TOP