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PWSA’s Trenchless Success Drives Reliability Mission

The Pittsburgh Water and Sewer Authority (PWSA) is using state-of-the-art renewal systems to upgrade its existing water system pipeline infrastructure, and extending the life of these assets by 50 years.

Utilizing trenchless technologies and a best practices collaborative approach allowed PWSA to minimize disruption not only for its citizens, but also the inhabitants of the Pittsburgh Zoo & Aquarium.

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Officially established in 1984, PWSA currently oversees a $185 million capital improvement program (CIP), however PWSA’s roots trace back much further, to 1802 when Pittsburgh was a municipality of 1,600 people. Over the next two centuries, Pittsburgh’s population grew and so did its water needs. But as its population and water needs grew, its water infrastructure continued to deteriorate.

In 2019, PWSA established the Water Reliability Plan (WRP), a series of once-in-a-generation capital projects that will renew key components of PWSA’s water production and distribution system. The WRP was developed in response to growing concerns about the lack of redundancy and resiliency in the water system that would prevent the Authority from completing the critical replacement of the 112-year-old Clearwell at the Pittsburgh Water Treatment Plant.

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The WRP is a $470 million multi-faceted program, which includes rehabilitation and replacement of water pump stations, rehabilitations of critical transmission mains (including Rising Mains 3 and 4), and renewals of potable water reservoirs that will culminate with the replacement of the existing Clearwell. The WRP, anticipated to be completed by 2032, will restore the resiliency and reliability of the drinking water system of the City of Pittsburgh that can be relied upon for many years to come.

Preparing pipeline joints for renewal.

Delivering reliable water service to the citizens of Pittsburgh is a mission of PWSA’s and the WRP creates focus and investment toward critical assets. For this goal to be accomplished, analysis showed that a series of upgrades across the water treatment plant, storage reservoirs and pumping stations needed to occur, along with addressing transmission mains that convey water between the pump stations and reservoirs.

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Rising Main 3 (RM3) and 4 (RM4) are essential components of PWSA’s water supply system, and a key aspect of PWSA’s ability to deliver reliable water service. Their condition directly impacts the overall system performance. RM3 and RM4 run parallel and connect the Bruecken Pump Station to the Highland Reservoir No. 2, which holds water prior to supplying the distribution grid.

RM 4 runs for 6,500 lf from the Bruecken Pump Station to Highland Reservoir No. 2. Comprised of both a 50-in. diameter riveted steel section (installed in 1939) and a 48-in. diameter prestressed concrete cylinder pipe (PCCP, installed in 1972), RM4 presented unique challenges. Its urban location included passage beneath an active railroad, a state highway, and the Pittsburgh Zoo & Aquarium.

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The pipeline’s steep terrain and limited accessibility further complicated matters. While some segments had undergone prior inspection, others remained uncharted territory. In light of these constraints, including unknowns, the design team recommended the use of carbon fiber-reinforced polymer (CFRP) for RM4’s renewal. This specification was due to the low impact, flexibility, and versatility of CFRP as a fully structural renewal liner.

Outreach to unique site visitors.

CFRP is a robust and dependable pipeline renewal technology, first used in civil infrastructure repair in the 1980s. Comprising multiple layers meticulously applied within large-diameter pipelines, this composite material offers a game-changing advantage: pipeline renewal without excavation.

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The system’s layered installation allows dynamic adjustments throughout the pipeline alignment and accommodating to varying loading criteria. Moreover, CFRP’s versatility extends to renewing multiple non-continuous segments, precisely targeting the most degraded areas. Remarkably, the final cured system measures a mere half-inch in thickness — a stark contrast to other AWWA Class IV renewal methods. This profile ensures minimal hydraulic capacity reduction, making CFRP the discerning choice for renewing critical pipelines like RM4.

The CFRP installation process.

The renewal of RM4 was awarded to Structural Preservation Systems LLC (STRUCTURAL) through a traditional Design-Bid-Build project delivery method. However, the subterranean environment posed numerous unknowns—typical of buried utilities that are often “out of sight, out of mind.”

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Successful project delivery, when working with the complexities of underground infrastructure, hinges on collaboration and adaptability to respond to as-found conditions. When challenges arose during construction, the project team engaged with the designer and owner to ensure alignment with the owner’s objectives.

STRUCTURAL’s expertise in collaborative delivery proved pivotal. The team fostered open lines of communication and regular discussions among the owner, designer and builder allowed emerging issues to be addressed swiftly. In order to maintain an accurate accounting of design changes, variations from the original design were meticulously documented.

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In addition to the overall alignment among the team consisting of the owner, designer, and builder, STRUCTURAL continued the collaborative approach with multiple subcontractors to bring the project to fruition.

STRUCTURAL, as the prime contractor, renewed approximately 2,600 lf of pipe using CFRP, while its subcontractor partners performed complementary scopes: traditional open cut and replacement (pipeline and air valve replacement); CFRP system design by Simpson Gumpertz and Heger, an expert in pipeline renewal with CFRP; traffic control; electromagnetic inspection of previously uninspected pipe using Pure Technologies; and disinfection of the transmission main before bringing it back online. This collaborative approach fostered cohesion among the owner, designer, and builder, ensuring the project’s successful completion.

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Pipeline renewal completed using CFRP.

The collaborative efforts of the team have woven innovation and foresight into PWSA’s program. The designer’s forward-thinking accounted not only for the immediate pipeline renewal, but also anticipated future system upgrades.

Amidst urban complexities, the use of CFRP emerged as a game-changer. This light weight, low profile, and robust material allowed targeted renewal without excavation. The team brought RM4 back to life — a milestone in PWSA’s commitment to reliable water supply.

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Barry King, P.E, PMP, is director of engineering and construction at Pittsburgh Water and Sewer Authority. Paul Mourt is principal project manager at HDR.

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