American Society of Civil Engineers

Raw Sewage through Steel Pipe: A Unique Application on the Pima County Plant Interconnect

by Jaime Rivera, (Project Manager, Capital Improvements Program Section, Pima County Regional Wastewater Reclamation Department (RWRD), 201 North Stone Ave, 3rd Fl, Tucson, AZ 85701. E-mail:, Chris Lucie, (Supervising Engineer, Brown and Caldwell, 8770 West Bryn Mawr Avenue, Suite 1315, Chicago, IL 60631. E-mail:, Shah Rahman, (Western Regional Engineer, Northwest Pipe Company, 1101 California Avenue, Suite 100, Corona, CA 92881. E-mail:, and William Ast, (Sales Representative, Northwest Pipe Company, 19078 E. Ryan Road, Queen Creek, AZ 85242. E-mail:
Section: Construction, pp. 220-230, (doi:

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Document type: Conference Proceeding Paper
Part of: Pipelines 2010: Climbing New Peaks to Infrastructure Reliability: Renew, Rehab, and Reinvest
Abstract: The Regional Optimization Master Plan (ROMP) is the largest capital improvements program in the history of Pima County Regional Wastewater Reclamation Department (PCRWRD), Arizona, valued at over $720 million in construction, project management and inspection services. One phase of this major undertaking, the ROMP Plant Interconnect Project, consisted of a 5-mile pipeline, with two wash crossings, connecting two metropolitan treatment facilities. Two parallel siphon structures across two wash crossings had to meet more stringent regulatory requirements than the gravity sewer itself. During the Value Engineering stage, welded steel pipe (WSP) was identified as an acceptable material substitution to ductile iron pipe (DIP) for the two siphons. The use of WSP enabled the Owner to meet and/or exceed the performance requirements for strength and corrosion protection of the Arizona State Rule governing the design of sanitary sewers. After reviewing the rigorous testing performed on polyurethane as a dielectric barrier against corrosion, the PCRWRD approved the use of WSP, lined and coated with polyurethane, for the project siphon crossing application. The two parallel steel pipelines were buried at depths of 30 feet, and the use of lap-welded joints provided a fully restrained piping system. A portion of the funding for this project came from the stimulus package provided as part of the American Recovery and Reinvestment Act (ARRA). This paper presents project details, and descriptions of the processes for adopting an alternate pipe material, the justification for selecting WSP over DIP, qualification of the dielectric coating and lining system, and challenges in the design and construction of the deep parallel siphons.

ASCE Subject Headings:
Steel pipes
Wastewater management