Threading a Needle through the City: The City of Frisco’s Stewart Creek North Interceptor Phase 4

The City of Frisco, Texas, has a population of over 220,000 over a 69.1-square mile area. The City’s Stewart Creek interceptor collects wastewater from a 25-square mile sewershed. Phase 4 of the Stewart Creek North Interceptor (SCNI) consists of approximately 15,440 linear feet of existing 10-in. to 24-in. wastewater main roughly parallel to a tributary of Stewart Creek, constructed beginning in 1991 of primarily PVC and vitrified clay pipes. A condition assessment identified various defects throughout the Phase 4 limits, and the City’s Master Plan indicated that the interceptor within Phase 4 is predominantly undersized for build-out conditions. The City contracted with Halff to provide study and design for replacement of Phase 4 of the SCNI. The engineer performed a pre-design sizing and alignment study. The recommended alignment primarily followed the existing alignment, with realignments in some areas to improve constructability and maintenance accessibility and to reduce public impacts. The final design and construction ultimately included 14,870 linear feet of 12-in. to 36-in. replacement interceptor. This paper will discuss this critical project and the various challenges faced throughout design and construction. The project included several challenges. Though not uncommon among similar projects, the project involves bored highway, major roadway, and railroad crossings, multiple creek crossings, coordination with various utilities, and generally narrow construction corridors in several locations. Challenges more unique to this project include construction through land formerly part of a battery recycling plant on which soil contamination has been identified, construction through multiple neighborhood open space areas, and coordination with multiple developers which owned undeveloped land through which the alignment crosses. The coordination with developers resulted in multiple alignment changes late in design due to the developers’ requests during easement acquisition negotiations to better facilitate upcoming developments. Due to the timeline required to obtain easements from 20 private properties, the project was split into two construction packages. Phase 4A, including construction of 9,010 linear feet of 15-in. to 36-in. pipeline, bid in February 2023 and was awarded for a construction contract amount of approximately $8.65 million. Phase 4B, including construction of 5,860 linear feet of 12-in. to 15-in. pipeline, bid in December 2023 and was awarded for a construction contract amount of approximately $4.81 million. Both phases were bid with a base of PVC pipe and lined concrete manholes, with fiberglass pipe for sections of the interceptor 18 in. and larger and polymer concrete manholes as bid alternates. The City elected to incorporate the bid alternates into the construction. The same contractor was awarded both Phase 4A and Phase 4B, and both phases are currently under construction.