Donovan Avenue Water Main Phases 1 and 2
City of Bellingham
Water, Transportation, Stormwater, Environmental
The existing 16-inch diameter water main along Donovan Avenue in Bellingham was experiencing multiple and severe water main breaks due to excessive system pressure (exceeding 200 psi) and deteriorating pipe material. The water main breaks resulted in massive service disruptions and significant flooding of low-lying properties. The City of Bellingham hired RH2 to design both a short-term solution to the pipe breaking issues through water main replacement and a long-range plan to reduce the excessive pressures in the Fairhaven and Edgemoor Neighborhoods through pressure zone reconfigurations and creation of a new pressure zone.
Phase 1 consisted of RH2 providing expert water system modeling and system planning to create a new 360 Pressure Zone for the City to balance and reduce high system pressures. The result was a report documenting a three-stage plan with project phasing that allows the City the flexibility to implement the plan over time and at the pace that fits the City’s availability and budget. We developed sequencing plans and standard connection details to assist the City crews with implementation.
Phase 1 also consisted of RH2 designing water main replacement of the aged, unlined cast iron pipe that had corroded to the point of failure at the low point in the system. RH2 worked an accelerated design and permitting schedule to meet the City’s need for construction in the summer of 2018. We designed the replacement of 4,500 LF of water main with new 16-inch ductile iron pipe, and worked closely with City crews to design water main connections and thrust restraint that would allow the City to immediately restore service following connections. We also developed custom reverse thrust blocking details for the City that can be re-used in their standards.
The Phase 2 design was completed in early 2020 and purposefully bid in spring 2020 to stimulate the local Bellingham economy during the pandemic. This phase included 3,700 LF of water main and presented multiple design challenges with crossings under I-5 and under Connolly Creek. Through careful analysis and data review, RH2 concluded that the water main under I-5 did not require immediate replacement because the pipe had a protective lining, and a casing pipe exists to allow future replacement, if required. This saved the City significant project costs. The crossing under Connolly Creek was permitted through WDFW for a Hydraulic Project Approval and RH2 designed a jacked pipe casing, which provides replacement flexibility to future City generations, if needed.
Additionally, because the City was familiar with RH2’s stormwater expertise, they supplemented our contract scope to incorporate the replacement of 24-inch storm pipe in Donovan Avenue west of I-5 and pavement drainage design with catch basins east of I-5. RH2 carefully considered the 24-inch pipe outfall to Connolly Creek and effectively guided the City for efficient permitting efforts. All phases of this project were completed on time and under budget.