Officials in the town of Gilbert, Ariz., knew this wasn't going to be a typical pipeline project. Not when the path has to go through several local, state and federal jurisdictions to get the water delivered. That's one of the reasons the town of Gilbert – which is managing the project jointly funded with the city of Chandler – selected HDR to be the lead designer on a design-build team with Achen Gardener Engineering (AGE) that required the design and installation of more than 13 miles of 48-inch pipeline.
The pipeline is needed to deliver 48 million gallons per day (mgd) of raw water to the new Santan Vista Water Treatment Plant (SVTP). The pipeline will connect to an existing CAP turnout structure near the CAP Canal intersection with Queen Creek Road in Pinal County, and the SWTP is located near the intersection of Higley and Queen Creek Roads.
The project included a corridor route evaluation through multiple state and federal jurisdictions that included preliminary identification of property acquisition needs, public participation and environmental/cultural considerations. A conceptual hydraulic analysis, which included a surge analysis, was also performed by a sub-consultant. This analysis allowed the team to make some key design decisions about air release valves, pipe size and pipe restraint.
One innovative element HDR employed was the development of a detailed matrix to evaluate the alternative corridors for the pipeline. This helped facilitate workshop discussions with the stakeholders to develop a ranking system for the matrix and assign values for the matrix ranking system. Based on the corridor evaluation, consensus for the preferred alignment was reached by all stakeholders.
Because of the aggressive nature of the soils – as a well as several crossings of impressed current gas lines – under HDR's lead our sub-consultants also performed a corrosion control evaluation of the pipeline that was factored in as part of the projects material selection. Based on both construction and project material costs, ductile iron pipe with polywrap was selected for this project.
Throughout the project significant coordination with other projects and developers, as well as with land acquisition needs, was performed, and land acquisition status was monitored. The project design is complete and construction is underway.