The city of Largo, Florida, with of approximately 85,000 residents, recently completed a $38 million wastewater collection system improvements project to eliminate sanitary sewer overflows (SSOs) that had regularly occurred following significant rain events. This Wet Weather Monitoring and Pumping System Project, involved construction of approximately 14.2 miles of sanitary force mains and the reconstruction and upgrade of seven pump stations. Following prequalifications and value engineering negotiations with the selected contractor, the project was awarded in early 2015 and placed into service in late 2016. One of the key challenges facing this project was the construction of a new force main traversing the city from east to west through urban and residential rights-of-way with dense utilities and multiple roadway and waterway crossings. Force main piping ranged from 12-inch to 30-inch diameter, of ductile iron and polyvinyl chloride construction, with installation by open cut, horizontal directional drilling (HDD), and jack and boring. Necessitated by wetlands and Florida Department of Transportation (FDOT) road crossings, roadway and driveway impacts, residential encroachment onto easements, and crowded utility/drainage corridors, twenty-five (25) separate HDDs were included in the pipeline route, totaling 5.6 miles of the pipeline—using fused polyvinyl chloride pipe (FPVCP). Drill design was based on pipe material selection, entry and exit location availability, layout and pullback requirements, bore path tracking capabilities, and geotechnical conditions. Details of individual drills are discussed, as well as significant issues experienced during construction, such as frac-outs, drilling mud management, and bore path tracking. The incorporation of trenchless methodologies such as horizontal directional drilling and jack and boring allowed the project to be completed successfully, with significantly less impact to the community and environment than open-cut options. The final product will reduce sanitary sewer overflows in the city of Largo for many years to come.
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