System Reliability Improved through Directional Drilling in Fast Track Force Main Replacement
Kishen Prathivadi
Kishen Prathivadi, Timothy Monahan, Nina Mao
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The Sewer Authority Mid-Coastside (SAM) transports and treats wastewater from several coastal communities in San Mateo County, California. In the spring of 2017, one of SAM’s force mains, the Granada Force Main, experienced a series of ruptures that disrupted operations and negatively impacted local beaches. Due to its previous history of breaks, its age, and materials of construction, SAM initiated a program to replace most of the force main to improve system reliability, protect residents, and safeguard the coastal environment.

This challenging project was executed on a short schedule and a limited budget. SAM expedited the design process in parallel with surveying, condition assessment, biological assessment, wetlands delineation, and permitting. The design incorporated durable corrosion resistant materials such as high-density polyethylene (HDPE) pipe and appurtenances and unique construction techniques such as horizontal directional drilling to accelerate the construction process.

The new force main was commissioned in March 2018, less than a year after the initial break in 2017. SAM successfully executed survey, design, obtained required permits, and constructed a new 5,700 linear foot force main in under eleven months at a cost of $2.0 million. The efficient execution of this project is based on simultaneous execution multiple task and collaboration with all parties. This collaboration resulted in an efficient construction process with change orders totalling less than one percent of the construction contract amount.

Additionally, SAM’s power consumption at Portola Pump Station has been noticeably reduced due to the improved hydraulic capacity of the HDPE pipe material and the lowered static head of the new force main. The new force main has an expected service life of over 100 years which greatly improves the system’s reliability.

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