Greg Scoby, PE
# 2021 Amsterdam
This paper will detail the steps taken during adoption of HDPE for potable water systems improvements including material justification, creation of related specifications, investigation of available piping components, qualification of contractors and the construction/inspection of related systems.
The City of Palo Alto, California, USA adopted HDPE as the primary material for water distribution in 2010. This adoption was implemented in an accelerated water main replacement program initiated in 1994. The accelerated infrastructure program lowered the level of replacement from 233 years to 77.6 years which is well within the anticipated useful life of HDPE materials (100 years minimum). This paper provides a historical account of the City’s Utilities Department along with statistics of the systems composition. Several construction projects involving the exclusive use of HDPE are included.
Approximately 10 years ago, the City of Palo Alto made the decision to convert to HDPE for potable water distribution. This decision was based on the experience gained with the exclusive use of polyethylene for natural gas distribution made in the late 1980s. Several factors were considered to support this conversion. The major driving force was the leak free performance of a monolithic self-restraining system provided by fused connections. Other factors guiding this decision included the projected life of the material, minimizing corrosion failure associated with buried metallic components, ability to install piping with trenchless construction methods to minimize installed cost and customer inconvenience and the need to construct a resilient distribution system capable of remaining in service during and after seismic events. The San Andreas Fault traverses Palo Alto. In the early 1990s, utility department staff convinced Council members of the need to increase replacement levels associated with the water, gas and wastewater systems. An accelerated infrastructure replacement program was funded and additional engineering staff hired to focus on the design and construction of all three mentioned systems. In 2009, staff started the revisions of the existing standards Copyright © 2021 by (Greg Scoby, PE, Crossbore Consultants, Gregs@CrossboreConsultants.com)and construction documents for the water system and joined the Plastics Pipe Institute Municipal Advisory Board and the American Water Works 263 Polyolefin Committee (responsible for polyethylene standards) to ensure the newly created HDPE specifications represented the best practices.
Staff utilized past experience gained during natural gas projects to implement the use of trenchless construction methods for potable water system replacement. The first HDPE project, Water Main Replacement 21/22, was constructed over the 2010/2011 fiscal year with main sizes ranging from 8 inch (200 mm) through 16 inch (400 mm) encompassing a total 31,680 linear feet (9.7 km) of mains. Construction was performed by a polyethylene qualified contractor utilizing both trenchless and open cut construction methods. Based on the success of this project, full adoption of HDPE for water, including mains and services, was made for all system extensions and improvements/replacements. HDPE is currently the primary material specified by the City for potable water distribution.