Following the assessment, WSP evaluated various alternatives for immediate replacement of the pipelines and completed the design and permitting of two new high-density polyethylene (HDPE) replacement pipelines. Using the float-and-sink approach, the replacement pipelines were installed in a shallow trench dug 6,000 feet across the harbor, offset from the existing active pressure mains to protect these deteriorated pipes. Because the existing mains had no redundancy, a 6,000-foot temporary bypass was installed and connected to the upstream sewer and treatment plant before the permanent connection of the new mains to the system was made.
Design innovations included careful selection of materials to provide long service life in a corrosive marine environment, as well as provisions to monitor and protect the environment and public safety throughout construction in this historic and popular recreational harbor. Construction was completed with no adverse environmental impact, as demonstrated by monitoring of sensitive resources, and included restoration at the Marblehead and Salem shorelines to protect a recreational beach and reconstruct a seawall. The new pipes provide improve capacity and redundancy, and are expected to provide service for well over 50 years.