Salem Lateral Pipeline Project

This project provided marine construction support to approximately 1.2 miles of a new 12” lateral gas pipeline tapping off an existing 36” gas transmission line in Salem Harbor in support of a new a 674-megawatt natural gas-fired electric generating facility.  Marine construction included support of horizontal direct drilling, a temporary cofferdam to support confined subsea excavation, a subsea hot-tap of a live 36” gas pipeline, installation of subsea access vaults, protective measures for the installed hot-tap, engineered backfilling, and environmental mitigation.  All work executed in a highly sensitive marine environment with a 9’ tide fluctuation with high currents and extensive commercial and recreational vessel traffic. 


  • Cashman’s role in the project included the design and execution of all excavation, pipeline installation support (via horizontal direct drill), hot-tapping, spool installations, tie-in protective measures, and backfilling, including all required support of excavation and environmental control measures.
  • Cashman designed and installed an 85’ x 55’ cofferdam, straddling the existing & in-use gas pipeline, with entry and exit windows for the lateral pipeline and to allow water to freely flow (during tidal cycles) while containing suspended sediments during construction activities. 
  • Approximately 1,500 cubic yards of sediment were carefully excavated from within the cofferdam and around the existing pipeline, and placed in hopper barges for temporary storage/decanting.
  • Cashman provided all marine elements in support of the horizontal direct drilling of the new lateral pipeline/hot tap location to shore.
  • Cashman, via subcontracted diving services, successfully executed the hot-tap, tie-in spool fabrication and installations, and installation of the protective concrete vault.
  • Cashman then extracted the cofferdam/support of excavation measures and returned the seafloor to its previous natural state with the pipeline tie-in assembly safety buried below 6’ of cover.
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Spectra Energy / Algonquin Gas
$12.54 million
May - November 2016