Suffolk County is planning to build a replacement outfall pipeline with a 4.6 km (2.8 mile) 3.3 m (10.8 ft) internal diameter soft ground tunnel. The Owner and designer had to consider significant regulatory and permitting requirements, maintaining the existing outfall during construction of the outfall replacement, potential risk issues, ground conditions and community acceptance during design. Major decisions included selecting the TBM method (slurry versus earth pressure balance machine), use of ground freezing versus secant piles for shaft construction, GBR baseline values, potentially variable ground conditions and working in and around environmentally sensitive areas. This project is expected to bid and be awarded in early 2017.
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