Suffolk County executive Steve Bellone said they expect a 12-month excavation, with the entire project completed by August 21.”This morning I will be unveiling ‘Colleen’, the tunnel boring machine that will dig beneath the floor of the Great South Bay as part of the Cross-Bay Outfall Replacement Project,” he said on Twitter. “This is the largest infrastructure project of its kind in county history.”

The Outfall Replacement project will replace a 2.6-mile portion of a 72in outfall tunnel from the Bergen Point Wastewater Treatment Plant to the Jones Beach barrier island.

Suffolk County Department of Public Works owns and operates the Bergen Point Wastewater Treatment Plant in Babylon, New York. Gall Zeidler Consultants provided consulting to the study team by performing preliminary technical review of the geotechnical data collected during the first phase of the boring program and participated in the alternative selection review.

The replacement tunnel is planned to be approximately 14,200ft (4,330m) long from launch shaft to receiving shaft, connecting Suffolk County’s Sewer District No.3–Southwest Bergen Point Wastewater Treatment Plant under the Great South Bay, to the Barrier Island.

According to Gall Zeidler this size was established based on the need for efficient tunnelling for 14,200 linear feet and on installation of the carrier pipe. Ground conditions include sediments over metamorphic bedrock, upper glacial, boulder/cobble till moraines, Gardiners clay, marine sand and clays, deposits of clay, silt, sand and gravel, clay Deposits and sand.

OHL has a USD 187M joint venture contract (40% OHL USA, Inc., 40% Posillico Civil, Inc., 20% SELI Overseas USA, Inc.) for the project. The JV said it selected a Herrenknecht slurry TBM as the most effective and efficient means of tunnel excavation and elected to use 48-inch wide precast segment liners.