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In September, Viewpoint, a Trimble Company and construction management software leader, announced the winners of their 2019 Viewpoint Construction Awards at the Collaborate Viewpoint User Conference. The three categories of the awards featured the most collaborative, most challenging, and most innovative projects of the year. Caldwell Marine International proudly won the Most Challenging Project award for the HEEC Submarine Cable Replacement project in the Boston Harbor!

The Dear Island Waste Water Treatment Plant Project

In April of 2018, Caldwell Marine International (CMI) was awarded an EPC contract to replace an existing 115 kV submarine cable system across the Boston harbor.  The owner operates an existing submarine cable extending from South Boston to the Deer Island wastewater treatment plant, and the cable had to be removed and relocated to accommodate the deepening of Boston Harbor (which the city of Boston is working on to accommodate larger shipping and cruise ships to expand their capabilities).   The goal of the project was to install a new cable system from South Boston to the Deer Island wastewater treatment plant, ready for energization by July of 2019 and remove the old cable by the first quarter of 2020.

The new cable system includes 8,700’ of land cable installed through duct banks and vaults in South Boston, transitioning to 15,400’ of submarine cable under the main shipping channel and across Boston Harbor, then back to a 1,350’ land cable on Deer Island where it would to be connected into the Deer Island power system.

Caldwell mobilized crews to Boston in June 2018 to test run the cable plow, proving the cable route and verifying it was possible to achieve the required 10’ depth of burial.  Once the cable route was confirmed, the submarine cable was released for manufacture.  Produced in Prysmian’s factory in Italy, cable production and delivery took approximately 6 Months.

What Made This Project So Difficult

In September 2018, Caldwell Marine International was awarded a change to the original cable contract to instead install the shore approach conduits via Horizontal Directional Drilling (HDD).  Partnering with our sister company, ECI Drilling International, the first HDD, was designed to extend from inside Conley Terminal on the South Boston side, under the main shipping channel, and exit in close proximity to existing eel grass beds in Boston harbor.  The second conduit was designed to be drilled from inside of the Deer Island waste water treatment plant, extend under public park areas, and exit in the shallows of Boston Harbor.

Caldwell worked with ECI Drilling International to mobilize two complete HDD spreads with full marine support in order to drill both HDD’s simultaneously.  Work was started in mid-October 2018 and immediately both drilling crews encountered extensive differing site conditions which delayed drilling approximately 90 days.  Caldwell and ECI worked hand in hand with the owner and their engineers to redesign both HDD’s. Work hours were extended, and crews worked 24 hours per day, 7 days a week from mid-November until early March.  CMI and ECI were able to recover most of the schedule time and both conduits were installed by early March 2019 ready for the submarine cable.

Simultaneous with the HDD work, Caldwell mobilized a 180’x60’ cable installation barge, equipped with a 600-ton cable carrousel.  In mid-February, Caldwell trans-loaded 16,400’ of submarine cable from a transport ship onto the installation barge and then towed the barge from our Staten Island, NY yard to Boston Harbor.  Over a two-week period, Caldwell installed the cable successfully connecting South Boston to Deer Island.

Arriving on site in early April, Prysmian Cable furnished and installed the land Cable pulling, splicing and testing over 10,000’ of cable, completing the cable installation on July 3rd 2019.  Despite a shortened construction schedule, winter weather, differing site conditions and numerous design changes, Caldwell Marine, ECI Drilling International & Prysmian Cable delivered the new cable system on time.

Caldwell returned to Boston in November 2019 to remove the original submarine cable and completed the final phase of the project.  The removal required close coordination with the captain of the port, Massport, US Army Corps of Engineers and Logan Airport to remove the old cable without interfering with airport operations or shipping traffic.

Here is a closer look at our Boston submarine cable installation project:

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