Alleviating Block Island’s dependence on expensive oil-fired electricity generation required interconnection to the Rhode Island mainland and to the 30 MW offshore Block Island Wind Farm located approximately 3 miles southeast of the Island.


Energy generated by the turbines is transmitted to the Block Island Substation, and then to the Rhode Island mainland to the Dillon’s Corner Substation, via 34.5 kV submarine cables. These substations not only support the Block Island Wind Farm, but also connect to the bulk electric grid and telecommunications services on the mainland, increasing reliability and decreasing cost of utilities to the island residents. The Block Island and Dillon’s Corner substations both included: 1) new control houses; 2) 35 kV terminal transmission line structures or underground feeder lines; 3) transformers; and 4) ancillary equipment and bus structures. GZA completed the geotechnical borings, laboratory testing, and evaluation of subsurface conditions, and provided the project team with geotechnical and civil consulting support throughout the design development and construction phases. GZA was on site to assess the need for and extent of removal of weak and organic existing site soils, to be replaced with controlled structural fill. Several foundation support systems were used at the substations, including drilled shafts, mat foundations with integrated oil containment systems, and shallow foundations following subgrade improvement. GZA also worked with the project team during construction of a neighboring 5,600 square-foot underground infiltration basin.


Expediting the design construction of these interconnection substations was vital to enhancing the Island’s critical infrastructure, as well as connecting the first utility-scale U.S. offshore wind farm to the bulk electric grid.