The first major US offshore wind farm, planned for the Massachusetts coast, has reached a key permitting milestone with the release of a long-awaited federal environmental study that considers the project’s impacts on fisheries and navigation. The project has experienced delays over concerns that its wind turbines will hurt commercial fishing. The 800-megawatt Vineyard Wind is expected to generate enough power for more than 400,000 homes in Massachusetts. The lease area is located 15 miles off the coast of Martha’s Vineyard.