Design Build Solutions for Wastewater Collection Systems and Treatment Facilities. Gulf Coast Underground, LLC, is a full service general construction and engineering firm. One major component of our business is to investigate and evaluate the condition of municipal infrastructure, while another is to provide the latest technologies available to rehabilitate or replace the system. Our in house Design-Build capabilities truly set us apart from our competition. Since 2003, GCU has provided honest and dependable, long-term solutions across Florida, Alabama, Mississippi, Louisiana, Georgia, Tennessee, Texas, North Carolina, South Carolina, Virginia and Arkansas. From the outset, GCU was built upon relationships and our top priority has been and will continue to be to serve our clients with professionalism, provide them with cost and time saving solutions, and prove ourselves to be a trusted technical resource.