Gulf Power installed four electrical power distribution subaqueous cables across the Sound as an upgrade and replacement to existing cables. Kleinfelder provided horizontal directional drilling (HDD) design support and assisted the client with avoiding impacts to sensitive environmental resources and streamlining permitting.
Typically, cables are installed via a jet plow which, in this case, would result in both direct and secondary impacts to seagrass in the project area. Impacting approximately 2 acres of seagrass would require regulatory approval (1-2 years), mitigation of the impact ($800,000), and a 10-year bond for the long-term costs of monitoring the mitigation. Due to the width of the Sound, the cables could not be strung through a full HDD bore.
Kleinfelder designed a combination of drilling methods to install the cables. Boring 1,000 ft. under existing seagrass and pushing HDD pipe from landside in one direction mitigated environmental impacts. Cofferdams that could withstand wave and wind energy were designed within the Sound as workspaces to dig down to the pipe and install the cable. To tie in the cable, drilling to the pipe was performed from a barge. Conventional jet plow was utilized from the intersection to cross the center of the Sound. All work was completed under an ACOE Nationwide Permit and FDEP General Permit.
Kleinfelder’s approach mitigated environmental impacts by avoiding near-shore seagrass and reduced the permitting timeline by at least a year through the use of a general permit. By eliminating the need for long-term permitting, monitoring, and mitigation, Kleinfelder reduced operating costs, saving Gulf Power more than $500,000.