Surface Impoundment Closure

Phillips Contribution

Phillips was awarded the contract for this work in mid-February 2023 with an immediate start date of March 2023 to complete dumucking ahead of the September 2023 scheduled outage date for structure replacement. Pre-construction planning for safety, environmental considerations, and quality was a high priority due to construction operations on water utilizing dredges mounted on barges, amphibious excavators, boats, etc. As part of pre-construction, Phillips used a bathymetric survey to map the muck elevation at the bottom of each canal and hand probing to map the rock elevation under the muck. These detailed pre-construction evaluations allowed for the use of floating turbidity barriers at the mouth of each canal. A dedicated Phillips Environmental Project Engineer performed daily assessments of BMPs, and Phillips coordinated with FPL’s environmental rep and SFWMD during the pre-construction, production, and post-construction phases of work to ensure compliance.  

During construction, dredge-mounted barge excavators were the primary demucking tool, with amphibious excavators assisting in limited access areas. This allowed for the safest option to limit the crew size on barges, boats, and the ground. It also was the best option to optimize demucking production to meet FPL’s schedule. Phillips implemented GPS with the excavators to allow for fixed dredging elevation to the target demuck elevation requested by FPL above the rock level and selected dredge head equipment for vegetative cutting heads instead of rock heads. 

Phillips’ front-end equipment selection maximized both safety and production elements. Dredge selection allowed for a higher production ceiling, and field crews executed the work efficiently ahead of the initially planned production schedule. 

The demucking scope was completed by Phillips in mid-September 2023 with zero safety incidents, zero environmental issues, on schedule, within budget, and to the target demucking elevations requested by FPL. The structure replacement for Phase C went underway with adequate canal water depths that allowed FPL’s contractor to access the work areas without issue. This operation was critical for FPL’s transmission operations as the structure replacement increased storm resiliency to this transmission corridor for customers throughout South Florida. This region faces frequent hurricane impacts and has unique access constraints that would have otherwise presented challenges with FPL repairing an older 500kV structure damaged by storm impacts. 

CHALLENGES & SOLUTIONS  

The bathymetric survey was attempted for post-construction of as-builts, but this attempt encountered challenges with the rainy season in Florida, and demucking operations created cloudy water conditions that interfered with the survey’s analysis. Phillips utilized water sampling of canals pre- and post-demucking and traditional survey exercises to evaluate more accurate options for the as-built survey than the bathymetric survey. Phillips coordinated with FPL on proposed as-built alternates to the bathymetric survey and agreed to a more accurate traditional survey for as-built verification.