HDD Helps Repair Decades-Old Water Main Leak in Fragile Coastal Environment
Prepared for the 2013 NASTT No-Dig Show by Blake Peters, PE, McKim & Creed, and Seton Katz, PE, Sarasota County Capital Management Services
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Abstract
In the 1990s the water main that connects Siesta Key, Florida to Casey Key began failing in a sensitive wetland between these two barrier islands. The 8-inch cast iron water main was built in the 1970s and was situated almost entirely within an environmentally sensitive bay and marine preserve, making the main inaccessible for repair. To minimize water loss, Sarasota County partially closed valves at both ends of the crossing, but that reduced available pressure and was not a long-term solution. Replacing the main was very important to restore water quality, water pressure and fire-flow reliability on both keys, which were lengthy dead-ends without this ‘interconnecting’ pipeline between them.
The County considered several repair alternatives, but most had unacceptable environmental ramifications, high construction costs and/or were not acceptable to the adjoining public. In 2012, after years of pursuit, the County obtained the last of the needed land rights and permits to proceed with a horizontal directional drill (HDD) solution that replaced the leaking watermain and minimized impacts on native habitats and species, reduced environmental mitigation requirements, and lessened the effects of construction to the public.
The sub-aqueous crossing was successfully completed using 2,765 feet of 10-inch diameter HDPE pipe installed by HDD. Extensive planning and careful execution were needed to overcome the project’s many risks, which included limited access, limited staging, potential for hydro-fracture, species impacts or property damage. Other challenges included avoiding an existing seawall, limiting impacts to the public and obtaining easements from the adjacent property owners.