- February 28, 2023
The town of Longboat Key has identified a more cost-effective solution to its parallel sewer main project, and work has begin on initial stages on the mainland side of the pipeline.
Originally, a brand new pipe was planned to run parallel to the existing pipe, which went into service in the 1970s. The original pipe was built with the expectation of a population one day exceeding 50,000 residents. But a 1984 decision to rezone the island changed the trajectory of island growth, limiting peak season population to about half that number.
Taking advantage of that sewer-capacity margin, town staff identified a more cost-effective solution called slip-lining. A new, smaller, more durable pipe will be fed within the existing pipe. The new pipe is expected to last between 75 to 100 years.
“It is considered to be much more durable and long lasting than ductile iron,” Public Works Director Isaac Brownman said. “It is much less reactive to corrosion. It’s not like an iron metal material that reacts to what is underground; it is a very static material.”
Improvements follow a pipeline break in June 2020 that spilled millions of gallons of effluent in Manatee County.
The initial project’s overall cost is estimated to be about $2.6 million. The majority of the costs, $2 million, is covered by state appropriations received over the last two years as part of the broader effort to improve the sewer main.
The existing pipe measures about 20 inches in diameter, whereas the new one is 18 inches.
The entirety of the pipeline from the town to the county’s treatment facility measures about 4 miles. About 1.2 miles will be relined with the upgraded material.
Currently, the town is only working on construction for the mainland portion, which will start at the leak repair point, approximately 400 feet north of Sarasota Bay to the Manatee County meter located at the county’s Southwest Water Reclamation Facility.
The town’s contract is with Murphy Pipeline Contractors. The company completed the design and will place the new pipe.
The town owns about three-and-a-half miles of the pipeline from Longboat Key all the way to the meter on the mainland. The remaining portion belongs to Manatee County. The town is responsible for all construction and design, but Brownman said the county has been “extraordinarily cooperative” in the coordination of the project.
In order to accomplish the work as seamlessly as possible, the contractor will set up a bypass system to maintain island flow and operation during the work. Longboat residents should experience no disruption to service, Brownman said.
“(The contractors) have to connect to our existing pipeline just before slip-lining it and run an equivalent pipe above ground all the way to the Manatee County meter,” he said. “Our system will be online the entire time, but running through a bypass system all the way to the meter. The contractor will then slip line the pipes before we put the existing line back into service.”
The current tentative construction schedule is as follows:
The total cost for replacing the entire sewer line was originally estimated to be about $24.8 million when the town was going to build the parallel pipe, but with the new method for the mainland portion the new estimated cost is about $21.7 million or lower.
A few approaches have been considered to build a redundant pipe across the bay, including the most aggressive approach, open cutting. Open cutting is a method of pipeline installation that requires digging up the underwater bed of Sarasota Bay to the required depth for installing the pipe.
“We have to get a barge out there with an excavator to scrape that out, put the pipe under the bay, all that is pretty involved,” Brownman said.
The town this year also launched an incremental increase in water and sewer rates in anticipation of borrowing not only for the pipeline project but also to replace water pipes in Country Club Shores.
Beginning in 2022, the town's water and sewer rates were reset to begin climbing to help pay for the sewer line and the Country Club Shores work. From an average bill of $74.75 in 2021, bills will climb to $105.30 by 2029. With the additional revenue, the town can afford to borrow the remainder of what it needs for the two water and sewer endeavors.