CAROLINA COASTAL COMMUNITY FACES Sensitive Sewer Line Rehab.
Add to this a community with a great regard for its history and its preservation, and you have a witches' brew of potential problems that many utility contractors never encounter in a lifetime. All of these challenges were involved with the rehabilitation of 4,000 ft of sewer line in Beaufort County. Beaufort is located in South Carolina's low country on the Atlantic Ocean, just north of Hilton Head Island. Its 691 sq mi includes 64 major islands and hundreds of smaller ones. The county is about 21 ft above sea level, and the soil is mostly sandy.
The site of the pipeline restoration project was on Lady's Island, a minimally developed island that still maintains a great deal of its pristine quality. The island's development started in the 1970s, but apparently one developer installed part of the utility infrastructure and then gave up the ship. A short time later a second developer completed the infrastructure and started development without regard for the locations of sewer and water lines. Sewer lines run "under" residences, a golf course, a marina, and other amenities.
The island and its Marsh Harbor development became the responsibility of the Beaufort-Jasper Water & Sewer Authority in 1997. Director of Operations Dyke Spencer says the lines were video inspected before the responsibility for the line was transferred to BJWSA. "We knew what we had," he says. "It didn't take a lot of investigation. During heavy rains it was obvious that infiltration was exceedingly heavy. We knew what had to be done; we just needed the money and the right technology."
The money came from impact fees charged developers when they connect new housing projects to the system. The technology, called U-Liner[R], came from the Pipeline Rehabilitation Division of CSR Hydro Conduit (Houston, Texas). "We examined our options and settled on U-Liner," says Spencer. "The price was right and the U-Liner met the performance specifications required."
The deteriorating line was eight in. in diameter. It consisted of 1,500 ft of concrete, 843 ft of PVC, and 1,700 ft of concrete truss pipe.
There were no abstracts delineating the line location. Wastewater Manager Chris Petry tracked the line from manhole to manhole. There were 15 in all, and three proved difficult to locate. In addition, the existing line contained dozens of hammer taps. With hammer taps, lateral lines are simply driven through the wall of the main line, leaving unsealed penetrations that protrude into the mainline. Each hammer tap protrusion had to be cut off flush with the wall of the main line and the penetration sealed during the rehabilitation process.
The liner was manufactured to length, and the high-density polyethylene pipe was inserted from manhole to manhole. No excavation was required. The liner is deformed in the manufacturing process into a "U" shape about one-half the diameter of the host pipe. At the installation site, the liner is pulled through the damaged pipe and then reformed by a heat/pressure method to securely fit the shape of the host pipe. The end result is a structurally sound "pipe within a pipe."
The job, says Petry, took 45 days, and no serious problems were encountered. The only significant inconvenience was to Paul Jernigan at Marsh Harbor Marina & Boat Yard. "The line ran through a section of his yard," says Petry, "and we needed him to move boats back and forth, but he was very cooperative as were all the residents of Marsh Harbor."
Before the project started Spencer and Petry made sure all residents were informed of what was to be done, how long it was to take, and what vehicles and equipment would be used and in view for a few weeks. "Everyone took the project in stride," says Spencer. "They knew what we were doing and why, and they were glad to have this problem solved."
Spencer said no inflow/infiltration studies have been done since the rehab was completed, but flow meter readings at the pump station show a 20 percent reduction.
The technology used on this job made excavation unnecessary in a sensitive environment. In addition, the repair of the line made it feasible to connect the system to a regional sewer system. The regional system connection eliminated the need for a waste treatment package plant on Lady's Island that had been discharging into the nearby Beaufort River.
Because of its rapid growth, the development and maintenance of an effective utility infrastructure is among Beaufort County's most vital needs. If significant excavation had been necessary on the Marsh Harbor project, the community might have become much less tolerant of the current rate of growth.
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|Date:||Nov 1, 1999|
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