Coastal Communities Turning To Vacuum Sewers

By Tom Nicholson

Teaming designers and builders in integrated project delivery has streamlined work on numerous building and road construction projects, saving time and money and freeing owners from change orders and multiple contracts. Now, design-build project delivery also is showing up on underground pipe-laying projects where contractors work side-by-side with designers in developing optimal plans before digging in.

That’s how things worked out over the past two years on a sewer project in Ponte Vedra, Fla., where Jacksonville-based Callaway Contracting Inc. teamed up with Coral Springs-based Eckler Engineering Inc. for a $10-million design-build job commissioned by the Jacksonville Electric Authority. The project involved construction of an innovative Airvac vacuum sewer system in the 672-home Ponte Vedra Beach subdivision, which previously had individual septic tanks for each home. The work included burying 45,000 ft of 6 in., 8 in. and 10 in. PVC pipe, installing one valve pit for every two homes and constructing a pump station with three 25-hp vacuum pumps capable of moving 450 cfm of wastewater.

JEA merged with the Jacksonville Public Works Dept. in 1997 and now operates JEA Sewer System, which includes six regional wastewater treatment plants and 2,500 miles of collection lines. The state ordered JEA and St. Johns County to install a sewer system at Ponte Vedra after the state Dept. of Environmental Protection conducted tests in nearby lagoons and found contamination from the subdivision’s hundreds of septic tanks.

The high water table in the ocean-side community compounded the pollution and also would have complicated construction of a gravity sewer system, which would have required deep trenches. "JEA’s typical method of sewer collection has been traditional gravity," says JEA spokesman Greg Corcoran. "After quite a bit of research, JEA became convinced that vacuum sewer collection could provide an acceptable alternative and, given the right conditions within a project area, the use of vacuum could potentially be installed at a cost savings over traditional gravity. Ponte Vedra provided these favorable conditions so vacuum sewer became the system of choice." Click here to view rendering

With cost savings in mind, JEA and county officials opted to do the project under a design-build contract. "JEA felt the design-build method of delivery was best suited for this particular project [because] the vacuum sewer technology was a new system for JEA and we felt the use of a design-build firm would provide the expertise needed to design and build [it]," Corcoran says. "The goal was to create a concept of ‘total responsibility’ for the design-build team." JEA is a knowledgeable owner, having previously used design-build on upgrades to wastewater treatment plants and new chilled water plants and felt comfortable applying it to a sewer grid.

Leading Edge

	Vacuum system uses smaller diameter, lightweight pipes and shallow trenches. (Photo by Ed Stephenson)

JEA published a request for qualifications for the job in mid-2003, and after reviewing a pool of eight respondents, short-listed three firms. Calloway got the nod, despite its lack of experience with design-build or vacuum sewer projects. It was a selection based largely on their past working relationship with JEA. "We had done about $50 million of work with JEA before, doing water lines and pipe laying projects," says Callaway’s project manager Stan Bates. "We had never done design-build before and it was also the first time for JEA on a sewer project, so this was a learning process for both of us."

Corcoran says respondents were evaluated for qualifications in safety, project-related knowledge, record of past performance, resources and financial responsibility. "Although many exceptional teams responded to the RFQ, JEA’s evaluation team felt Callaway Contracting’s abilities gave them the edge over their competitors," he says.

With Callaway in the driver’s seat, the next step was for it to choose a design firm as well as determine which vacuum system would be best suited for the job. "We talked to two vacuum sewer companies about their product and also asked if they could recommend an engineer for the job," says Bates. "In the end we felt Airvac was the superior product."

Rochester, Ind.-based Airvac’s prominence in the vacuum sewer field, and its comprehensive support plan were big factors in the company’s favor. Airvac provides clients with an onsite field representative during construction who stays on location for the job’s duration to assist contractors with the installation. The company also offers a week-long training program as part of its contract in which owners can send two representatives to the company’s Rochester training facility. When possible, Airvac also will arrange long-term operational support from a qualified technician if one is located nearby.

Premanufactured collection tank module is dropped into concrete block vacuum station. (Photo by Ed Stephenson)

For the design duties, Airvac representatives recommended Eckler, which had done several other Airvac jobs in Florida, including a project in Palm Springs in 2001 involving 15,000 ft of pipe. Eckler’s experience with vacuum system technology was highlighted by its work with the U.S. Environmental Protection Agency, which has asked the firm to assist in writing federal standards for the burgeoning technology.

"When we talked with Eckler it felt right, it felt like it would be a good team," Bates says. Eckler was onboard not only to draw up design plans, but to lend Calloway its vacuum sewer experience and guide the team through the installation process.

The team broke ground in December 2003 and finished by May 2005. The time frame of just under two years is much faster than a comparable gravity sewer system. Time was saved by using integrated project delivery and the much shallower pipe depths made possible with the vacuum sewer system. "The deepest lines were about 8 ft and the average depth was between 4 ft and 6 ft," says Bates. "With gravity systems, you are at depths of 20 ft to 21 ft, which is very disruptive and time consuming. That made this job very easy, relatively speaking."

Design-build delivery helped the team trim time by tapping the contractor’s opinion during the design phase, enabling Eckler to establish the best, most efficient, design plan. What resulted was a design that called for the pipe to be buried beneath the roadway, as opposed to alongside of it, which at first seemed the likely place to lay the pipe, says Eckler President Don Eckler. Before drawing up a design, "we asked, ‘What’s best for the contractor in this?’" says Eckler. In response, Callaway pointed out that the swale was so full of utilities, including all the subdivision’s electric and gas lines, that "it would have made it extremely difficult to dig and lay the pipe there," Eckler says.

The plan to lay pipe under the roadway was was made even easier by the fact that St. Johns County already had removed much of the road surface in the subdivision in preparation for a resurfacing project. "We saved a tremendous amount of time doing it that way," Eckler says. "We were able to see the design from the contractor’s standpoint and we came up with the best design because of that. That was a result of working in a design-build environment."

Although it was a design-build job, the contract required Eckler to submit completed designs before construction began. "It wasn’t a typical design-build job in that aspect," says Eckler. "But since we were teamed with the contractor we were able to work with them throughout the design process." That provides "a whole different mentality" than traditional project delivery, says Bates. "It’s worked out well with Eckler. They would advise us on the way things should be done and then we would apply it in the field," he says.

	Airvac field services technician (in red hardhat) helps supervise valve pit installation. (Photo by Ed Stephenson)

Eckler’s vacuum system experience came into play when the engineer suggested that the vacuum be tested on a daily basis at the end of the workday, a frequency that is above and beyond what’s required. "That was not part of the contract but they asked us to do that and that was based on their experience," says Bates. He explains that as pipe is laid, the vacuum pressure must periodically be tested to determine how much energy is lost due to distance from the pump, or from diverting up and around other utility lines. "We followed their advice and tested daily," Bates says. "It was a good idea that helped us foresee any conflicts down the road. If there was loss of vacuum we would know where it was before we got too far along."

Sweet Success

Vacuum sewer technology emerged about 30 years ago as an alternative to gravity systems where geography or limited work zone space made deep digging impossible. With technology advances, vacuum sewer systems are gaining viability among designers and contractors, not only as a last resort in special circumstances, but as an option based on its own merit and strengths.

The typical system works like this: A pump station containing three 25-hp pumps is installed centrally to the scope of the system. From each home, a gravity service line of small-diameter PVC pipe connects to a sump valve in a fiberglass valve pit, typically buried just outside the homeowner’s property line. The Ponte Vedra job used 359 such valves.

The pneumatically operated valve opens when 10 gallons of wastewater accumulates in the sump. Air from an intake pipe that emerges above ground at each home then breaks the seal in the pit and allows the water to be pulled by the vacuum through the sewer lines toward the pump station.

The sewer lines are installed with a slight slope toward the vacuum station. The lines are placed in vertically zigzagging "saw tooth" patterns that take advantage of gravity flow and vacuum assist. Lines use 45° elbows to go around obstacles such as utility lines. Sewage is sucked through the mains at a rate of 15 to 18 fps to the pump station and is collected in a tank until it is forced out into a gravity main that carries it on its way to a treatment plant.

On level terrain, a vacuum station can serve up to 1,200 homes through mains up to 10,000-ft long. There typically are three pumps housed within the station, but the operation relies mainly on two, with the third serving as a backup that kicks on during peak hours. The pumps run on electric power.

Airvac has installed a total of 250 vacuum sewer systems in 27 states. Company spokesman Rich Naret says its use is contingent on geography, noting that the system needs level ground for operation and is not viable for hilly terrain. "It’s being used mostly in coastal areas," says Naret. "It works well in a place like Ponte Vedra where it is flat. It is good for jobs where there is a high water table like along the coast in Florida or other coastal states. One of the hottest places right now for us is North Carolina."

Vacuum sewers are attractive to owners because "there are no manholes and no odors," says Naret. "And since excavation is not as wide or deep as on a traditional system there are no trench walls, which is a safety issue. Trench cave-ins are never a good thing. Installation is generally less intrusive than with a gravity system."

Time saved through shallower excavation cuts construction costs, but Naret says that owners considering vacuum sewers must weigh reduced installation costs against the costs of installing necessary components, such as the vacuum valve pits and a pump station. "There’s really a trade off," Naret says. "It’s less expensive but there is also a big pump station that has to be built."

Naret says vacuum sewer projects are beginning to be performed more frequently as design-build jobs after a slow start in general for sewer work. "Utility sewer work has mostly gone the traditional route," Naret says. "Design-build is popular for things where you can see a structure. It’s a bit different with underground work because you can’t see it and it has taken a while for underground work to catch up with design-build."

Other design-build vacuum sewer projects include a 259-valve Airvac installation that was completed in 2003 in Provincetown, Mass., by the team of North Harwich-based contractor Robert B. Our Inc. and Wakefield-based engineer Metcalf & Eddy Inc. One massive project currently out to bid is an estimated $180-million job in the Florida Keys town of Marathon that is scheduled to be completed in 2010. That project will involve 1,600 valves and seven vacuum pump stations and will service 10,000 homes.

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