Tiny Alloway Township
Saves Big with
Vacuum Sewers
No one will ever mistake Alloway, New Jersey, for New York
or Philadelphia. Alloway is a tiny town (population 2,500) located in the Southwest
part of the state just a few miles from the Delaware River. Yet, Alloway has
something that even major cities can only dream of – a state-of-the-art sewer
system that’s low maintenance and environmentally sound.
Alloway’s new wastewater collection system, which was completed in September, 2009, is perhaps the most advanced sewer in the Mid-Atlantic region. It utilizes vacuum sewer technology to convey the community’s sewage to nearby Salem, New Jersey, where the effluent is treated and discharged. The system replaces hundreds of septic tanks that were creating an environmental problem for local residents and New Jersey’s Department of Environmental Protection.
Alloway had been looking to replace its septic tanks for decades. A new sewer was first proposed back in the early 1970s, but cost and inconvenience delayed the project until 2007. When engineers first looked at designing a conventional gravity sewer, they realized that Alloway presented numerous and significant installation obstacles.
Sewer collection lines must be laid at an incline to
achieve the grade require for gravity flow. They also needed three pumping
stations to keep the flow moving to the treatment facility. The engineers
estimated that to achieve the necessary grade in the line, the pipes
would need to be buried 22-24 feet deep. Because the area around Alloway
has a high groundwater table, this would mean extensive excavation and
dewatering, both of which add significantly to the cost of any project.
Furthermore, the excavation would destroy most of the local roads and
disrupt traffic and neighborhoods for many months. These were just a
few of the challenges that would be created by installing a gravity sewer.
In need of cost-effective options, the engineers examined
the possibility of installing vacuum sewers. AIRVAC, Inc., a leader in
vacuum sewer technology, was asked to make a proposal. Their approach
to the problem changed the course of the project and gave Alloway an
intelligent alternative to its sewer collection problem.
 VACUUM SEWERS 101
Homeowners typically don’t notice the difference between
a vacuum sewer and any other collection system. Gravity lines transport
sewage from the home just like they do in a gravity system, but at the
street or property line, the sewage empties into a buried valve pit.
Inside the valve pit is a patented AIRVAC pneumatic valve. It requires
no electricity, so there are no electrical lines to worry about and the
valve will function even during a power outage. When 10 gallons of wastewater
accumulate in the pit, the valve opens automatically and differential
air pressure propels the contents into the vacuum main.
Because vacuum lines do not rely on gravity to transport
sewage, there is no need for deep-trench excavation. Vacuum lines are
typically buried 4-6 feet deep, so no dewatering was necessary. Shallow
trenching means less heavy equipment and less disruption of neighborhoods
and traffic. The design also called for only one vacuum station, rather
than three pumping stations for a gravity system. This was another significant
cost savings.
The sewage within the collection line travels at speeds
up to 18 feet per second, scouring the line along the way. Negative pressure
in the pipeline is created by vacuum pumps located at the vacuum station.
The vacuum station looks much like the surrounding architecture. It covers
a relatively small footprint and can be placed almost anywhere, even
in a residential neighborhood.
Vacuum sewers are contained systems, so the municipality
doesn’t have to pay to treat infiltration or storm water. At a cost of
approximately $6 for every 1,000 gallons of treated water, the savings
in treatment cost is significant. Vacuum sewers do not leak, there is
little to no odor and workmen almost never come in contact with raw sewage.
In fact, there are no confined entry requirements for workmen. Very little
maintenance is needed and the system requires less electricity than a
comparable gravity system since we only have one vacuum station rather
than three pumping stations.
Sewage arriving at the vacuum station empties into a
collection tank. When liquid in the tank reaches a specified level, sewage
pumps activate and transfer the contents into the force main and on to
the treatment plant.
SAVING MONEY AND THE ENVIRONMENT
Installing AIRVAC sewers rather than gravity sewers
saved Alloway taxpayers approximately $1 million, or about $180 annually
for each user over 40 years. Saving money was an extremely important
consideration, but there were other significant benefits, as well.
Perhaps no other sewer conveyance system is more environmentally
sound than vacuum sewers. With vacuum sewers you eliminate the problem
of exfiltration of raw sewage into the environment. Any time a leak develops
in an AIRVAC sewer line, the vacuum pressure within the line prevents
sewage from escaping into the environment, thus protecting the groundwater.
You also know about leaks immediately because the system is monitored
electronically at all times. When a leak or damage occurs, the trouble
spot is easy to find and isolate, and because the lines are buried in
shallow trenches, excavation and repair is easy and fast. Repairing a
vacuum line takes only a few hours, compared to days or even weeks to
fix a deep-trench gravity pipe, and often gravity sewer leaks go undetected.
When we first proposed vacuum sewers in Alloway, we had to obtain approval
of the design from the New Jersey Department of Environmental Protection.
Virtually every person involved with wastewater collection and treatment
in the department attended the meeting to hear about vacuum sewers. After
the presentation, the general consensus was that vacuum sewers are the system
of the future.
The Village of Alloway will also benefit from operational costs
for years to come. The system itself requires very little maintenance
and very little energy is required to operate it.
 Because
it was the first system of its kind in this area, there were no contractors
nearby with vacuum sewer experience. This turned out to be a non-factor,
as installation proved to be relatively easy. If you encounter an unexpected
underground obstacle, you can divert the line around, over or under it
without significant cost or delays. AIRVAC provided a field service representative
who was available at all times to answer questions and offer advice.
As a result, the installation process was virtually trouble free.
We’re confident that the vacuum system we now have will serve Alloway’s
residents for many years to come. The track record for the durability
of vacuum technology is good; the oldest vacuum systems in the United
States are now more than 30 years old and still going strong.
The news of our sewer success is beginning to spread to sister cities
in New Jersey. We’ve conducted several tours in recent weeks for engineers
and municipal employees who want to know more about how vacuum technology
works. We are always happy to oblige their requests.
This article appeared in the November, 2009 issue
of New Jersey Municipalities Magazine. If
you would like to read the entire story as it appeared in the magazine,
you can download
a pdf, or you may request
hard copies. Additional information and photos of
the installation of vacuum sewers in Alloway, New Jersey can be found
in our
Municipal Project Gallery.
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