Cleaning up the Keys
Vacuum sewers reduce wastewater problems that threaten the
islands’ aquatic environment and economy.
Ernest Hemingway, the most famous former
resident of the Florida Keys, knew he was living in paradise
when he wrote, "It’s the best place I’ve ever been anytime,
anywhere – flowers, tamarind trees, guava trees, coconut palms...”
Hemingway was ahead of his time. Today, more than three
million visitors come to the Keys each year to enjoy the beauty and lifestyle
that Hemingway found so appealing. Tourism is the number one industry on
the archipelago. Visitors come for sun, scuba, sailing and scenery. Many
who come to visit end up living here year round.
The influx of people and burgeoning economy has come at a price for the Keys. In the 1980s it was discovered that pollution, largely from wastewater, had reached dangerous levels. The magnificent coral reefs and marine life, which are the foundation of the region’s tourism industry, were in jeopardy. Tropical and game fish were endangered and some bodies of water became unsafe for swimming. Residents, as well as local and state officials, began to realize that a great natural resource was dying unless they addressed their need for proper wastewater management. In 2000, the Florida State Legislature mandated that the Keys have a suitable sewer system and treatment facilities, including nitrogen and phosphorous removal, in place by mid-year 2010.
“The reefs here are incredible,” said Chuck Fishburn, general manager
of the Key Largo Wastewater Treatment District. “Virtually everyone
who is here came here because of the water; the fishing, diving and boating. We
understood that if we didn’t get central sewers, we would eventually kill
off the reason we’re here.”
GETTING BUSY
The Florida Keys encompass a large geographic
area, approximately 137 square miles covering 17,000 islands, of which
35 are considered “major” islands. More than 80,000 people live year-round
in the Keys and an estimated four million tourists visit the islands
each year. Providing sewer service to such a large area and involving
several entities presented a sizable challenge for project planners.
Civic and public works officials began the task
by getting organized in their own areas. They prioritized the work,
reviewed various proposals and sought funding. After conducting a significant
amount of research, initial projects were constructed at the Ocean
Reef Club in the Upper Keys, the Little Venice area of Marathon in
the Middle Keys, and Stock Island in the Lower Keys. In each case they
installed vacuum sewer collection systems.
“The circumstances we face here in the Keys led us to select vacuum sewer technology,” said Chuck Fishburn. “We went through the installation process and then saw how the system worked and we were very pleased with the outcome. Based on those initial projects, we decided to utilize vacuum sewers wherever we could.”
Having made the decision to install vacuum sewers, both the
Key Largo Wastewater Treatment District (KLWTD) and the City of Marathon began
advertising for engineers who had experience with the technology. Eckler Engineering
of Coral Springs, Florida, and Weiler Engineering of Marathon had both designed
vacuum systems throughout South Florida and were an obvious fit. They were
two of several engineering firms that were involved with this enormous effort.
GlobeTec Construction of Deerfield, Florida, was one of several regional construction
companies selected to do the installation.
“We were part of the team that installed the first vacuum system in the Florida Keys in 2001 and 2002,” said Jorge Fonte, vice president of GlobeTec. “We probably have installed more than 1,300 valve pits and 200,000 linear feet of vacuum lines.”
AIRVAC, a leader in vacuum sewer technology headquartered
in Rochester, Indiana, was selected to provide the components and design
support for the project.
“AIRVAC developed most of the specifications used in
vacuum system design so it’s always good to have their expertise for
a job as big as this one. They have worked well with us to create a fail-safe
functioning system that will experience minimal problems in the future,”
said Don Eckler, P.E., president of Eckler Engineering
THE MASTER PLAN
There is an enormous amount of sewer construction work going on throughout
the Keys right now, and it all started more than 10 years ago with
a master plan.
In 1999, Monroe County, which comprises 95 percent of the Keys, wrote
a voluminous document called the Year 2010 Comprehensive Plan. The
study cited the scope of the problem: 246 small wastewater treatment
plants operating on the islands along with approximately 7,200 cesspool
and cesspit systems, many of them illegal. Combined, they contributed
more than seven million gallons a day of wastewater, most of it containing
pollutants that are detrimental to aquatic life living in the ocean.
At the heart of the problem were the thousands of cesspools across the
islands. Cesspools in the Keys provided poor wastewater treatment
because most of the islands sit atop a layer of coral rock, which is
very hard yet porous. The rocky soil did little to remove the pollutants
in the wastewater, allowing it to seep into the groundwater and eventually
into the canals and ocean surrounding the islands. Studies showed
traces of fecal coliform bacteria on the reefs in amounts that would
damage the reef itself and the surrounding marine life.
“Twenty years ago the canals were clean enough to swim in. They
had tropical fish in them,” explained Fishburn. “Today, the water
is so murky you can’t see through it anymore.”
The geography of the Keys presents several significant challenges that
could have made a sewer construction project extremely difficult and
prohibitively expensive.
“In the Keys you have flat terrain, high groundwater, developed neighborhoods
and difficult soil conditions; all of these create problems when designing
and installing sewers,” said Eckler. “Then there is the added difficulty
of maintaining traffic on U.S. Highway 1 while installing a sewer system. Highway
1 is only road in and out of the Keys, so it is always busy and must
remain open. Plus, the side streets are narrow which presents the
challenge of keeping them open for emergency vehicles during the construction
process.”
Gravity sewers, low-pressure systems and vacuum technology all were
considered, but a life-cycle cost analysis revealed that vacuum sewers
would be the best option. The prospect of digging through coral
rock with high groundwater was considered an enormous obstacle. A
gravity system would have required trenches as deep as 10-15 feet to
achieve the grade necessary to move sewage from homes to the treatment
plant. Cutting through rock and constant dewatering, while trying
to maintain traffic flow, would make the project incredibly expensive,
time consuming and disruptive for Keys residents.
Engineers also considered the number of lift stations that would have
been required to transport wastewater in such flat topography. Key
Largo alone would have needed 50 or more lift stations. In a place
like the Keys where land is so valuable, the property costs alone would
have made the project extremely expensive.
Low-pressure sewers offered many of the same advantages as vacuum sewers
in terms of pipe size, trench depth and limited traffic disruption, but
the life cycle costs were higher than those of vacuum sewers. This
was mainly due to the sheer number of grinder pumps that would be required
for the Keys project and the associated maintenance costs. Each
dwelling would require a grinder pump and electrical connection to the
dwelling. For many of the small homes in the Keys, this would have
required an upgrade to their electrical system. Furthermore, power
outages, which are common in this region, would have shut down the system
unless each grinder pump had its own generator, which is not practical.
“The analysis done by the engineers back in 2000 clearly showed the
advantages of installing vacuum sewers,” said Fishburn. “Simply
stated, vacuum lines require only half the slope of gravity mains and
can transport wastewater uphill by means of a saw-tooth profile. That
means shallower trenches and less digging. There also was the fact
that one vacuum station could do the job of several pumping stations,
and there were fewer electrical requirements. In this situation,
the decision to install vacuum sewers was an easy one.”
VACUUM POWER
Vacuum sewer technology solved many of the problems that are inherent
in the Keys. The shallower trenches needed for vacuum lines helped
avoid many of the cost and labor issues that deep trenching would have
required. The trenches for the vacuum lines were typically 4-6
feet deep. Little dewatering was needed, there was less disruption
to the established neighborhoods and because the vacuum mains were
made of smaller diameter PVC pipe, the installers could use less and
smaller equipment.
“The footprint required for construction is significantly smaller,”
said Fonte. “Fuel consumption also is much less (than a comparable
gravity sewer installation). I would estimate we used about 30
percent less fuel than we would have on a gravity sewer job. The technology
is also faster to install than gravity or low-pressure systems. Crews
installed anywhere from 300-800 linear feet of collection lines per day.”
The design engineers and installation crews also received the benefit
of AIRVAC’s years of vacuum sewer experience. As Fonte noted, underground
infrastructure projects can be unpredictable, so experience and flexibility
are critical during installation.
“There are always a lot of unknowns in an underground construction project. It
was extremely helpful to have AIRVAC there to make suggestions and provide
advice when we encountered unexpected problems. They have always
been great to help come up with workable solutions.”
BONUS BENEFITS
Ease of installation was a significant factor in choosing vacuum technology
for the Keys’ sewer system, but there were numerous other benefits
that made vacuum sewers a perfect fit for this situation.
Public works directors who live and work along the southeast coast of
the United States are aware of the threat of hurricanes. Hurricanes
can damage or destroy pumping stations, dump tons of sand into the treatment
system and, perhaps worst of all, disrupt electrical power and thus knock
out a city’s sanitary sewer collection system.
Vacuum sewers are less vulnerable to electrical power loss for several
reasons. In an AIRVAC system, the sewage from houses and businesses
flows by gravity to the AIRVAC valve pit, which is usually buried near
the street. When the wastewater in the pit reaches a predetermined
level, the valve opens pneumatically to release the sewage into the collection
line. No electricity is needed to operate the valve pit.
Each of the six vacuum stations on Key Largo is equipped with a backup
generator, so there will be no loss of sanitary sewer service even if
the power is out. A gravity system would have required five or
six times as many pumping stations to serve the 14,000 residents and
tens of thousands of tourists, and each station would need electricity
and daily attention to remain functional during a disaster.
Also, because vacuum sewers are a closed system, there is no infiltration
or exfiltration, any breech of the collection line is detected almost
immediately. Salt water and ground water are kept out of the treatment
plant, and that reduces treatment costs and equipment degradation.
 In designing the system, engineers came up with some extremely innovative
ideas that paid some immediate benefits and will help utility workers
for years to come. Because vacuum collection lines are water tight,
they can be laid in the same trench with stormwater collection lines
and reuse water lines, saving installation time and valuable space. Furthermore,
during the daily inspection of the line installation, the inspectors
mark coordinates with a GPS device. This will help public works
personnel create a detailed map of buried infrastructure. Such
a map will be invaluable in years to come.
“It’s great to know exactly where your utilities are buried, especially
in a natural disaster like a hurricane. If a street is wiped out
or buried in sand, we will know precisely where the collection lines
and valve pits are buried,” explained Dan Saus, wastewater project manager
for Weiler Engineering in Marathon, Florida. “They also snapped
photographs when they took the coordinates. So when you go into
their system and click on a data point, you’ll actually see a photo of
what is buried there. It’s like having x-ray vision.”
AWARD WINNER
Environmental awareness has always been a priority among conscientious
public works professionals. That is certainly true in Marathon
where their sewer design has won praise as an example of “green” infrastructure.
In 2009, the City of Marathon received the Pisces Award from the Environmental
Protection Agency for projects that represent a commitment to the state’s
aim to achieve sustainable water quality. Marathon was the only
city in Florida to receive the award.
“I don’t think I’ve ever seen a team of public works professionals who
were as progressive as this team was,” commented Susie Thomas, director
of community services for the City of Marathon. “It’s really a
tremendous honor and we’re very proud.”
Marathon’s design won the award in part because of the innovative one-trench
design for installation, which includes both sewer and stormwater piping,
and was made possible because they installed a closed vacuum system along
with the GPS mapping work. They also were lauded for designing
a system that produces reuse water, which will provide one million gallons
a day of water that can be used on golf courses, football fields and
public parks.
Of course, the most important objective of the massive Keys project is a cleaner
aquatic environment in and around the islands. When all of the communities
throughout the Keys complete their sewer collection and treatment systems, then
we will begin to see cleaner water throughout the area. The tourism industry
will remain vibrant and the residents of the Florida Keys can again enjoy one
of the most beautiful natural environments in the world.
This article appeared in the September, 2009 issue of CENews. 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 the Florida Keys can be found in our Large Municipal Project Gallery.
Return to Large Projects page.
|
