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This editorial was published in CE News February 2005 issue.

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To view photos of the AIRVAC vacuum sewer installatios in Englewood, Florida
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Storm Survival

Vacuum sewers withstand Florida's hurricane barrage.

 

Catastrophic weather is a public works director’s worse nightmare.  A massive storm can wreck infrastructure on an epic scale, and the costs to the city and the local economy can be staggering. Public works directors in Florida will forever remember 2004 as the “Year of the Hurricane.”  Four major storms, all Category 2 storms or worse, pummeled the peninsula during a six-week period.  The last time four hurricanes hit one state in a single year was in Texas in 1886.


For officials responsible for sanitary sewer operations, hurricanes are especially troubling.  The loss of electrical power, a common occurrence with hurricanes, means that pump stations shut down.  Raw sewage can back up into homes or spill out into the environment.  Public works personnel have to scramble to get portable generators on line to keep sewage flowing.  Meanwhile, massive amounts of stormwater infiltrate the system and overwhelm treatment plants, which then have to bypass untreated combined sewer overflow into local streams and rivers.


Public works directors all over Florida had to deal with these and other sewer-related problems during the aftermath of hurricanes Charley, Frances, Ivan and Jeanne.  However, a few communities using vacuum sewer technology survived the hurricanes with few, if any, sewer issues.


Hurricane damage in FloridaHurricane Charley made landfall on Friday, August 13, along the Southwest Florida coast. Packing nearly 150-mile per hour winds, it was the most powerful storm to come ashore since Hurricane Andrew in 1992. Stock Island, located just a few miles northeast of Key West, took a glancing blow from Hurricane Charley, knocking out electrical power for several hours.


In 2003 the community had installed an AIRVAC vacuum sewer system to serve several hundred of its residents.  The vacuum station is housed in a building that is above the 100-year flood level and strong enough to withstand a Category 5 hurricane.  The island also has force main gravity sewer system with 16 lift stations.  Both systems are serviced by Keys Environmental, Inc. based in Key West Fla., under contract to Key West Resort Utilities.


When power is lost at lift stations, crews often have to bring in large portable generators to maintain sewer service.  Christopher Johnson, president of Keys Environmental, Inc., noted that handling large three-phase generators in high winds and pounding rain is not only difficult, it can be dangerous. Fortunately, the vacuum sewer system required minimal attention both before and after the hurricane hit. A standby generator kicked in when electrical power was lost, and it maintained service until power was restored. Johnson also noted that several mainland communities with gravity systems were still without sewer service weeks after the hurricane had come and gone.


With a vacuum system, one vacuum pump station often can replace seven or eight lift stations, a significant benefit for public works departments that must decide whether to invest in expensive backup generators for each station and that have to prepare each station for oncoming storms.


“When we assess our Hurricane Preparedness Plan, the advantages of the vacuum system really stand out,” said Johnson.  “The preparation that is required to ready the vacuum system is miniscule compared to the enormous amount of effort it takes to prepare the force main/gravity system.”

 

For example, in Englewood, Fla., about 30 miles northwest of Fort Myers, Fla.,  about two-thirds of the community’s sewer system is vacuum and about one-third is conventional gravity sewer.  There are five vacuum pump stations, but 60 lift stations for the gravity sewers. “We have a lot of work to do in preparation for a hurricane,” said Mike Ray, operations manager for Englewood Water District. “We had all kinds of problems with our gravity sewers but the vacuum sewers never missed a beat,” Ray continued.  “If all our sewers were gravity sewers we would have 150-200 lift stations.  You can imagine the amount of work it would require to keep up with that many lift stations before and after a hurricane.  We don’t have the budget or the manpower to handle that amount of work. ”


As Florida was cleaning up the wreckage left by Charley, Hurricane Frances made landfall on the state’s east coast on Sept. 5 as a Category 2 storm with winds up to 110 mph and sea surges of 6 to 8 feet. Frances knocked out power throughout Palm Beach County, and more than 40 gravity sewer lift stations were shut down.


“One of our vacuum stations is housed in a building that can withstand a Category 5 hurricane and is equipped with a back-up generator,” explained Robert Campbell, vacuum system technician for the Village of Palm Springs, Fla.  “We didn’t have to do anything [to the vacuum station]; it had been running since the power went out.” The village’s other vacuum station did not have backup power, but it was back on line quickly   once a portable generator was brought in.


The third storm, Ivan, a Category 3 hurricane, came ashore on Sept. 16 near Mobile, Ala.,  racking the Florida panhandle with high winds and rain. National Weather Service warnings provided some time to prepare, but most public works departments lacked the manpower and resources to get everything secured before the storm hit.  Those with vacuum systems benefited because they had backup electrical power to eliminate service interruptions.


“Our vacuum stations required zero preparation before the storm hit, so this allowed us to spend time on other things, like filling sand bags, anchoring street signs and so forth,” explained Thomas Voght, public works director in Cedar Grove, Fla., which is near Panama City.  “After the storm other cities had problems with their lift stations.  Cedar Grove was the only town in Bay County that didn’t experience any sewer problems.”


Sarasota County also took a glancing blow from Ivan, but Craig Bliss, manager, Water Reclamation Facilities of Sarasota County Utilities, said its vacuum sewers were unaffected. “We had very good success with our vacuum system during the hurricane.  The vacuum station required very little preparation and we never lost service in that area even though we lost electrical power. We currently have about 500 gravity lift stations.  That many lift stations require a significant amount of preparation before a storm hits and a lot of service afterward.”


The final storm to rumble into Florida was Hurricane Jeanne, packing 130 mph winds and sea surges up to 12 feet.  It made landfall on Sept. 25, less than 10 days after Ivan. Cities that had been hit by one or all of the preceding storms were still dealing with the cleanup efforts.


Palm Springs’ Campbell and his staff were overwhelmed with issues at their 40-plus gravity lift stations, but there were minimal problems from the vacuum sewers. “We had zero occurrences of sewage spilling on the ground from the vacuum systems,” said Campbell.  “Basically it was because of the holding capacity of the valve pits and the sealed system.  Other municipalities were, understandably, allowing sewage to flow onto the ground because they had no power.”


According to James Moore, assistant water superintendent of Carrabelle, one of Florida’s panhandle cities, “Other than checking the fuel and oil in the backup power units, the vacuum sewers required none of our time during and after the storms. The system had no downtime and continued to service our customers.”


Although vacuum stations are two to three times more costly than a lift station, replacing seven or eight gravity lift stations with one vacuum lift station reduces total system costs by about 20 percent to 25 percent, according to AIRVAC. From a design perspective, vacuum sewer systems are similar to gravity systems, however, engineers must take into account that vacuum systems have a hydraulic limit, which is a function of elevation, flow, and pipe length (see Figure 1).


Gradually, several Florida communities are expanding the use of vacuum sewer systems. For example, the Englewood Water District installed its first vacuum system in 1996 and continues to expand the number of stations and customers served. Sarasota County Utilities currently is installing vacuum sewer systems throughout the county. “When the project is complete we will have more than 20 new vacuum stations to service about 30,000 homes.” Said Bliss.  “That will mean a lot fewer headaches for us the next time a hurricane comes through.”

 

Advantages of vacuum sewers in Hurricanes


This article appeared in the April 2005 issue of CE News. 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 AIRVAC vacuum sewer installation in Englewood, Florida can be found in our Municipal Project Gallery.



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