Deicing by Design
Cleveland gets a new pad.
An airport runway is the most important mainstreet in any town.—Norman Crabtree, Former Director, Ohio Department of Transportation
Snow Day
Reveling in a mean annual snowfall of 55 inches, Cleveland, OH, is accustomed to snow and ice, in vast quantities. On a typical winter morning it is not unusual for many Cleveland residents to find themselves beginning the day dusting light snow, or scraping a bit of frost, from their vehicles’ windshields before heading off to work. A few miles away, however, at Cleveland Hopkins International Airport, the picture can often be quite different. “Our issue is we are right on Lake Erie,” says Heidi Pruess, environmental manager for the Cleveland Airport System. “One of the things a meteorologist will tell you is that we frequently get something called lake effect precipitation. Winter storms that come across Lake Erie from Canada—if the lake is not frozen, which does happen every now and then—pick up that moisture, and we get a very heavy, wet snow.” On a typical winter morning at Cleveland Hopkins International Airport, the complex procedure known as aircraft deicing can be witnessed in full swing.
A Class of Its Own
Of the many less-than-pleasant winter tasks that keep things moving through the coldest months of the year, aircraft deicing is in a class of its own. Passengers packed shoulder to shoulder muse silently over the prospect of missing their connections while the distinctive but indescribable odor of glycol vapor permeates the cabin. Through the window, they can observe technicians in cherry pickers mounted on service vehicles spraying a steaming fluid through the cold, damp morning air over the plane’s various parts. Pilots, managers, agents, and controllers adjust taxiway and gate assignments in an attempt to maintain an orderly flow of takeoffs and landings, as the flight crew tries to provide reassurance and beverages to nervous passengers. All the while, hundreds of gallons of aircraft deicing fluid course over wings, tail, and fuselage and pour onto the tarmac.
At the completion of the process, there is no guarantee that an actual takeoff will occur; in fact, if conditions warrant and the delay before eventual takeoff extends beyond the specified holdover period for the particular deicing product, the entire process must sometimes be repeated, leaving thousands more gallons of aircraft deicing fluid (ADF)–contaminated stormwater streaming over the pavements.
At Cleveland Hopkins International Airport, says Pruess, “The deicing season stretches to six months out of the year.”
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Photo: Cleveland Hopkins Airport |
| Installation of underdrain on deicing pad during construction |
Objective: Safety
Although he is charged with ensuring environmental quality, Paul Anderson, a biologist and environmental specialist with the Ohio EPA, Northeast District, acknowledges that safety practices and their environmental consequences have evolved over time, though not always in tandem. He speculates that before the development of deicers and safety technology, “Pilots would have probably avoided flying in bad weather.” On the other hand, he says, most major airports were constructed prior to environmental regulation. But advances in technology, while widening the threshold for safe air travel, have sometimes brought safety and environmental concerns into conflict. “The safety of the aircraft always trumps environmental concerns,” he says. But he adds, “Now we’re trying to find ways to maintain aircraft safety as well as environmental quality.”
Ice Contamination
After a number of accidents attributed to the accumulation of ice on the exterior surfaces of aircraft, the Federal Aviation Administration (FAA) concluded that flying with ice on the aircraft posed an unacceptable safety hazard. Studies have shown that an icy coating as thin as one-sixty-fourth of an inch could have a significant effect on the aerodynamic qualities of the wing surface, reducing lift by 12% to 24%. Though the FAA does not mandate any particular deicing procedures, it strictly prohibits the takeoff of any aircraft with ice contamination This excerpt from an FAA notice provides guidance and clarification to aviation safety inspectors:
... under Title 14 of the Code of Federal Regulations sections 121.629(c) and 135.227(b). The regulations clearly state “no person may take off an aircraft when frost, ice, or snow is adhering to the wings …” and further in (section 121.629(b)) “… no person may dispatch, release or take off an aircraft any time conditions are such that frost, ice, or snow may reasonably be expected to adhere to the aircraft …” (section 121.629(c).
According to Pruess, on occasions when ice contamination might reasonably be expected, it is the pilots’ responsibility to make a visual inspection of the exterior of the aircraft. If ice is detected on any critical surface, it must be removed before takeoff. To detect clear ice, which may sometimes occur, the FAA recommends inspection by touch, by either the pilot or other responsible party. Pruess says the airport also compiles data provided by the National Weather Service and from sensors located around the facility to assess the risk of ice formation. She says pilots and applicators generally take a conservative approach to the issue and would prefer to err on the side of deicing more often, rather than less often, than necessary.
The EPA estimates that during typical wet-weather conditions, 150 to 1,000 gallons of ADF may be used on a single commercial jet, while a much smaller volume, as little as 10 gallons, may be used on a small corporate jet. An estimated 1,000 to 4,000 gallons may be needed to deice a commercial jet during severe weather conditions. However, ice formation is also a concern during dry weather, even at temperatures as high as 55 degrees Fahrenheit, says Pruess. “At times when frost would not be present on your car, frost may occur on an aircraft.” For instance, frost sometimes appears after landing on the wings of aircraft that have been supercooled during high-altitude flights. According to the EPA, dry-weather deicing requires 20 to 50 gallons of deicing fluid, depending on the size of the aircraft.
Two basic formulations are commonly used for ADFs; one is based on propylene glycol and the other on ethylene glycol. Though a trend has developed in the industry to phase out the more expensive and more toxic ethylene glycol, Pruess says that applicators, at their discretion, generally use either or both. In accord with the airport’s Publicly Owned Treatment Works (POTW) permit, she says, Cleveland Hopkins allows only the propylene-glycol-based ADF to be used.
Like antifreeze, ADFs work by depressing the freezing point of the water with which they are mixed in solutions up to 50%. For application, they are sometimes heated to 180 degrees Fahrenheit before being sprayed under pressure onto the exterior surfaces of the aircraft to either melt the ice that may have formed there or it knock off by force. The higher the glycol concentration of the ADF-water mixture, the lower the freezing point can be depressed. A 60% ethylene glycol and 40% water mix can attain a freezing point as low as 58 degrees below zero Fahrenheit. The minimum freeze point for propylene glycol ADFs is lower, at minus 75 degrees, but occurs at a higher glycol concentration.
Anti-icing fluids known as type IV fluids are applied after deicing; they are more viscous and are designed to adhere to the aircraft. Their purpose is to prevent new ice from forming while the aircraft awaits takeoff. They can hold out against ice for up to 70 minutes, depending on weather conditions and the specific formula. Anti-icing fluids are believed to shear away from the aircraft at what is called rotation, the aeronautical term for the moment the nose gear lifts from the runway during takeoff.
According to the EPA, 21 million gallons of ADF of 50% glycol concentration are applied to aircraft each year in the United States. The EPA estimates that when dilution by melting ice, snow, and rainwater during application is considered, aircraft deicing procedures yield 7 billion gallons of ADF-contaminated stormwater nationwide each year.
Mixed Toxicity
According to the EPA, ethylene glycol and propylene glycol are relatively nontoxic to aquatic organisms. Ethylene glycol, the chemical commonly used in automobile antifreeze, is fairly nontoxic to mammals except when ingested. In that instance, ethylene glycol has the potential to cause neurological, cardiovascular, and gastrointestinal problems; serious birth defects; and even death when the dosage is large enough. Propylene glycol, by contrast, does not exhibit direct toxicity. In fact, propylene glycol is often used as a food additive, humectant, and skin moisturizer and can be found in many consumable and topical preparations for human use.
According to a 2003 study published in Environmental Science & Technology, the US Geological Survey (USGS) has found that the pure glycols, when formulated for ADF, are often blended with other constituents such as surfactants, flame retardants, and corrosion inhibitors. These additives are proprietary and therefore have not yet been examined comparatively. Nevertheless, the USGS found alkyphenol ethoxylate surfactants used in ADF, as well as one of their breakdown products, nonyphenol, a known endocrine disruptor, in streams receiving airport runoff. Additionally, the USGS has begun to study the toxicity of glycols when combined in the environment with other reactive chemicals used in deicing fluids.
However, the dominant concern regarding ADF pollution has been the extremely high biological oxygen demand resulting from their major constituent, glycols, being released into the environment. As glycols break down in the aquatic environment, they deplete dissolved oxygen, resulting in fish kills and encouraging the growth of undesirable bacteria.
EPA Scrutiny
A survey of airfield environmental conditions published in 1996 by the Natural Resources Defense Council found that “45 of the 50 busiest airports in the country were within three miles of an ocean, bay, lake, wetland, reservoir, river, or stream.” Cleveland Hopkins fits squarely into this trend. The airfield covers an area of 1,900 acres in close proximity to Rocky River. Draining into Lake Erie, Rocky River is a favorite trout-fishing haven and one of the Cleveland Metropolitan Park system’s most popular attractions. Pruess says the airport has “two outfalls that discharge directly into the Rocky River within less than a mile—one within less than a quarter-mile. So we’re basically on the cliff overhanging the river.” Abrams Creek, a tributary to the Rocky River, runs directly through the airport property and had to be contained within an underground culvert to accommodate one of the airport’s runways. For decades, unregulated stormwater discharges from the airport have caused periodic complaints from park visitors of fish kills and noxious odors.
The Ohio EPA began negotiating with Cleveland Hopkins International more than a decade ago over pollution issues related to cold-weather operations of a different kind: pavement deicing.
“The major issue in those days,” says the EPA’s Anderson, “was urea, which was used to deice the runways. Urea, when it decomposes, turns into ammonia, and ammonia nitrogen in water can be extremely toxic to fish and other aquatic organisms. We were seeing fish kills and violations of our ammonia water-quality standards in both Abrams Creek and the Rocky River on flushes coming out from the airport during snowmelt.”
Additionally, aircraft deicing was being performed at the terminal gate, which, he says, was the standard for the industry at the time. “All the paved surfaces from the airport drained into the storm drains, so there were numerous complaints regarding odors. At times there would be bikers and walkers down in the park, and you’d get this incredible stench coming out of these storm drains. Then of course we’d have to worry about the glycol pollution of the river.”
The Ohio EPA filed a lawsuit against the City of Cleveland and the airport, culminating in a consent decree that was signed to remedy those issues in 1992. As part of the agreement, the airport was required not only to investigate and remediate the ammonia issue, which was resolved in part by switching to a different chemical for deicing of the runway, but also to look for ways to reduce pollution levels from other airfield procedures, including aircraft deicing.
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Photo: Cleveland Hopkins Airport |
| Deicing pad under construction |
A Slow Start
A celebration in 2005 marked Cleveland Hopkins’ 80th anniversary. As the oldest municipal airport in the United States, its festivities honored a tradition of aviation firsts, among them the first runway lights, first air traffic control tower, and first passenger terminal. However, like numerous aging airports across the country, Cleveland Hopkins has kept pace with more recent technological innovations through numerous iterations of retrofits. These intermarriages of old and new infrastructure made slow going of the investigatory work required by the consent decree to find the sources of pollution. Much of the focus, says Anderson, was “finding out what systems connected with what and where the problems were originating.” And he says for a long time little progress was made. “The airport was missing all of their compliance deadlines. As a result, in 2001, the agreement had to be renegotiated with new targets just to get the process back on track.” The Ohio EPA also issued the airport its first-ever stormwater permit. The permit required the airport to perform weekly sampling, to develop a cleanup plan, to control stormwater, and to identify and control pollutant discharges by a November 1, 2004, deadline.
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Photo: Meredith Brothers |
| Cellular containment structure installation under the pad |
Gear Up Clean Up
One advantage Cleveland Hopkins had was ambition. At the same time airport officials were looking for ways to reduce pollution levels, they were also considering a plan to expand the capacity of the airport’s hub operations. Pruess says a major catalyst in addressing the ADF issue turned out, in fact, to be the airport expansion program. Continental Airlines had selected Cleveland Hopkins as a location for its Midwest hub operations. Successful operation as a hub would require logistical coordination of banks of arrivals and departures. Any interruption or delay in the flow of air traffic could detrimentally affect both the profitability and the reputation of the airlines involved, the viability of the airport, and the reputation of the city itself. The project was designed to lengthen existing runways and to add a new runway parallel to an existing one. These improvements would facilitate nearly simultaneous landings and takeoffs from the airfield. Construction on the expansion project was completed in 2003.
“Adding the new runway changed the capacity of the airport from 45 planes per hour being able to take off to 55 to 60 planes per hour being able to take off,” says Mark Vilem, acting administrator of engineering for the Cleveland Airport System. “That means you have more flights coming in and out, and if you’re deicing all around the gate, you’re slowing down the ability of incoming planes to get to the gate. Occasionally, you’ll end up sitting out on a taxiway somewhere because they don’t have a gate open for you, because they’re waiting for the other planes to leave.” For a hub operation on very precise timetables, this kind of uncertainty could be a significant disadvantage.As construction was proceeding on the expanded runways, the airport had begun to experiment with a glycol collection system. The system entailed physically blocking the storm drains at the surface and collecting the spent ADF with glycol recovery vehicles (GRVs). “It’s essentially a vacuum system, like a street sweeper but without the sweeper,” says Pruess. She says the airport was able to collect millions of gallons per year from the surface. The system, however, had disadvantages.
“It requires a lot of maintenance; the GRVs have pretty powerful vacuums, and they pull up joint seal in the pavement. The glycols themselves migrate through the pavement and get into the pavement system.” She says these problems demonstrate why “it is not as efficient to collect from the surface as to collect from a lined collection system beneath the pavement.” Though she says the GRV system has proven effective in capturing a significant portion of the glycols, she did not believe it be a viable solution to the glycol issue for the long term. “It was not one of the options, because that is the way we were doing it currently and we were not fully meeting the permit requirements.”
Evaluating the Alternatives
An option the airport did explore was installation of an onsite wastewater treatment facility. This POTW treatment plant would have collected and treated all fluid from the airport. Pruess says evaluation of this option revealed that due to the sheer volume of surface-area runoff the airport would be required to treat, the plant would need to be larger than the Northeast Ohio Regional Sewer District treatment plant that treats the entire Cleveland area. That plan proved impractical, says Pruess. “There were space limitations and budget limitations for doing something of that scale and size. The other issue with deicing fluids is because you only use them six months out of the year, the treatment facility would have to go down and up and down and up each year, which is not very conducive to adequate treatment in a system like that.” In fact, she says, “We would have to feed the wastewater plant—we would be looking for people who needed to discharge things so we would have water to keep the plant alive.”
To Build or Not to Build
The airport put together a deicing committee made up of the deicing contractors, the airlines, and the city, as the property owner, to discuss issues related to aircraft deicing. From the start, says Pruess, “They all agreed on a couple of things; one is that they don’t want to be burdened, that they want to get as many aircraft off the airport as possible, and that deicing should not be a hindrance to their schedule. But of course they’re competitors of one another, so there were several issues that needed to be worked out.” One of the first accomplishments they worked out was an agreement to perform deicing at specific areas rather than right at the gate, in order to facilitate more efficient collection.
Once it was decided that the airport was going to implement a deicing pad, it took the better part of two years of meeting after meeting to iron out the details of how the airlines would access the deicing pads, how their aircraft would be handled on the pads, and then understanding movement off the deicing pad. “It was a very long negotiation and there are a lot of details that are involved,” says Pruess. “Each airline has their own set of operating procedures, which do not necessarily match the others, of course, so all those issues had to be reconciled.” There were concerns about fuel costs for airliners that would need to taxi to and from the gate to the deicing area. But Anderson notes, “The centralized deicing pad became more and more attractive as time went on, because it allowed for better cost control for the deicing process.”
There were differences. According to Bill Barley of R.W. Armstrong, the engineering firm that developed the project, some of the smaller carriers were concerned that a centralized deicing pad could be monopolized by the major hub carrier; the major carriers had worries that the small carrier deicing practices would impede their hub operations. Everyone wondered who would get priority status if a queue were to develop at the pad.But Barley says the dialogue was always cordial and professional between the airlines as they worked out preliminary arrangements to implement the pad. “Everybody had their own concerns, but it never got overly contentious,” he says. “The reality was everybody had the same concerns—how to make deicing as painless as possible.” He credits Heidi Pruess and Cleveland Hopkins staff with creating and managing an atmosphere of collaboration among the stakeholders during these discussions, and he says many of the issues that arose were resolved in the design phase. For instance, the pad was configured with enough capacity to absorb peak hub operations. It was designed with two rows of deicing bays to keep traffic flowing, and an auxiliary pad is being implemented at a remote location to accommodate and segregate smaller aircraft used for the more frequent regional jet traffic.
Barley says, “As corporate citizens, the airlines understand their role as environmental stewards.” But he says, they were all also aware that “if there were any fines for noncompliance against the airport, the costs would eventually be passed through to the tenants.”
The Pad
“Its hard to imagine how big an area we’re talking about until you’ve been out there,” says Vilem. The pad encompasses 28 acres for deicing and overspray, and an additional 10 acres of taxiway. It can accommodate three group 5 aircraft such as 747s or Airbuses, or 12 group 2 or 3 aircraft such as 737s or regional-type jets seating 40 to 50 passengers. After 13 months of construction, at a cost of about $40 million, the pad will become operational in the fall of 2006.
“We’re building it right in kind of a triangle between three major taxiways to get the planes from the concourse to the runways, so we’re constantly surrounded by moving aircraft while we’re working,” says Vilem. “We have to be careful how we cross the taxiway to get into the construction site. Sometimes we’ve had 100 construction workers at a time out there. When we’re pouring concrete we’ll have 40 or 50 semi trucks driving back and forth to the concrete plant and coming back to the site to put concrete down in front of the paving machine, so there’s a lot of activity and a lot of coordination.”
Perched Waters
One of the challenges faced by the design team and the construction crew was dealing with the unique geology of the area where the pad was to be situated. Vilem says the geology was formed by glaciers coming through thousands of years ago; the shale bedrock is relatively impermeable, so any surface water does not percolate readily to the water table. “We have largely clay soil, but there’s sand lenses throughout the area, so you get spots where there’s just a bunch of water in the ground, kind of isolated pockets here and there. During construction, you make certain assumptions about the ground,” he says, “but all of a sudden you hit a pocket which is all sand and full of water and muck—horrendously wet—and 5 feet away it’s perfectly dry.”
Barley says R.W. Armstrong designed cellular containment structures to stabilize the soil while allowing for the free movement of water during construction. Barley and his team collaborated with the cellular confinement (Geoweb) manufacturer, Presto Products Co., its consulting engineers, and Ohio distributor Meredith Brothers to analyze the project details and determine the best solution utilizing this technology.
“The Geoweb system develops a structurally stable aggregate drainage system for groundwater and supports the impervious membranes that prevent the possibility of groundwater contamination,” says Presto Products Geosystems’ Daniel Senf, P.E. “Using the Geoweb system eliminates the need for excessive excavation while increasing structural capacity, which saves construction costs. In addition, Geoweb stabilizes aggregate so it can handle the heavy loads of construction and commercial aircraft.”
The prominence of perched water also necessitated another of the pad’s distinctive engineering features. “One of the unique things we did was to design a dual underdrain system for the deicing pad,” says Pruess. “There’s an underdrain below the liner for any water that might come up from underneath to keep that system drained so that it doesn’t impact the structure of the pavement above it. Then there’s an underdrain above that liner that will continually collect the surface runoff from the pad itself. The idea of the dual underdrain system is to keep the clean water clean. The impacted water will be collected for disposal or treatment, and the clean water underneath will go directly to the storm system.”
The drainage piping also got special consideration during design and construction. The question was what material to use to conduct the impacted runoff from the spent fluid. There were drawbacks to using either concrete or metal piping to handle contaminated fluids. “We stayed away from concrete; it works well for storm systems but not for contaminated collection systems,” says Vilem. “Concrete always leaks, just by its nature; there’s an allowable leakage rate. We didn’t want either clean water coming in, which we then would have to treat, or the impacted water getting out. We did a fairly extensive analysis and came up with using high-density polyethylene piping.” Pruess adds, “Testing has been done at each phase of construction just to make sure everything is connected properly.”
In many ways, however, says Barley of R.W. Armstrong, the pad is intentionally low tech. For instance, he says, “We looked at using fixed-boom applicators, but we felt, based on the configuration and the fact that it is not a land-rich airport, we wanted the flexibility that mobile applicators would give us. With this system, when the pad is not being used for deicing, it can serve as overnight parking for aircraft. In summer months, when construction may be taking place elsewhere at the airport, two of the bays become through taxiways.”
Water-quality monitoring within the system will also be done manually through sampling performed by the collection contractor. As opposed to an automated system, this will give the collection contractor the flexibility to decide when to open the storm drain valves or route the runoff for treatment. It also gives the contractor the option, if the glycol concentrations are sufficiently high, to route the ADF-contaminated runoff to storage tanks for later recycling. The point, says Barley, was to build in flexibility to accommodate what can be foreseen but not to overbuild or underbuild.
Vilem says he expects the infrastructure to perform over a lifespan of at least 20 to 30 years. Barley thinks the design is flexible enough to accommodate any changes in fleet composition or technology that are likely to emerge in the foreseeable future.
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Barley believes the pad will be successful and attributes his optimism to the collaborative effort that resulted in a project acceptable to all of the stakeholders—including, he believes, the passengers. “From the time you leave your gate ’til the time you take off, you don’t want to spend a half-hour waiting; you want to be able to get out, get done, and get off the ground,” he says. “I don’t think you could ever say deicing a plane is a pleasing experience, but we try to make it as efficient as possible.”
As winter weather approaches Cleveland, Heidi Pruess will be looking forward to putting that efficiency to the test. “Anytime you try something for the first time, you have to anticipate that things are not going to be perfect. We’re going to plan for as many things as we can plan for, but we’ll be massaging the system, I’m sure. How the aircraft gets to the pad, how the applicator of the fluid conducts its business, how the collection contractor most efficiently runs through their task for ultimate disposal of the fluid—all that will be massaged as we go through the first year.”Pruess adds, “We also have a plan for collection of data at a series of points within that system so we can see the efficiency of collection. We have collection on the upstream side and the downstream side—that should be very revealing. The deicing pad and the type of collection system that we are creating is estimated to be more efficient than what is required to meet our permit obligations. If that holds true,” she says, “then that was the best option for everyone.”
Author's Bio: David C. Richardson is a journalist based in Baltimore, MD.
October 2006
Deicing by Design
Cleveland gets a new pad.
An airport runway is the most important mainstreet in any town.—Norman Crabtree, Former Director, Ohio Department of Transportation
Snow Day
Reveling in a mean annual snowfall of 55 inches, Cleveland, OH, is accustomed to snow and ice, in vast quantities. On a typical winter morning it is not unusual for many Cleveland residents to find themselves beginning the day dusting light snow, or scraping a bit of frost, from their vehicles’ windshields before heading off to work. A few miles away, however, at Cleveland Hopkins International Airport, the picture can often be quite different. “Our issue is we are right on Lake Erie,” says Heidi Pruess, environmental manager for the Cleveland Airport System. “One of the things a meteorologist will tell you is that we frequently get something called lake effect precipitation. Winter storms that come across Lake Erie from Canada—if the lake is not frozen, which does happen every now and then—pick up that moisture, and we get a very heavy, wet snow.” On a typical winter morning at Cleveland Hopkins International Airport, the complex procedure known as aircraft deicing can be witnessed in full swing.
A Class of Its Own
Of the many less-than-pleasant winter tasks that keep things moving through the coldest months of the year, aircraft deicing is in a class of its own. Passengers packed shoulder to shoulder muse silently over the prospect of missing their connections while the distinctive but indescribable odor of glycol vapor permeates the cabin. Through the window, they can observe technicians in cherry pickers mounted on service vehicles spraying a steaming fluid through the cold, damp morning air over the plane’s various parts. Pilots, managers, agents, and controllers adjust taxiway and gate assignments in an attempt to maintain an orderly flow of takeoffs and landings, as the flight crew tries to provide reassurance and beverages to nervous passengers. All the while, hundreds of gallons of aircraft deicing fluid course over wings, tail, and fuselage and pour onto the tarmac.
At the completion of the process, there is no guarantee that an actual takeoff will occur; in fact, if conditions warrant and the delay before eventual takeoff extends beyond the specified holdover period for the particular deicing product, the entire process must sometimes be repeated, leaving thousands more gallons of aircraft deicing fluid (ADF)–contaminated stormwater streaming over the pavements.
At Cleveland Hopkins International Airport, says Pruess, “The deicing season stretches to six months out of the year.”
|
Photo: Cleveland Hopkins Airport |
| Installation of underdrain on deicing pad during construction |
Objective: Safety
Although he is charged with ensuring environmental quality, Paul Anderson, a biologist and environmental specialist with the Ohio EPA, Northeast District, acknowledges that safety practices and their environmental consequences have evolved over time, though not always in tandem. He speculates that before the development of deicers and safety technology, “Pilots would have probably avoided flying in bad weather.” On the other hand, he says, most major airports were constructed prior to environmental regulation. But advances in technology, while widening the threshold for safe air travel, have sometimes brought safety and environmental concerns into conflict. “The safety of the aircraft always trumps environmental concerns,” he says. But he adds, “Now we’re trying to find ways to maintain aircraft safety as well as environmental quality.”
Ice Contamination
After a number of accidents attributed to the accumulation of ice on the exterior surfaces of aircraft, the Federal Aviation Administration (FAA) concluded that flying with ice on the aircraft posed an unacceptable safety hazard. Studies have shown that an icy coating as thin as one-sixty-fourth of an inch could have a significant effect on the aerodynamic qualities of the wing surface, reducing lift by 12% to 24%. Though the FAA does not mandate any particular deicing procedures, it strictly prohibits the takeoff of any aircraft with ice contamination This excerpt from an FAA notice provides guidance and clarification to aviation safety inspectors:
... under Title 14 of the Code of Federal Regulations sections 121.629(c) and 135.227(b). The regulations clearly state “no person may take off an aircraft when frost, ice, or snow is adhering to the wings …” and further in (section 121.629(b)) “… no person may dispatch, release or take off an aircraft any time conditions are such that frost, ice, or snow may reasonably be expected to adhere to the aircraft …” (section 121.629(c).
According to Pruess, on occasions when ice contamination might reasonably be expected, it is the pilots’ responsibility to make a visual inspection of the exterior of the aircraft. If ice is detected on any critical surface, it must be removed before takeoff. To detect clear ice, which may sometimes occur, the FAA recommends inspection by touch, by either the pilot or other responsible party. Pruess says the airport also compiles data provided by the National Weather Service and from sensors located around the facility to assess the risk of ice formation. She says pilots and applicators generally take a conservative approach to the issue and would prefer to err on the side of deicing more often, rather than less often, than necessary.
The EPA estimates that during typical wet-weather conditions, 150 to 1,000 gallons of ADF may be used on a single commercial jet, while a much smaller volume, as little as 10 gallons, may be used on a small corporate jet. An estimated 1,000 to 4,000 gallons may be needed to deice a commercial jet during severe weather conditions. However, ice formation is also a concern during dry weather, even at temperatures as high as 55 degrees Fahrenheit, says Pruess. “At times when frost would not be present on your car, frost may occur on an aircraft.” For instance, frost sometimes appears after landing on the wings of aircraft that have been supercooled during high-altitude flights. According to the EPA, dry-weather deicing requires 20 to 50 gallons of deicing fluid, depending on the size of the aircraft.
Two basic formulations are commonly used for ADFs; one is based on propylene glycol and the other on ethylene glycol. Though a trend has developed in the industry to phase out the more expensive and more toxic ethylene glycol, Pruess says that applicators, at their discretion, generally use either or both. In accord with the airport’s Publicly Owned Treatment Works (POTW) permit, she says, Cleveland Hopkins allows only the propylene-glycol-based ADF to be used.
Like antifreeze, ADFs work by depressing the freezing point of the water with which they are mixed in solutions up to 50%. For application, they are sometimes heated to 180 degrees Fahrenheit before being sprayed under pressure onto the exterior surfaces of the aircraft to either melt the ice that may have formed there or it knock off by force. The higher the glycol concentration of the ADF-water mixture, the lower the freezing point can be depressed. A 60% ethylene glycol and 40% water mix can attain a freezing point as low as 58 degrees below zero Fahrenheit. The minimum freeze point for propylene glycol ADFs is lower, at minus 75 degrees, but occurs at a higher glycol concentration.
Anti-icing fluids known as type IV fluids are applied after deicing; they are more viscous and are designed to adhere to the aircraft. Their purpose is to prevent new ice from forming while the aircraft awaits takeoff. They can hold out against ice for up to 70 minutes, depending on weather conditions and the specific formula. Anti-icing fluids are believed to shear away from the aircraft at what is called rotation, the aeronautical term for the moment the nose gear lifts from the runway during takeoff.
According to the EPA, 21 million gallons of ADF of 50% glycol concentration are applied to aircraft each year in the United States. The EPA estimates that when dilution by melting ice, snow, and rainwater during application is considered, aircraft deicing procedures yield 7 billion gallons of ADF-contaminated stormwater nationwide each year.
Mixed Toxicity
According to the EPA, ethylene glycol and propylene glycol are relatively nontoxic to aquatic organisms. Ethylene glycol, the chemical commonly used in automobile antifreeze, is fairly nontoxic to mammals except when ingested. In that instance, ethylene glycol has the potential to cause neurological, cardiovascular, and gastrointestinal problems; serious birth defects; and even death when the dosage is large enough. Propylene glycol, by contrast, does not exhibit direct toxicity. In fact, propylene glycol is often used as a food additive, humectant, and skin moisturizer and can be found in many consumable and topical preparations for human use.
According to a 2003 study published in Environmental Science & Technology, the US Geological Survey (USGS) has found that the pure glycols, when formulated for ADF, are often blended with other constituents such as surfactants, flame retardants, and corrosion inhibitors. These additives are proprietary and therefore have not yet been examined comparatively. Nevertheless, the USGS found alkyphenol ethoxylate surfactants used in ADF, as well as one of their breakdown products, nonyphenol, a known endocrine disruptor, in streams receiving airport runoff. Additionally, the USGS has begun to study the toxicity of glycols when combined in the environment with other reactive chemicals used in deicing fluids.
However, the dominant concern regarding ADF pollution has been the extremely high biological oxygen demand resulting from their major constituent, glycols, being released into the environment. As glycols break down in the aquatic environment, they deplete dissolved oxygen, resulting in fish kills and encouraging the growth of undesirable bacteria.
EPA Scrutiny
A survey of airfield environmental conditions published in 1996 by the Natural Resources Defense Council found that “45 of the 50 busiest airports in the country were within three miles of an ocean, bay, lake, wetland, reservoir, river, or stream.” Cleveland Hopkins fits squarely into this trend. The airfield covers an area of 1,900 acres in close proximity to Rocky River. Draining into Lake Erie, Rocky River is a favorite trout-fishing haven and one of the Cleveland Metropolitan Park system’s most popular attractions. Pruess says the airport has “two outfalls that discharge directly into the Rocky River within less than a mile—one within less than a quarter-mile. So we’re basically on the cliff overhanging the river.” Abrams Creek, a tributary to the Rocky River, runs directly through the airport property and had to be contained within an underground culvert to accommodate one of the airport’s runways. For decades, unregulated stormwater discharges from the airport have caused periodic complaints from park visitors of fish kills and noxious odors.
The Ohio EPA began negotiating with Cleveland Hopkins International more than a decade ago over pollution issues related to cold-weather operations of a different kind: pavement deicing.
“The major issue in those days,” says the EPA’s Anderson, “was urea, which was used to deice the runways. Urea, when it decomposes, turns into ammonia, and ammonia nitrogen in water can be extremely toxic to fish and other aquatic organisms. We were seeing fish kills and violations of our ammonia water-quality standards in both Abrams Creek and the Rocky River on flushes coming out from the airport during snowmelt.”
Additionally, aircraft deicing was being performed at the terminal gate, which, he says, was the standard for the industry at the time. “All the paved surfaces from the airport drained into the storm drains, so there were numerous complaints regarding odors. At times there would be bikers and walkers down in the park, and you’d get this incredible stench coming out of these storm drains. Then of course we’d have to worry about the glycol pollution of the river.”
The Ohio EPA filed a lawsuit against the City of Cleveland and the airport, culminating in a consent decree that was signed to remedy those issues in 1992. As part of the agreement, the airport was required not only to investigate and remediate the ammonia issue, which was resolved in part by switching to a different chemical for deicing of the runway, but also to look for ways to reduce pollution levels from other airfield procedures, including aircraft deicing.
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Photo: Cleveland Hopkins Airport |
| Deicing pad under construction |
A Slow Start
A celebration in 2005 marked Cleveland Hopkins’ 80th anniversary. As the oldest municipal airport in the United States, its festivities honored a tradition of aviation firsts, among them the first runway lights, first air traffic control tower, and first passenger terminal. However, like numerous aging airports across the country, Cleveland Hopkins has kept pace with more recent technological innovations through numerous iterations of retrofits. These intermarriages of old and new infrastructure made slow going of the investigatory work required by the consent decree to find the sources of pollution. Much of the focus, says Anderson, was “finding out what systems connected with what and where the problems were originating.” And he says for a long time little progress was made. “The airport was missing all of their compliance deadlines. As a result, in 2001, the agreement had to be renegotiated with new targets just to get the process back on track.” The Ohio EPA also issued the airport its first-ever stormwater permit. The permit required the airport to perform weekly sampling, to develop a cleanup plan, to control stormwater, and to identify and control pollutant discharges by a November 1, 2004, deadline.
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Photo: Meredith Brothers |
| Cellular containment structure installation under the pad |
Gear Up Clean Up
One advantage Cleveland Hopkins had was ambition. At the same time airport officials were looking for ways to reduce pollution levels, they were also considering a plan to expand the capacity of the airport’s hub operations. Pruess says a major catalyst in addressing the ADF issue turned out, in fact, to be the airport expansion program. Continental Airlines had selected Cleveland Hopkins as a location for its Midwest hub operations. Successful operation as a hub would require logistical coordination of banks of arrivals and departures. Any interruption or delay in the flow of air traffic could detrimentally affect both the profitability and the reputation of the airlines involved, the viability of the airport, and the reputation of the city itself. The project was designed to lengthen existing runways and to add a new runway parallel to an existing one. These improvements would facilitate nearly simultaneous landings and takeoffs from the airfield. Construction on the expansion project was completed in 2003.
“Adding the new runway changed the capacity of the airport from 45 planes per hour being able to take off to 55 to 60 planes per hour being able to take off,” says Mark Vilem, acting administrator of engineering for the Cleveland Airport System. “That means you have more flights coming in and out, and if you’re deicing all around the gate, you’re slowing down the ability of incoming planes to get to the gate. Occasionally, you’ll end up sitting out on a taxiway somewhere because they don’t have a gate open for you, because they’re waiting for the other planes to leave.” For a hub operation on very precise timetables, this kind of uncertainty could be a significant disadvantage.As construction was proceeding on the expanded runways, the airport had begun to experiment with a glycol collection system. The system entailed physically blocking the storm drains at the surface and collecting the spent ADF with glycol recovery vehicles (GRVs). “It’s essentially a vacuum system, like a street sweeper but without the sweeper,” says Pruess. She says the airport was able to collect millions of gallons per year from the surface. The system, however, had disadvantages.
“It requires a lot of maintenance; the GRVs have pretty powerful vacuums, and they pull up joint seal in the pavement. The glycols themselves migrate through the pavement and get into the pavement system.” She says these problems demonstrate why “it is not as efficient to collect from the surface as to collect from a lined collection system beneath the pavement.” Though she says the GRV system has proven effective in capturing a significant portion of the glycols, she did not believe it be a viable solution to the glycol issue for the long term. “It was not one of the options, because that is the way we were doing it currently and we were not fully meeting the permit requirements.”
Evaluating the Alternatives
An option the airport did explore was installation of an onsite wastewater treatment facility. This POTW treatment plant would have collected and treated all fluid from the airport. Pruess says evaluation of this option revealed that due to the sheer volume of surface-area runoff the airport would be required to treat, the plant would need to be larger than the Northeast Ohio Regional Sewer District treatment plant that treats the entire Cleveland area. That plan proved impractical, says Pruess. “There were space limitations and budget limitations for doing something of that scale and size. The other issue with deicing fluids is because you only use them six months out of the year, the treatment facility would have to go down and up and down and up each year, which is not very conducive to adequate treatment in a system like that.” In fact, she says, “We would have to feed the wastewater plant—we would be looking for people who needed to discharge things so we would have water to keep the plant alive.”
To Build or Not to Build
The airport put together a deicing committee made up of the deicing contractors, the airlines, and the city, as the property owner, to discuss issues related to aircraft deicing. From the start, says Pruess, “They all agreed on a couple of things; one is that they don’t want to be burdened, that they want to get as many aircraft off the airport as possible, and that deicing should not be a hindrance to their schedule. But of course they’re competitors of one another, so there were several issues that needed to be worked out.” One of the first accomplishments they worked out was an agreement to perform deicing at specific areas rather than right at the gate, in order to facilitate more efficient collection.
Once it was decided that the airport was going to implement a deicing pad, it took the better part of two years of meeting after meeting to iron out the details of how the airlines would access the deicing pads, how their aircraft would be handled on the pads, and then understanding movement off the deicing pad. “It was a very long negotiation and there are a lot of details that are involved,” says Pruess. “Each airline has their own set of operating procedures, which do not necessarily match the others, of course, so all those issues had to be reconciled.” There were concerns about fuel costs for airliners that would need to taxi to and from the gate to the deicing area. But Anderson notes, “The centralized deicing pad became more and more attractive as time went on, because it allowed for better cost control for the deicing process.”
There were differences. According to Bill Barley of R.W. Armstrong, the engineering firm that developed the project, some of the smaller carriers were concerned that a centralized deicing pad could be monopolized by the major hub carrier; the major carriers had worries that the small carrier deicing practices would impede their hub operations. Everyone wondered who would get priority status if a queue were to develop at the pad.But Barley says the dialogue was always cordial and professional between the airlines as they worked out preliminary arrangements to implement the pad. “Everybody had their own concerns, but it never got overly contentious,” he says. “The reality was everybody had the same concerns—how to make deicing as painless as possible.” He credits Heidi Pruess and Cleveland Hopkins staff with creating and managing an atmosphere of collaboration among the stakeholders during these discussions, and he says many of the issues that arose were resolved in the design phase. For instance, the pad was configured with enough capacity to absorb peak hub operations. It was designed with two rows of deicing bays to keep traffic flowing, and an auxiliary pad is being implemented at a remote location to accommodate and segregate smaller aircraft used for the more frequent regional jet traffic.
Barley says, “As corporate citizens, the airlines understand their role as environmental stewards.” But he says, they were all also aware that “if there were any fines for noncompliance against the airport, the costs would eventually be passed through to the tenants.”
The Pad
“Its hard to imagine how big an area we’re talking about until you’ve been out there,” says Vilem. The pad encompasses 28 acres for deicing and overspray, and an additional 10 acres of taxiway. It can accommodate three group 5 aircraft such as 747s or Airbuses, or 12 group 2 or 3 aircraft such as 737s or regional-type jets seating 40 to 50 passengers. After 13 months of construction, at a cost of about $40 million, the pad will become operational in the fall of 2006.
“We’re building it right in kind of a triangle between three major taxiways to get the planes from the concourse to the runways, so we’re constantly surrounded by moving aircraft while we’re working,” says Vilem. “We have to be careful how we cross the taxiway to get into the construction site. Sometimes we’ve had 100 construction workers at a time out there. When we’re pouring concrete we’ll have 40 or 50 semi trucks driving back and forth to the concrete plant and coming back to the site to put concrete down in front of the paving machine, so there’s a lot of activity and a lot of coordination.”
Perched Waters
One of the challenges faced by the design team and the construction crew was dealing with the unique geology of the area where the pad was to be situated. Vilem says the geology was formed by glaciers coming through thousands of years ago; the shale bedrock is relatively impermeable, so any surface water does not percolate readily to the water table. “We have largely clay soil, but there’s sand lenses throughout the area, so you get spots where there’s just a bunch of water in the ground, kind of isolated pockets here and there. During construction, you make certain assumptions about the ground,” he says, “but all of a sudden you hit a pocket which is all sand and full of water and muck—horrendously wet—and 5 feet away it’s perfectly dry.”
Barley says R.W. Armstrong designed cellular containment structures to stabilize the soil while allowing for the free movement of water during construction. Barley and his team collaborated with the cellular confinement (Geoweb) manufacturer, Presto Products Co., its consulting engineers, and Ohio distributor Meredith Brothers to analyze the project details and determine the best solution utilizing this technology.
“The Geoweb system develops a structurally stable aggregate drainage system for groundwater and supports the impervious membranes that prevent the possibility of groundwater contamination,” says Presto Products Geosystems’ Daniel Senf, P.E. “Using the Geoweb system eliminates the need for excessive excavation while increasing structural capacity, which saves construction costs. In addition, Geoweb stabilizes aggregate so it can handle the heavy loads of construction and commercial aircraft.”
The prominence of perched water also necessitated another of the pad’s distinctive engineering features. “One of the unique things we did was to design a dual underdrain system for the deicing pad,” says Pruess. “There’s an underdrain below the liner for any water that might come up from underneath to keep that system drained so that it doesn’t impact the structure of the pavement above it. Then there’s an underdrain above that liner that will continually collect the surface runoff from the pad itself. The idea of the dual underdrain system is to keep the clean water clean. The impacted water will be collected for disposal or treatment, and the clean water underneath will go directly to the storm system.”
The drainage piping also got special consideration during design and construction. The question was what material to use to conduct the impacted runoff from the spent fluid. There were drawbacks to using either concrete or metal piping to handle contaminated fluids. “We stayed away from concrete; it works well for storm systems but not for contaminated collection systems,” says Vilem. “Concrete always leaks, just by its nature; there’s an allowable leakage rate. We didn’t want either clean water coming in, which we then would have to treat, or the impacted water getting out. We did a fairly extensive analysis and came up with using high-density polyethylene piping.” Pruess adds, “Testing has been done at each phase of construction just to make sure everything is connected properly.”
In many ways, however, says Barley of R.W. Armstrong, the pad is intentionally low tech. For instance, he says, “We looked at using fixed-boom applicators, but we felt, based on the configuration and the fact that it is not a land-rich airport, we wanted the flexibility that mobile applicators would give us. With this system, when the pad is not being used for deicing, it can serve as overnight parking for aircraft. In summer months, when construction may be taking place elsewhere at the airport, two of the bays become through taxiways.”
Water-quality monitoring within the system will also be done manually through sampling performed by the collection contractor. As opposed to an automated system, this will give the collection contractor the flexibility to decide when to open the storm drain valves or route the runoff for treatment. It also gives the contractor the option, if the glycol concentrations are sufficiently high, to route the ADF-contaminated runoff to storage tanks for later recycling. The point, says Barley, was to build in flexibility to accommodate what can be foreseen but not to overbuild or underbuild.
Vilem says he expects the infrastructure to perform over a lifespan of at least 20 to 30 years. Barley thinks the design is flexible enough to accommodate any changes in fleet composition or technology that are likely to emerge in the foreseeable future.
Barley believes the pad will be successful and attributes his optimism to the collaborative effort that resulted in a project acceptable to all of the stakeholders—including, he believes, the passengers. “From the time you leave your gate ’til the time you take off, you don’t want to spend a half-hour waiting; you want to be able to get out, get done, and get off the ground,” he says. “I don’t think you could ever say deicing a plane is a pleasing experience, but we try to make it as efficient as possible.”
As winter weather approaches Cleveland, Heidi Pruess will be looking forward to putting that efficiency to the test. “Anytime you try something for the first time, you have to anticipate that things are not going to be perfect. We’re going to plan for as many things as we can plan for, but we’ll be massaging the system, I’m sure. How the aircraft gets to the pad, how the applicator of the fluid conducts its business, how the collection contractor most efficiently runs through their task for ultimate disposal of the fluid—all that will be massaged as we go through the first year.”Pruess adds, “We also have a plan for collection of data at a series of points within that system so we can see the efficiency of collection. We have collection on the upstream side and the downstream side—that should be very revealing. The deicing pad and the type of collection system that we are creating is estimated to be more efficient than what is required to meet our permit obligations. If that holds true,” she says, “then that was the best option for everyone.”