Airports, glycols in de-icing liquids and Heathrow local water pollution

There are two main water pollutants arising from the Heathrow site, glycol used for de/anti-icing activities and hydrocarbons from oil and fuel. On 15th December, before the heavy snow on 17th and 18th which closed the airport for several days, that ” Heathrow  had  500,000 litres of de-icing fluid at their disposal.” But the de-icing chemicals are not without their environmental problems, and if allowed to enter ground water or water courses, exert levels of  biological oxygen demand (BOD).


Heathrow water pollution incidents:

Heathrow Airport fined for causing death of hundreds of fish

By Dan Coombs

Uxbridge Gazette


Heathrow Airport has been fined £13,000 for causing the death of hundreds of fish in a nearby lake.

The Airport last week pleaded guilty to discharging pollutants into the Clockhouse
Lane Pits lake system near Bedfont in April 2008.

This caused oxygen to plummet, killing numerous stickleback, perch and tench,
and thousands more fish had to be relocated to an adjacent lake.

The airport uses a tunnel system allowing it to discharge surface water runoff
into the lake, but on this occasion the maximum lawful limits of pollutants was

The discharge contained glycol, a common ingredient of de-icing fluids, applied
to aeroplanes and runways during periods of cold weather at Heathrow, and it was
this which caused the death of the fish in the lake.

A spokesperson for the Environmental Agency described the effects on the fish
population as having a ‘devastating impact’ and caused a significant loss of revenue
for recreational companies working in and around the lake.

The airport paid £195,000 in compensation to the Princes Ski Club, who lease
the lake, for their loss of business, as it was forced to close for a week as
the clean-up took place.

The airport was also asked to pay £15,000 in court costs.



29.9.2010   (Water Briefing)       link


Company fined £40K for Heathrow groundwater pollution

A London company responsible for supplying jet fuel at Heathrow Airport was fined

£40,000 last week and ordered to pay the Environment Agency in excess of £14,000
for its costs, after severely polluting groundwater beneath the airport, with
at least 139,000 litres of Jet A-1 aviation fuel.

Heathrow Hydrant Operating Company Limited (HHOpCo), of 8 York Road, London SE1

had pleaded guilty at Uxbridge Magistrates’ Court in June this year to causing
polluting matter to enter the Taplow Gravels groundwater, contrary to section
85 (1) and (6) of the Water Resources Act 1991. The case had been committed to
Isleworth Crown Court for sentence.

The court heard that on 29 November 2007 HHOpCo informed the Environment Agency

of a leak in the fuel supply pipeline to aircraft stands at Heathrow’s Terminal
One building. The leak was discovered by HHOpCo nine days earlier following an
unrelated report from BAA about a report of jet fuel odour in a nearby access
tunnel. Without this unrelated report, it is not known how long the leak would
have continued to go undetected for. HHOpCo conducted an overnight pressure test
on the hydrant system and confirmed the leak, but failed to notify the Environment
Agency immediately.

On further investigation HHOpCo staff identified a valve chamber full of approximately
8,000 litres of aviation fuel. Once the valve chamber was emptied, fuel was seen
leaking out of one of the attachments on the hydrant. Two bolts on the attachment
were so badly corroded that they had caused the leak, which was estimated at the
time of discovery to flow at 10 litres of fuel per minute. A later estimate corrected
the leak to 7 litres per minute. It is not known how long the leak had been going
on for or the total volume of fuel lost.

All bolts and valves on that section of pipeline were subsequently replaced to
stop the leak. The section was pressure tested and returned to normal operation
the following morning. The chamber in question has now been decommissioned.

HHOpCo attended an interview under caution at the Environment Agency office on

the 12 March 2009. The company admitted during the interview that a £7 million
automated leak detection system had been malfunctioning at the time and had not
detected the leak. This was also indicated in HHOpCo’s investigation report, which
revealed that the leak detection system was not working for at least five months
prior to the Environment Agency being notified of the incident. The company did
not put a manual testing system in place despite knowing that the automated system
was not working properly.

It quickly became clear that jet fuel had been leaking for some time. A specialist

remediation company sank boreholes to recover fuel and remediate the affected
area. As at June 2010 139,391 litres have been recovered and is still being recovered
at a rate of 80—100 litres per week.   The cost of remediation to date is approximately
£1 million.

Mohammed Jama, the Environment Agency’s lead officer on the case, said:

“Heathrow Hydrant Operating Company’s carelessness has led to the extensive pollution of groundwater. Fortunately, to date, we have not seen any major impact to local rivers but jet fuel in groundwater has the potential to seriously harm the environment and water quality. The fine issued reflects the serious effect that HHOpCo’s failures have had on the Taplow Gravels.”

“Once groundwater becomes polluted it is very difficult to clean up. We hope that the fine issued will act as a prompt to HHOpCo and similar companies, reminding them of the importance of compliance and making sure that their actions do not cause harm to or damage the environment.”

HHOpCo’s contractors have been in charge of remediation and monitoring of the
fuel plume and continue to provide updates to the Environment Agency.





Company  fined £40K for Heathrow groundwater pollution   

29.9.2010 (due to oil spill, not de-icing fluid)

In the recent snowy and icy weather, immense volumes of de-icing liquids were
used on planes at our airports, with Gatwick and Heathrow using the most.   On
15th December, before the heavy snow on 17th and 18th which closed the airport
for several days, that ”  Heathrow now has 69 vehicles on its Snow Team, with 500,000 litres of de-icing fluid at their disposal.”

BAA’s Heathrow website says:     link

Water quality 

The activities that take place at Heathrow Airport, combined with snow and rainfall
contributions, generate water run-off to surface, foul and groundwater as well
as impacting on water consumption and flood risk.

These activities are a result of BAA Heathrow’s operations and those of our tenants,
customers, passengers and other third parties.

As the airport operator, in conjunction with our business partners we have an
important role to play in managing these water issues in a responsible and sustainable manner.

Businesses and individuals operating at the airport are responsible for following
BAA Heathrow policies and procedures as laid down in various documents including OSIs.



There are two aquifers running beneath Heathrow that flow in the lower chalk
aquifer from north-west to south-east and in the upper terraced gravels aquifer
generally flows towards the nearest rivers.

There are two main water pollutants arising from the Heathrow site, glycol used for de/anti-icing activities and hydrocarbons from oil and fuel. Other pollutants such as heavy metals do occur but with lower frequency and in significantly smaller quantities.

The activities associated with the sources of pollution are carried out by both BAA Heathrow directly, our tenants, customers and other third parties, and we must work together to reduce the risk of a pollution incident.


Activities that can lead to water pollution include:

  • De-icing activities of both aircraft and runways and taxiways
  • Aircraft fuel spills and other spills
  • Oils and chemical storage and use
  • Herbicide and pesticide storage and use
  • Fuel farm and fuel supply
  • Construction activities.

Foul water

Foul or trade effluent discharges arise as a result of work activities, this
is discharged through a foul sewage system to Mogden sewage treatment works in
south-west London, run by Thames Water.

A number of activities at Heathrow cannot be discharged to surface water and
require a trade effluent discharge consent. Examples of these activities include:

  • Effluent from aircraft washing
  • Effluent from vehicle and ground equipment washing
  • Effluent from stand, apron and runway cleaning
  • Effluent from aircraft sanitation
  • Effluent from fire training activities
  • Effluent from cleaning and maintaining the boiler plan




Wikipedia says, on de-icing aircraft:

On the ground, when there are freezing conditions and precipitation, de-icing an aircraft is crucial. Frozen contaminants cause critical control surfaces to be rough and uneven disrupting smooth air flow and greatly degrading the ability of the wing to generate lift and increasing drag. This situation can cause a crash. If large pieces of ice separate when the aircraft is in motion, they can be ingested in engines or hit propellers and cause catastrophic failure.

Frozen contaminants can jam control surfaces, preventing them from moving properly. Because of this potentially severe consequence, de-icing is performed at airports where temperatures are likely to be around 0 °C.

In flight, droplets of supercooled water often exist in stratiform and cumulus clouds. They form into ice when they are struck by the wings of passing airplanes and abruptly crystallize. This disrupts airflow over the wing, reducing lift, so aircraft that are expected to fly in such conditions are equipped with a de-icing system.

De-icing techniques are also employed to ensure that engine inlets and various
sensors on the outside of the aircraft are clear of ice or snow.

De-icing on the ground is usually done by spraying aircraft with a de-icing fluid based on propylene glycol, similar to ethylene glycol antifreeze used in some automobile engine coolants. Ethylene Glycol (EG) is still in use for aircraft de-icing
in some parts of the world because it has a lower operational use temperature
(LOUT) than PG, but Propylene Glycol (PG) is more common because it is classified
as non-toxic, unlike Ethylene Glycol. Nevertheless, it still must be used with
containment system to capture the used liquid, so that it cannot seep into the ground and water courses. Even though classified as non-toxic, it has negative effects in nature, since it uses oxygen during breakdown, causing aquatic life to suffocate.
In one case, a significant
snow in Atlanta in early January 2002 caused an overflow of such a system, briefly contaminating the Flint River downstream of the Atlanta airport. Many airports recycle used de-icing fluid, separating water and solid contaminants,
enabling reuse of the fluid in other applications.

There are several types of de-icing fluid, falling into two basic categories:

1. De-icing fluids -Heated glycol diluted with water for de-icing and snow/frost
removal, also referred to as
Newtonian fluids (owing to their viscous flow similar to water) and

2. Anti-icing fluid – unheated, undiluted propylene glycol based fluids that has been thickened (imagine half-set gelatin), also referred to as Non-Newtonian fluids (owing to their characteristic viscous flow), applied to retard the future development
of ice or to prevent falling snow or sleet from accumulating. Anti-icing fluids
provide holdover protection against the formation of ice while the aircraft is
stationary on the ground but when subjected to shearing force such as the air
flow over the fluid surface, an aircraft accelerating for take off – the fuids
whole reology changes and it becomes significantly thinner, running off to leave
a clean and smooth aerodynamic surface to the wing. In some cases both types of
fluid are applied, first the heated glycol/water mixture to remove contaminants,
followed by the unheated thickened fluid to keep ice from reforming before the
aircraft takes off. This is called “a two-step procedure”.

Methanol de-ice fluid has been employed for years to de-ice small wing and tail
surfaces of small to medium-sized general aviation aircraft and are usually applied
with a small hand-held sprayer. Methanol can only remove frost and light ground
ice prior to flight.

Mono-ethylene, di-ethylene and propylene glycol are nonflammable petroleum products and similar products are most commonly found in automotive cooling systems. Gylcol has very good de-icing properties and the aviation grade is referred to as SAE/ISO/AEA Type I (AMS 1424 or ISO 11075). it is usually applied to contaminated surfaces
diluted 50% with water at 95 degrees Fahrenheit using a cherry picker on a truck
containing 1500 to 2000 US Gallons (5680 to 7570 L) for on-ramp or departure runway
entry point application. Colour-dyed fluid is preferred as it can be confirmed
easily by visual observation that an aircraft has received a de-ice. Run off Type
I appears to turn slush a pink tinge hence the term pink snow. Otherwise, all
Type I fluids are orange.

and it continues …………… link      



(extract ….)
by ~Mark Liner, PE, Senior Engineer, Naturally Wallace Consulting
….     Although the glycols typically used for deicing are readily treatable,
creating a steady state of predictable flow and concentration for treatment is
an engineering challenge. 

Saying that there is a best available technology for glycol treatment at airports
is like saying there is a best available spouse for a marriage. What works in
one case is not necessarily going to work in another. The means of treatment must
be coupled with the unique traits of the airport’s stormwater management program
to develop a sound and workable relationship.

Regulating bodies worldwide are working to address deicing practices at airports
and these efforts are the catalyst for airport management to update, enhance,
or install new treatment systems that will better protect the environment. In
the US, the Environmental Protection Agency proposed new rules in 2009 that will
effectively level the playing field by creating a national standard to which all
airports must comply. The challenge US airports face is how to comply with these
new regulations in a cost-effective, responsible manner.

&lquot;There are four key areas to consider when treating deicing runoff,&rquot; comments
Scott Wallace, P.E., president of
Naturally Wallace Consulting (NWC). &lquot;The varying nature of winter storms, the type of deicing chemicals applied,
effective nutrient addition, and the need for safe airfield operations all have
to be factored in to any treatment design.&rquot;

A wide range of practices are currently used by airports for management of spent
deicing fluids. Technologies range from sophisticated recycling units to simple
aerated lagoons. The systems reflect the deicing activity of the airport in which
they are installed and are tailored for the climate and air traffic.

Technical Challenges

Most deicing areas are constructed to provide quick drainage as reflected by
the pipes and drains around an airport. Though necessary for keeping gates and
pads free of ponding water, this &lquot;flush and forget&rquot; approach results in the potential
for downstream flooding. To combat this, airports have incorporated stormwater
storage tanks, vaults, and ponds to shave peak flows. With large airfields producing
significant runoff, stormwater storage volumes can be massive and are typically
sized in the millions of gallons.

Though effective at buffering peak flows, these large storage volumes are not
usually piped to capture the initial first flush of a storm. This is the period
of time that generally contains the largest concentrations of pollutants. Civil
engineers are increasingly aware of this and are incorporating front-end quality
control volumes into stormwater management systems. The dirty, first flush that
is captured is pulled aside during a storm event and treated.

Glycol Treatment Using Engineered Wetlands

The environmental effects of deicing fluids are mostly related to the high oxygen
demand they exert when released to rivers and streams. If the oxygen supply in
the river or stream runs out, the water turns anaerobic – resulting in fish kills
and plant upsets.

The magnitude of the deicing fluid wastewater aspects should not be dismissed.
A gallon of propylene glycol (PG) has roughly 8 pounds of oxygen demand. To put that in some perspective, each of us flush about 0.2 pounds of oxygen demand down the toilet each day. Another way of putting it is that one gallon of PG per day is equivalent to 40 people in wastewater terms.
Since we have been building domestic sewage plants for over 30 years, we have
a good idea how much the new ones cost: between $3,000 to 9,000 in capital costs
per pound of oxygen demand per day. Using the same metric, each gallon of glycol
used per day has a capital cost in the range of $24,000 to $72,000. Considering
that over 200 gallons of PG can be used per plane for deicing, you can imagine
how the numbers and impact on the environment begin to pile up.

Using engineered wetlands have proven to be an efficient and effective treatment
solution. Engineered wetland treatment systems provide a simple and robust treatment process that can be ramped up or down to meet varying treatment demands with minimal time demands from airfield operations staff. Engineered wetland treatment systems of deicing fluid have been adopted by airports in the United States, Canada, and the United Kingdom.

In the past, passive wetland systems had difficulty in handling the kind of high
strength effluents that result from airport deicing operations. Using Forced Bed
AerationTM (FBA) a technology patented by NWC, engineered wetland systems can
be created that are capable of overcoming the oxygen transfer limitations of conventional treatment wetlands. This is key in treating industrial wastewater including deicing runoff. FBA uses forced air at low pressure in a controlled system to enhance the ability to treat contaminants and handle increases in hydraulic load. In tests at Heathrow Airport, the FBA system produced a ten fold increase in treatment
compared to control beds. With FBA the ability to use natural treatment solutions
expanded dramatically to the point that nearly any organic contaminant can now
be treated using the aerobic biological treatment approach. In addition, the efficiency
of treatment using an FBA system allows for a smaller system footprint in most
cases along with lower lifecycle costs including maintenance and power usage.

Completed NWC airport deicing projects using engineered wetlands, include an
award-winning subsurface flow engineered wetland system at Buffalo Niagara International
Airport (NY) that treats up to 6 million gallons daily of stormwater laden with
deicing fluid. Currently the NWC team is engaged in the expansion of the existing
deicing fluid treatment wetland system at the Edmonton International Airport (Canada)
and at Heathrow (UK). NWC is also on the project team to design an aerated gravel
bed using NWC’s patented Forced Bed AerationTM to treat deicing fluid at Macarthur
Airport in Islip, Long Island (NY).

Propylene glycol has very low toxicity to humans
However, it has serious environmental effects on bodies of water, lowing their
oxygen concentration.
EnvironmentalPropylene glycol is known to exert high levels of biochemical oxygen demand (BOD) during degradation in surface waters. This process can adversely affect
aquatic life by consuming oxygen aquatic organisms need to survive. Large quantities
dissolved oxygen (DO) in the water column are consumed when microbial populations decompose ethylene
The oxygen depletion potential of airport deicing operation discharges is many
times greater than that of raw sewage. For example, before application, Type I
propylene glycol-based deicing fluid is generally diluted to a mixture containing
approximately 50% propylene glycol. Pure propylene glycol has a five-day biochemical
oxygen demand (BOD5) concentration of approximately 1,000,000 mg/L. A typical
diluted propylene-based deicing fluid could therefore have a BOD5 concentration
of approximately 500,000 mg/L. In comparison, raw sewage typically has a BOD5
concentration of approximately 200 mg/L. The amount of fluid used to deice a single
jet depends on the nature of the precipitation event and the size of the aircraft
but can range from several hundred to several thousand gallons. Therefore, deicing
a single jet can generate a BOD5 load greater than that of one million gallons
of raw sewage. A large hub airport often has several hundred flights each day.
Sufficient DO levels in surface waters are critical for the survival of fish,
macroinvertebrates, and other aquatic organisms. If oxygen concentrations drop
below a minimum level, organisms emigrate, if able and possible, to areas with
higher oxygen levels or eventually die. This effect can drastically reduce the
amount of usable aquatic habitat. Reductions in DO levels can reduce or eliminate
bottom-feeder populations, create conditions that favor a change in a community’s
species profile, or alter critical food-web interactions
Water Link international
7.12.2010   says
Completed NWC (Naturally Wallace  Consulting)  airport deicing projects include
a subsurface flow engineered wetland system at Buffalo Niagara International Airport
(NY) that treats 1.2 million gallons of stormwater laden with deicing fluid every
day. In addition to the EIA project, currently the NWC team is engaged by the
British Airport Authority to design a deicing fluid remediation system for Heathrow
Airport in conjunction with ARM, Ltd (UK).

The Environment Agency says:


Pollution Prevention: Private, commercial and military airfields.




De-icers are used to prevent the formation of ice and to remove ice, frost or
snow from
vulnerable hard surfaces and aircraft to enable the safe movement of aircraft,
vehicles and

Conventional de-icers such as granular salt cannot be applied to runways or aircraft
of their corrosive nature and alternative materials such as prilled urea or glycols
or calcium
magnesium acetate are substituted. De-icers may also contain dewetting and thickening
agents to increase the effectiveness of the operation. The fluid concentration
will be
increased as the ambient temperature drops. Records should be kept by airport
authorities and
individual users of de-icer consumption.

Many independent carriers at commercial sites will carry out the de-icing of
their own aircraft.  
This activity normally occurs just before take-off and may involve up to 1000
litres of solution
to deice one large aircraft. The use of vacuum equipment to remove excess fluid
from the
hardstanding around the aircraft may be beneficial, as this will reduce the polluting
entering the drainage system. Fluid remaining on the aircraft will normally be
deposited on the
runway during take off.

Runway and taxiway de-icing can occur at any time as conditions dictate, and
increasingly probable as temperatures fall below 4
oC. De-icing chemicals are normally dispensed by specialist vehicles. Storage facilities are either 200 litre drums,
bulk containers
or fixed sites. Mixing and heating facilities may be prior to loading of spraying
vehicle or as
part of the equipment. The bunding of tank and drum storage will be required.


Most airlines have de-icing procedures and usage documentation, with the operation
carried out by company personnel or contracted out.     Details of the de-icing agents and their use will normally be taken into account
by the Agency
when considering discharge consents. The Agency should be notified of the type
and quantity
of de-icer used on a regular basis, which will depend on local circumstances
and may be daily,
weekly or monthly.



a report by  the Parliaments Office for Science and Technology, April 2003, states
(page 42):


Aviation and the environment


De-icing at airports


Snow, ice or slush on aircraft and runways can result in hazardous conditions
that can lead to accidents,
delays, diversions and cancellations. In general, airlines are responsible for
the de-icing and anti-icing of
aircraft and airports are responsible for the de-icing of runways and airfields.

Globally, chemicals such as ethylene or propylene based glycol mixtures, containing between 10 and 20 percent
additives, are the most
common methods of de-icing and anti-icing, with approximately 300-400 gallons
of de-icing/anti-icing fluid
used per aircraft. BAA airports do not use ethylene glycol for de-icing.   Additives,
such as dioxane,
formamides, and acetaldehyde, among other chemicals, can be used as wetting agents,
corrosion inhibitors,
surfactants, dyes and thickeners. Estimates have suggested that at least 80%
of the de-icer/anti-icer chemicals
applied to aircrafts do not remain on the aircraft but spill onto the ground
or spray into the atmosphere.

De-icing and anti-icing chemicals can contaminate groundwater and surface water
supplies if allowed to flow
from airport facilities to storm drains or waterways. Ethylene and propylene
glycol based chemicals are very
soluble and can rapidly breakdown in a process that consumes oxygen and threatens
aquatic life.

Urea-based de-icing agents are also frequently used and, when released into the
environment, increase the
nitrate content of soil. As with glycol based de-icing/anti-icing chemicals,
urea based chemicals reduce the
oxygen levels of water resources and can be directly or indirectly toxic to aquatic
organisms. Although nitrate
pollution from airports is not comparable with the nitrate pollution caused by
agriculture, it can lead to
significant local pollution. Nitrates are harmful to humans when they enter the
human body because they are
converted into the carcinogenic nitrosamine.

To comply with pollution control regimes in the UK, airport operators must minimise
and control potential
water pollution from de-icing. Thus, they use tanks or ponds to hold run-off
so that it can be released during
high flow periods, when mixing of the runoff with high water volumes minimises
effects on aquatic systems.

Many airport operators filter the runoff through equipment that removes the pollutants.
Other methods include
de-icing pads, the use of vacuum sweeper trucks to capture de-icing or anti-icing
chemicals and the use of a
common stormwater system, sanitary sewer system or another dedicated drainage
system. Another option is
to use less harmful chemicals or techniques for de-icing/anti-icing operations,
such as potassium acetate or
calcium magnesium acetate which have no significant impact on water quality.

In the US one airline is testing a system based on forced air and a smaller amount of de-icing fluid, which requires
half the amount of de-icing
fluid than previously. Another airline is using a new method for de-icing aircraft
that uses an infrared
technology inside a hangar. This technique is still in its early stages of development
but at present appears too
slow to be of use at busy airports.

April 2003



Water World     link  says:

Demonstration Testing – Heathrow, Airport – Deicing Fluid

Spent deicing fluid from Heathrow Airport in London, England, is collected and
sent to nearby Mayfield Farm for treatment. The treatment system is composed of
aerated lagoons and constructed wetlands. Aeration of the existing subsurface
wetland beds was undertaken in 2009 so as to demonstrate the effect on treatment.
Three of the existing beds were tested in parallel. The first bed was unmodified,
the second bed was re-piped to a vertical flow configuration, and the third bed
was reconfigured like bed number two and also aerated.

Results from the full-scale demonstration test clearly illustrate the benefits
of aeration. Removals of chemical oxygen demand (COD) are consistent and directly
associated with the level of aeration in the beds. Second to the proof of performance,
the full scale modifications also provided valuable information with respect to
constructability and the level of effort required to modify the existing asset
to improve performance.