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).