International Review of Waste Management Policy - Department of ...

include up to 150 substances including halogenated organics, organo-sulphur
compounds and aromatic hydrocarbons depending on the nature of the waste. 1229
The gases which are emitted in any one year are assumed to be related to the
quantity of methane or CO2 produced, depending upon whether one is considering
raw gas or gas once combusted (Table 63-8). Methane emissions to the atmosphere
and methane emissions captured are both used to estimate, on a proportional basis,
emissions of different trace gases in a given year using the relative composition of
gas outlined in below. The way this is done is to normalise the concentrations (by
weight) so that:
995
� Where gas is flared, the emissions of other gases are calculated with
reference to the studies by Enviros et al and White et al. The way this is done
is by calculating the CO2 content of flared gas and calculating the emissions of
other gases through the quantities relative to CO2 as specified in the two
studies mentioned;
� A similar approach is used to calculate fugitive emissions, but in this case, the
other emissions are calculated relative to the calculated quantity of methane
emissions; and
� For gas which is emitted from the gas engine, the emissions of other gases are
calculated using the quantities estimated in other studies relative to
calculated CO2 emissions.
There are some inconsistencies in this approach, the principal one being that the
White et al data make little allowance for changes in the level of oxidation of methane
through the cap of the landfill site. Our model incorporates this as a variable. It is
important to appreciate here that oxidation may appear not only at the cap (and
typical estimates in the literature are 10%), but also in the leachate, so that total
oxidation of methane to carbon dioxide may be greater than is sometimes suggested.
Landfills produce less of the pollutants for which dose response functions are
tolerably well known. No external damage costs have therefore been developed for
many of pollutants listed in Table 63-8. Externalities associated with the non
greenhouse gas air pollutants result in damage costs totalling €4.92 per tonne of
landfilled waste under the high externalities, or €2.07 if the lower values are
assumed. These figures include impacts associated with the use of diesel at the
facility, and a small amount of avoided emissions resulting from the generation of
electricity from landfill gas.
1229 Komex (2002) Investigation of the Composition and Emissions of Trace Components in Landfill
Gas, R&D Technical Report P1-438/TR for the Environment Agency, Bristol.
International Review of Waste Policy: Annexes