LandGEM uses the following first-order decomposition rate equation to estimate annual:

where

Q_CH4 = annual methane generation in the year of calculation (m³/year)

i = 1 year time increment

n = (year of the calculation) - (initial year of waste acceptance)

j = 0.1 year time increment

k = methane generation rate (year^-1) 

L_o = potential methane generation capacity (m³/t)

M_i = mass of waste accepted in the i^th year (t)

t_ij = age of the j^th section of waste mass M_i accepted in the i^th year (decimal years, e.g. 3.2 years)