The site-based application of MAGIC requires data for each site on a range of physical and chemical properties. Site specific data input to the model include annual rainfall and runoff volumes, deposition chemistry, and soil depth, bulk density, porosity and cation exchange capacity (CEC). The model is calibrated to eight measured 'target variables'; surface water concentrations of the base cations calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K), and soil exchangable fractions of the same ions.
Of the 1573 sites originally sampled, 236 couldn't be used for modelling due to lack of input data. Cl and SO4 fluxes for the remaining 1337 sites were checked for potential internal sources of these 'conservative ions'. This led to an exclusion of a further 350 sites, predominantly in lowland areas such as the Midlands and East Anglia.