There is provided a computer assisted method for obtaining a pollution type model for hydrocarbon pollutions of soil, and to use such a pollution type model to determine the pollution type apportionment of a soil sample. There is also provided a computer assisted method for obtaining a corrected GC-FID chromatogram of a soil sample comprising one or more hydrogen compounds, wherein the correction of the chromatogram includes an adjustment of the chromatogram for retention time related changes in the sensitivity of the GC-FID system, and wherein the adjustment may be performed by use of a produced data set. Furthermore, there is provided a computer assisted method for producing a data set for adjusting GC-FID (gas-chromatography/flame ionization detector) chromatograms for retention time related changes in the sensitivity of the GC-FID system. In addition, there is provided a computer assisted method for producing a number of calibration curves to be used in determining total hydrocarbon concentrations of soil samples from GC-FID chromatograms, and there is provided a computer assisted method for determining the total hydrocarbon concentrations by use of GC-FID chromatograms and the produced calibration curves.