The standard deviation sum-of-fractions for surface soil is calculated as follows:
\begin{equation} S_{\text{sof}} = \sqrt{(\frac{S_1}{DCGL_1})^2 + (\frac{S_2}{DCGL_2})^2 + etc.}\end{equation}
Where the Derived Concentration Guidance Levels (DCGL) are known and the standard deviations (\(S\)) values are estimated for each nuclide.