Kh = hydraulic conductivity
i = hydraulic gradient
d = mixing zone depth
I = infiltration rate
L = axial length of source
rb = soil density
Kd = sorption coefficient
ne = porosity
Xirv = irreversibly sorbed fraction
k2 = degradation constant
x = distance to receptor
v = groundwater velocity
There are some exceptions to this, for example, when insoluble contaminant-containing solids are likely to form. See the technical guidance document for details, as well as for sources of the various default parameters used in the calculation.