Total molar fraction of the organic contaminant, defined as
X^c=\frac{S_LN_Lx^c_L+(1-S_L)N_Gx^c_G}{S_LN_L+(1-S_L)N_G},
where S_L and S_G are the liquid and gas phase saturatons, N_L and N_G are the liquid and gas phase molar densities, x^c_L and x^c_G are the contaminant molar fractions in the liquid and gas phases.
Used in no end-to-end test cases.