\(F_{Fw,SK1}\ for\ contaminant\ A=\ F_{Fw,SK1}\text{\ for\ contaminant\ B\ }\) (4)
\(F_{Fw,SK1}=\operatorname{}{\sum_{i=1}^{I}{F_{SRi,SKj}\left[\frac{{(C_{k,SRi}-C_{k,Fw})}}{\left(C_{k,SRi_{s}}-C_{k,Fw}\right)}-1\right]}+F_{\text{SKj}}\left[1-\frac{(Z_{k,SKj}-C_{k,Fw})}{\left(C_{k,SRi_{s}}-C_{k,Fw}\right)}\right]}\) (5)