The second step is to classify the sinks into Above and Below Pinch regions, for both contaminants ’A’ and ’B’. The source order for contaminant ’A’ is: SR1->SR2->SR3-SR4, while the source order for ’B’ is: SR4->SR3->SR2-SR1.
The required step is to compute the ratio of shifted sink concentration to the shifted source concentration (Z*k,SKj/C*k,SRi) for each sink-source pair and for each contaminant ’k’. Table 4 shows the computation results. For SK1 and SK3, as all the minimum ratios paired with SR1, SR2, SR3 and SR4 are less than 1, they are impossible to be fulfilled by merely internal sources. This is because the concentrations (either A or B) of these sources are all higher than both of the sinks. For SK3, although SR2 has lower concentrations of A and B than SK3, the source flowrate is not enough to cover SK3. So, they require freshwater and should be classified as Below the Pinch in contaminant ’A’ Composite Curve. While for SK2 and SK4, the minimum ratios for both sinks to all sources are less than 1, which means they should be classified as sinks that belong to below the Pinch Region.
Table 4: Determination of sink-to-source concentration ratio. The minimum value among the contaminants are highlighted in bold