In other words, the percentages of SO2−4 HCO−3 are not summed, but rather are represented by
choosing the ion present in higher percentage (e.g., the Na-HCO3/SO4 facies can represent both the Na-HCO3 facies and the Na-SO4 facies). If there is water of both facies then the sample will be represented using the percentage of bicarbonate (if %HCO−3 > %SO2−4 ) or sulfate (if %SO2−
4 > %HCO−3 ), and this will be indicated in the center of the diagram using different symbols. The result is a representation of 4 heterotopic facies (Na-HCO3, Na-Cl, Ca-HCO3, and Ca-Cl) out of 16 facies (or 6 out of 24 facies if one takes into account that sulfate and bicarbonate water can coexist).