The physical weathering of calcium and magnesium strata will contribute cations to surface and ground water. Dissolved cations are carried via overland, unsaturated, or saturated flow. EDTA forms a chelated soluble complex when added to metal cations. Dye added creates a wine-red solution. EDTA added as a titrant complexes with the Ca and Mg.
Solution turns blue when all complexed.
Varies according to modifications of technique. Suspended or colloidal organic matter may interfere.