CEN/TS 17685-4:2026

Earthworks - Chemical tests - Part 4: Determination of soluble sulphate (in water) content in soils

Publication date:   Aug 6, 2026

Scope

The purpose of this document is to describe a test for the determination of water-soluble sulphate content in a soil sample (WS), by initial dissolution in demineralized water and subsequent precipitation with a saturated barium chloride (BaCl2) solution, according to the following reaction:

The presence of multi-valent anions in soils, such as phosphates or oxalates, can interfere with the method as they are liable to co-precipitate with the BaCl2 solution, leading to a mass increase in the residue and a subsequent overestimation of the water-soluble sulphate content. Carbonates are excluded from this interference as they are removed as CO2 (g) through the preliminary addition of hydrochloric acid.
Annex B specifies a qualitative method for the rapid detection of water-soluble sulphates in soil by aqueous dissolution and subsequent precipitation with BaCl2.
Furthermore, Annex C provides a quantitative method for the determination of the gypsum (CaSO4·2H2O) content in a soil sample, derived from the non-gypsum water-soluble sulphate content previously determined.
The results obtained in accordance with this document do not represent the total sulphate content of the soil, but exclusively the fraction soluble in water under the specific conditions defined in this document. These results are not comparable with those obtained by CEN/TS 17685 5:2026, relative to the determination of water-soluble salt content in soils (WSS).