Water flow and storage in fractured, unsaturated sulphur blocks

Water is a primary control on the generation of acidic (H 2 SO 4 ) effluent from commercial-scale sulphur (S 0 ) blocks. Although clean S 0 is strongly hydrophobic, microbial colonization of fracture faces and friable S 0 generates localized hydrophilic conditions. Infiltration occurs preferentially along discrete fractures and in areas of friable S 0 . Surface evaporation rates are low (mean 0.2 mm/day), and >90% of rainfall infiltrates and rapidly drains from the blocks. A conceptual model to describe the flow and storage of water at the base of S 0 blocks was developed and tested. The S 0 blocks were represented as a hydrophilic equivalent porous medium, and lateral drainage through the base of the blocks was quantified using a two-dimensional numerical model. Specific yield (S y ) and saturated hydraulic conductivity (K s ) values were estimated to be ∼4%–7% and ∼1 × 10 −2  m/s, respectively, by comparing measured and modelled pore-water pressure head and outflow responses to rainfall events. Given that commercial-scale S 0 blocks are constructed in a similar manner worldwide, the results of this study are considered widely applicable in designing S 0 block storage facilities that minimize water availability and H 2 SO 4 production in S 0 blocks.