Geochemical modelling and laboratory experiments to test the feasibility of artificial recharge

摘要

Chemical reactions may influence the success of artificial recharge and subsurface water storage schemes. Primary concerns are deterioration of water quality and clogging effects. Geochemical evaluation was required for a feasibility study involving a a planned borehole injection scheme in the semi-arid Western Karoo, South Africa. A breccia pipe has been identified as a potential underground repository for emergency water supplies. Geochemical modelling was used to simulate pH-buffering effects and solute activity changes across a mixing front during injection of various recharge sources. Saturation indices for carbonate and ferric iron minerals were then used to predict whether the formation fo precipitates would be thermodynamically favoured. Modelling was supplemented by laboratory leaching tests to identify readily soluble components in the aquifer materials, and by water-rock equilibration batch tests, which assessed the capacity for aquifer rocks to sorb and immobilise dissolved species from a range of recharge waters.