The potential of riverbank filtration for drinking water supplies in relation to microsystin removal in brackish aquifers

In semi-arid areas, pumping town water supplies from alluvium adjacent a stream rather than the stream itself has been used to reduce turbidity and has potential to remove blue-green algal toxins, such as microsystin. However for some rivers, such as the River Murray in South Eastern Australia, the ambient groundwater of unconfined aquifers skirting some reaches of the river is saline. This paper examines the compatibility of two constraints on the quality of water recovered from bank filtration schemes; that (1) removal of cyanobacterial toxins is adequate and (2) salinity is acceptable for drinking water supplies. Adsorption and biodegradation characteristics of a cyanobacterial hepatotoxin, microsystin, in porous media were quantified and these results are summarised in the current analysis. It was found that riverbank filtration schemes could meet both criteria in a limited range of conditions, excluding locations where saline groundwater discharges to a river. However, on a river meander that had been flushed due to a hydraulic gradient induced by a lock, several feasible positions for bank filtration wells were compared and a best location meeting salinity and microsystin criteria with least-energy pumping cost was identified. The simple approach developed is intended to be used to assess feasibility of alternative designs for bank filtration schemes in semi-arid areas before commencing field studies.