Hydrogeochemical and clogging issues with ASR of reclaimed water in the brackish Werribee aquifer near Melbourne, Australia

“As part of an Integrated Water Cycle Management Strategy for the fast growing city of Melbourne, City West Water is conducting research to apply Aquifer Storage Recovery (ASR) utilizing recycled water. This non-potable water is injected and stored during winter in a brackish, anoxic sand aquifer at 220-240 m BGL, and recovered during peak demands in summer.
Hydrogeochemical issues consist of: (i) mobilization of trace metals and arsenic by pyrite oxidation; (ii) eutrophication due to high concentrations of NO3 and PO4, (iii) the formation of trihalomethanes and haloacetic acids by chlorination; (iv) the behavior of organic micropollutants in the aquifer; and (v) the
undesired admixing of ambient groundwater (TDS, H2S, natural radionuclides). In this contribution, we address the measured and predicted water quality changes of recycled water, during storage and recovery in the ASR well, and when passing a monitor well at 40 m distance.
Geochemical inspection of aquifer cores reveals that the main reactivity of the rather pure quartz sand consists of pyrite and organic material (partly as coal). Their slow reactivity is confirmed by the observed minor water quality changes during relatively short ASR cycles (6-50 days), comprising some O2, NO3, PO4, Zn and TCA reduction and little SO4, As and TIC production. Reactive transport modeling of the quality changes during future longer ASR cycles showed significantly more water-sediment interaction.”

(Citaat: Stuyfzand, P.J., Osma, J. – Hydrogeochemical and clogging issues with ASR of reclaimed water in the brackish Werribee aquifer near Melbourne, Australia – ISMAR 10, Madrid, Spain, 20-24 May 2019, p.104)