ABSTRACT
The hydraulic and salinity response to aquifer storage and recovery of a highly saline, unconfined, permeable limestone aquifer, and a deep confined low permeability limestone aquifer are discussed. A town water supply is being developed in a highly saline unconfined highly transmissive limestone aquifer, in a location where toxic algae make river water non potable during summer. The injection of 890 ML over five cycles developed a ‘sacrificial lens’ with a radius beyond 145 m. Trial recovery through the 1997/98 summer indicated the scheme could deliver 20 ML of UV sterilised, filtered potable water. Clogging has not been shown to be a problem to date. Water will need to be injected to sustain the ‘sacrificial lens’ during the year, and prior to summer to ensure sufficient storage. An irrigation scheme has been developed in a saline deep confined low transmissivity limestone aquifer. A volume of 75 ML of storm water was pressure injected at a rate of 8 L/s with an injection head of-70 m. During repeated cycles of injection, followed by backflushing, the specific capacity increased indicating dissolution close to the well. Recovery indicated 40% with storm water salinity, 90% less than 1,000 mg/L, 100% less than 1,300 mg/L. These examples in carbonate aquifers indicate the difference in injecting and recovering water from a confined low transmissivity aquifer where the injected ‘bubble’ remains localised with little decay, and from an unconfined high transmissivity aquifer where the injected lens decays rapidly.
