Assessing the risks of deep injection of treated wastewater into an aquifer for storage and reclamation

Abstract

Characterising behaviour of a particular liquid material injected into an aquifer is fraught with uncertainties and unknowns due to a multiplicity of factors. These include the sub-surface environment, the quality of the material to be injected, its behaviour during and after injection. Knowledge is required not only of the geological and chemical characteristics of the aquifer such as the profile of any existing native liquid material, but of the natural ecology of the soil into which product is to be injected and specific details of the composition of the liquid. Neither the soil nor the product for injection should be assumed to be inert or sterile. Some relationships between geological, chemical and microbiological constituents will occur if only though dint of close contact and the nature of these interactions needs understanding if, as in the instance of artificial injection, a change in existing natural conditions is involved. Storage and reuse of wastewater for the growing metropolis of Sydney has been suggested as a way of capturing and reusing wastewater currently being disposed through ocean outfalls. The present paper examines some of the concerns in the deep injection of treated wastewater for reclamation-reuse purposes. This technology, termed aquifer storage and recovery (ASR) has already been tested in a 5- year experiment at the Andrews Farm site on the North Adelaide Plains of South Australia (Barry et al, 2002). The current paper in particular, focuses on three aspects of using ASR for water conservation purposes in the Sydney region. The approach is: (i) an overview of geological data on Sydney region comparing two hypothetical sites - the Bald Hill Claystone and the Botany Sands aquifer (ii) attention to issues of a hydrogeochemical and microbiological nature that could impact on groundwater in an aquifer if deep injection of wastewater is undertaken; and (iii) foreshadowing methods which could be used to learn more about.