Water Journal : Water Journal July 2011
water JULY 2011 55 Water Quality and Water Safety A second group, led by Stuart Khan, addressed Water Quality and Water Safety issues. The issues identified covered both chemical water quality and microbial water quality. Depending on injection water sources and pre-treatment, a suite of natural and synthetic chemicals may be introduced to aquifers during MAR activities. The ultimate fate of these chemicals will be dependent upon their physical and chemical properties, but may include adsorption to solid materials, oxidation/reduction reactions, and aerobic or anaerobic biodegradation. Such processes will be both chemical- and aquifer-specific. However, the consensus of the group was that insufficient information is currently available to provide accurate predictions of chemical fate in most circumstances. Similarly, the need for a generic methodology for the validation of contaminant removal during aquifer recharge was identified. MAR may lead to changes in acid-base conditions (pH) and redox conditions (Eh) in aquifer environments. Such changes can then lead to changes in speciation of groundwater and solubilisation of some minerals from previously stable aquifers. Concerns were raised regarding the possibility of mobilising numerous chemicals including chromium, strontium, lead, iron, arsenic, fluoride and selenium. The need for improved techniques to assess the likelihood of chemical mobilisation was identified, as this would define the requirement for subsequent water treatment, residuals management and disposal. Conversely, it was noted that variable redox conditions may also prove to be advantageous in some cases where sequential aerobic and anoxic environments may lead to enhanced organic chemical contaminant degradation (analogous to the use of aerobic and anoxic zones in wastewater treatment). In circumstances where water is chlorinated prior to aquifer injection, residual chlorine and organic matter may lead to disinfection by-product formation within the aquifer. Depending on the characteristics of the aquifer, this may include an abundance of iodinated or brominated products, but little information is currently available to assess disinfection by-product formation during MAR. Hydraulic fracturing (or 'fraccing') processes used in coal seam gas extraction activities were identified as a specific form of MAR since they involve the high-pressure injection of aqueous fraccing solutions into coal seams. The need for improved knowledge and understanding of the implications of fraccing on aquifers was noted. Particular attention was focused on the wide variety of chemicals used in fraccing solutions and the need to identify which of those are most likely to lead to adverse impacts on groundwater quality. Some specific chemicals in fraccing solutions may also be identified for their use as potential indicators or surrogates for monitoring impacts of fraccing activities. Discussion regarding microbial contaminants led to an agreement that MAR can be an effective treatment process for a wide range of pathogens, but that validation methodology and opportunities for rapid monitoring were lacking. Furthermore, concern was expressed that MAR may lead to the introduction of new carbon sources and nutrients to aquifers, thus altering the microbial ecology. The possibility of opportunistic pathogens (such as mycobacteria) thriving in the altered conditions was identified as an unknown risk. Similar potential was identified for other species, such as amoeba, that may act as hosts for bacterial amplification under suitable conditions. Overall, enhanced methods for monitoring and assessing the performance of MAR processes for improving (and maintaining) water quality were identified as a current research need. As an important component of this, the use of existing techniques for assessing residence time and water age were recommended, such as stable isotope analyses. Finally, there was consensus regarding the importance of continually applying 'relative exposure assessment' in risk assessment activities. That is, when assessing the risks of exposure to contaminants from MAR activities, these exposures should be considered within the context of their significance compared to other sources of exposure to the same substances or species. Integration into Water Supply Systems and Implementation Issues The third group focussed on Integration into Water Supply Systems and Implementation Issues and was led by Mark O'Donohue. This group identified a number of Policy and Regulatory challenges to successful integration, including the need to clarify allocation issues, with concerns expressed about the adequacy of existing legislative frameworks to protect the water and recovery rights of project proponents once water is underground. -- Special Report Stuart Khan addressed the issue of Water Quality and Water Safety. Locations and types of Managed Aquifer Recharge schemes in Australia in 2011.
Water Journal May 2011
Water Journal August 2011