Application of the Australian Guidelines for Water Recycling: Managing Health and Environmental Risks
The Australian Guidelines for Water Recycling – Managed Aquifer Recharge provide a ready-to -use and user-friendly compendium of knowledge. Practical instructions and checklists provide a step wise approach with a strong focus on implementation. The proposed models for water flow and substance transport allow a first tier estimation of present concentrations in ambient groundwater and the impacted zone in the aquifer. The use of stochastic models is not mandatory within the guidelines. A criticism which can be identified related to the use of models simply based on point estimates, is that especially in early stage risk assessments, where uncertainties are usually high, these models tend to pretend a level of certainty which often does not represent reality. Risks associated to inorganic chemicals are required to be treated with more detail. Rigorous quantification of biodegradation kinetics (e.g. first-order rate constants) and adsorption parameters (e.g. linear distribution coefficients) for EOCs during subsurface passage determined on field scale are still scarce. It is clear that first-order rate constants and linear distribution coefficients provide only a simplified description of the removal mechanisms during subsurface passage, because they neglect spatial and temporal dynamics of physical and chemical conditions. Nevertheless, this approach often provides a good approximation and allows also for site independent comparison of removal processes. Regarding the demonstration site in Berlin-Tegel the analysis showed that if the model of the Australian Guidelines is applied to the MAR system the travel time of 50d during subsurface passage cannot be guaranteed. In Germany, a residence time of 50d is usually considered to sufficiently reduce the risk of microbial hazards. Although risk calculations did not reveal immediate concern, it is recommended to develop and apply suitable verification monitoring techniques to quantify travel times and reduce present uncertainties. Moreover, this risk assessment and the study about the influence of the groundwater replenishment site on ambient groundwater (Sprenger and Grützmacher, 2015) clearly showed the need for protective measures against the input of undesired substances from shallow ambient groundwater.