Water Quality Improvements through the Environmental Buffer in Indirect Potable Reuse – Perception and Reality

With dwindling freshwater supplies worldwide, drinking water augmentation with reclaimed water has received increasing interest in many parts of the world. The use of reclaimed water for drinking water supplies historically was been divided into two categories: indirect potable reuse (IPR) and direct potable reuse. Both employ a sequence of treatment processes after conventional wastewater treatment. However, IPR projects were distinguished from direct potable reuse projects by the presence of an environmental buffer between the wastewater effluent and the potable water supply. An environmental buffer is defined as a water body or aquifer, perceived by the public as natural, which serves to sever the connection between the water and its history. The buffer also may: (a) provide an opportunity to blend or dilute the reclaimed water; (b) increase the amount of time between when the reclaimed water is produced and it is introduced into the water supply; and, (c) decrease the concentration of contaminants through various attenuation processes. While the latter three functions of environmental buffers (i.e., a-c) have potentially important implications for public health, performance standards for buffers were never defined. Rather, it was the perception that the water passed through a natural system and its role in increasing public acceptance of the subsequent use of the water in potable supplies that led to the perception that environmental buffers usually had to be included in potable water reuse projects. In many indirect potable reuse applications, natural treatment processes such as soilaquifer treatment (SAT) or riverbank filtration (RBF) are increasingly recognized as a key barrier for contaminants of concern. Natural treatment processes can dampen source water quality variations; attenuate pathogens as well as inorganic (such as nitrogen and phosphorus) and organic constituents (such as DBP precursors and regulated and unregulated chemicals occurring at the nanogram-per-liter level); and provide storage and blending with native groundwater. Although natural processes such as SAT and RBF are widely used, some key boundary conditions for attenuation of these water constituents to occur are still not identified.This study explored perceived and true benefits of various environmental buffers in IPR systems, but also examined reservoir/stream augmentation and different managed groundwater recharge systems operated under a wide range of conditions to identify the key boundary conditions that result in optimal performance of these systems. The study also highlighted the limitations of these natural treatment systems. This study was conducted using laboratory-scale column experiments and monitoring campaigns at fullscale groundwater recharge facilities across the United States.