AWWA JAW60864

Riverbank filtration (RBF) has been recommended as a treatment process to remove Cryptosporidium parvum in surface waters. A comprehensive study was undertaken in southwestern Ohio to investigate several aspects of RBF, specifically the effects of infiltration, streambed scour, and high river-stage frequencies on RBF efficiency and potential breakthrough of pathogens. During periods of high river stage and flow, scour of the streambed (e.g., removal of the fine-grained sediments on the bottom of a river) may occur. Scour has been thought to reduce the filtration capability of an RBF system, and the US Environmental Protection Agency has held that scour of the streambed at RBF sites is problematic. In other words, if the streambed is removed, the system becomes vulnerable to breakthrough by Cryptosporidium and other pathogenic protozoa. This study, undertaken in part to investigate this concern, found no direct evidence that scour occurred at any degree of magnitude at this site or had any adverse effect on water quality. In addition, this work examined variations in the rate of infiltration of surface water caused by high river-stage events and found that the frequency of occurrence for high-infiltration periods was low. Results indicated that the streambed and aquifer were able to buffer water quality effects from major increases in the infiltration rate. Until now, these significant issues surrounding RBF had not been fully investigated and were only partially understood. This research should help build confidence in RBF as an important treatment tool that can help utilities comply with the Surface Water Treatment Rule and other regulations. Includes 21 references, figures.