AWWA JAW37657

The Surface Water Treatment Rule (SWTR) stipulates filtration and disinfection requirements for public water systems using surface water or groundwater under the direct influence of surface water. In Ohio, 169 treatment plant serving 5,000,000 people are affected by the SWTR. The authors surveyed these plants to determine how the SWTR's C x T requirements have affected system operation. Existing plants use a wide variety of clearwell configurations. Although tracer studies provide the most reliable estimates of clearwell contact time, few of these systems actually ran tracer tests; instead most accepted a conservative estimate of effective contact time developed by the Ohio Enviromental Protection Agency to roughly estimate effective contact time. Determining contact times in the absence of a tracer study presents a unique challenge to enforcement agencies because of the variety of chlorine contact chambers encountered in practice. Under a conservative worst-case scenario, more than half of Ohio's SWTR treatment plants were judged unable to comply with C x T requirements. Includes 7 references, tables, figures.