AWWA WQTC62518

The United States Environmental Protection Agency (USEPA) Surface Water Treatment Rule (SWTR), as adopted by California, requires all public water systems that use a surface water source to provide multibarrier treatment that achieves a total of 99.9 percent reduction of Giardia cysts and 99.99 percent reduction of viruses through a combination of filtration and disinfection. In lieu of Maximum Contaminant Levels (MCLs) for Giardia and viruses, filter performance standards, based on turbidity, have been associated with pathogen removal credit. For standard media filters (defined as conventional, direct, diatomaceous earth, and slow sand by the USEPA) meeting a turbidity performance standard is sufficient to achieve specific log removal credit. Under the federal SWTR filtration technologies, a technology not falling into one of these categories is considered an alternative filtration technology whose performance standards must be established by the state. Because of differences in filtration technology, each accepted alternative filtration technology has its own turbidity performance requirements based on demonstration studies. Bag filters have been conditionally accepted and permitted in California. However, in some installations the filters are not meeting the turbidity performance standards. Initial attempts, using particle counters, to evaluate bag filter performance found that the instruments were not adequate to identify the reason behind the performance standard excursions as there was little or no reduction in turbidity, with significantly little change in filtered water particle concentrations. It was hypothesized that submicron-sized particles were present which influenced the turbidity performance standards. Consequently, a protocol was developed in an attempt to document the existence of particles that were smaller than the lowest channel in the particle counters (2 m). One of the key objectives of developing this test protocol was to keep the process simple enough to allow field staff and small system operators to perform the test in the field. The test has proven to be a simple and feasible method in the determination of submicron-sized particles. Initial observations have led the Department to believe that the presence of submicron particles may be more wide spread than just one or two locations. Data collected from several different source waters to date indicates that submicron-sized particles are present at several existing bag filtration installations and at other source water locations across the State creating a potential challenge to achieving compliance with current turbidity performance standards designed to control Cryptosporidium. Includes tables, figures.