Full Description

The United States Environmental Protection Agency (USEPA) Surface Water TreatmentRule (SWTR), as adopted by California, requires all public water systems that use asurface water source to provide multibarrier treatment that achieves a total of 99.9percent reduction of Giardia cysts and 99.99 percent reduction of viruses through acombination of filtration and disinfection. In lieu of Maximum Contaminant Levels(MCLs) for Giardia and viruses, filter performance standards, based on turbidity, havebeen associated with pathogen removal credit. For standard media filters (defined asconventional, direct, diatomaceous earth, and slow sand by the USEPA) meeting aturbidity performance standard is sufficient to achieve specific log removal credit. Underthe federal SWTR filtration technologies, a technology not falling into one of these categories isconsidered an alternative filtration technology whose performance standards must beestablished by the state. Because of differences in filtration technology, each acceptedalternative filtration technology has its own turbidity performance requirements based ondemonstration studies. Bag filters have been conditionally accepted and permitted inCalifornia. However, in some installations the filters are not meeting the turbidityperformance standards. Initial attempts, using particle counters, to evaluate bag filterperformance found that the instruments were not adequate to identify the reason behindthe performance standard excursions as there was little or no reduction in turbidity, withsignificantly little change in filtered water particle concentrations. It was hypothesizedthat submicron-sized particles were present which influenced the turbidity performancestandards. Consequently, a protocol was developed in an attempt to document theexistence 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 theprocess 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 thedetermination of submicron-sized particles. Initial observations have led the Departmentto believe that the presence of submicron particles may be more wide spread than justone or two locations. Data collected from several different source waters to dateindicates that submicron-sized particles are present at several existing bag filtrationinstallations and at other source water locations across the State creating a potentialchallenge to achieving compliance with current turbidity performance standardsdesigned to control Cryptosporidium. Includes tables, figures.

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Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 15File Size: 1 file , 300 KB