AN EMPIRICAL-MODEL FOR INTERPOLATING C-CENTER-DOT-T VALUES FOR CHLORINE INACTIVATION OF GIARDIA-LAMBLIA

The 1986 Amendments to the US Safe Drinking Water Act (SDWAA) require the U.S. Environmental Protection Agency (EPA) to promulgate drinking water regulations that specify disinfection and/or treatment for surfa ce water supplies. These regulations taken together are called the Sur face Water Treatment Rule (SWTR), Unfiltered systems are required to d emonstrate that disinfection alone achieves the minimum performance re quirements through the attainment of minimum C . t values [the product of disinfectant concentration (mg/L) and disinfectant contact (min)], Equations have been developed to estimate C . t values based on anima l infectivity and excystation data. These C . t values are contained i n the Guidance Document for the SWTR at discrete Values for pH, temper ature, chlorine concentration and inactivation level. Both the equatio ns and the published values have proven inadequate for direct use in m ost operating situations. Generally, treatment systems operate at leve ls other than the specified levels, making use of the published values difficult. Therefore, a new set of equations were developed to assist drinking water utilities in applying the C . t concept.