AWWA WQTC57183

As part of the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), the US Environmental Protection Agency (USEPA) is in the process of developing a "CT" table for the inactivation of Cryptosporidium with ozone at drinking water treatment plants. This paper discusses the approach commonly used by the USEPA in the development of a CT table which includes two primary steps. The first is data modeling, which includes fitting available data with a microbial inactivation model to determine the value of the model parameter(s). The second step includes the use of statistical analysis to develop an uncertainty factor that would then be applied to CT values calculated by the model. The need for a safety factor is driven primarily by the observation that significant scatter in the inactivation results exists. Includes 5 references, table, figures.