The purpose of the CT Helper (PDF) is to assist public water supply system operators in developing a working knowledge of how to determine CT credit, log inactivation and total log removal and/or inactivation. An example calculation is provided along with a blank CT calculation worksheet. In addition, the log inactivation determined by completing the CT calculation worksheet can be utilized in the development of the disinfection profile and the determination of the benchmark for the disinfection practice employed by the treatment facility.
Public water supply systems classified as being groundwater may also utilize the CT Helper to assist them with obtaining 4-log treatment of viruses certification under the Groundwater Rule (GWR). A simplified calculation spreadsheet entitled Understanding CT is available to groundwater systems to assist them with documenting 4-log treatment of viruses capability where their disinfection contactor consists of a non-branching length of waterline. Groundwater systems that practice disinfection in a groundwater treatment plant may utilize a more comprehensive tool called the The Groundwater Rule (GWR) Contact Time (CT) Calculator, a simplified spreadsheet developed by the U.S. Environmental Protection Agency (USEPA) for use by groundwater systems that disinfect in water treatment plants. EPA's spreadsheet can be found in the "Guidance on the Ground Water Rule" portion of their Water: Ground Water Rule webpage.
Please email Dan Clair, Chief, Engineering and Permits Unit, or call at 785-296-5516 for assistance with CT calculations or for either of the referenced CT calculation spreadsheets for 4-log treatment of viruses certification.