Drinking Water 

CT Compliance Calculation Program

CT Compliance Software Available

The Engineering Section has developed a software application available to use for determining compliance with CT requirements of the Surface Water Treatment and Ground Water Rules as well as inactivation of Microcystin-LR.

The Engineering Section first developed a DOS software program developed in the 1990’s to calculate the required CT value or the percent of the required CT value achieved from 0.5 to 3.0-log Giardia cyst inactivation for all approved disinfectants. It also calculated the CT values from 2.0 to 4.0-log for virus inactivation using ozone, chlorine dioxide and chloramines. This program does not work well on newer versions of Windows and therefore is no longer available; however a newer application has been developed.

The current software program was first developed in 2009 for the purposes of including all CT values up to 3.0-log Giardia Cyst and 4.0-log Virus inactivation for all approved disinfectants as well as up to 4.0-log Cryptosporidium Oocyst for Ozone and Chlorine Dioxide. In 2016, it has been updated to include CT for the inactivation of Microcystin-LR for use in the response to potential Harmful Algal Blooms which may release cyanotoxins into the water supply. This application is more versatile than the original DOS program and allows for multiple segments of a treatment plant to be used in the calculations. This program is available in the form of an (Office 2003) Excel spreadsheet file ( CT-TableCalc.xls ) and requires use of Microsoft Excel or other program capable of running *.XLS files.

Both applications use interpolated CT table data as published in the Surface Water Treatment Rule and Guidance Manual and do not use an empirical formula to estimate CT values. The data obtained with the programs should match data from manually checking the CT tables.

CT-TableCalc V1.xls