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Q14495 - INFO: CT Tables

Instructions for using tables (from EPA Guidance Manual Disinfection Profiling and Benchmarking)

1. Find the CT Table for the temperature that is equal to (or slightly below) the actual temperature of the water. For example, using Free Chlorine for the inactivation of Giardia Cysts if the temperature is 19°C, use the 15°C table (Table C-4).

2. Go to the section of the table for the pH which is equal to (or slightly above) the actual pH of the water. For example, if the pH is 7.2, use the pH=7.5 section.

3. Look at the far left side of the table and find the chlorine concentration that is equal to (or slightly above) the actual free chlorine concentration. For example, if the chlorine concentration is 1.1 mg/L, use the 1.2 mg/L row. If the chlorine concentration is above 3mg/L, use the values corresponding to 3mg/L.

4. The value shown at the intersection of the concentration row and the temperature/pH column is the value of the required CT3-log, Giardia. For example, at pH 7.5, 15°C, and 1.2 mg/L of chlorine, the required CT3-log, Giardia is 92 mg-min/L.

Example:  Use the CT Spread or CT Math Toolbox function:

CT(1, 1, 1.5, .4, 7.6, .82) = 152

InactivationOf = 1 is for Giardia
Disinfectant = 1 is for Free Chlorine
LogInactivation = 1.5
Free Cl2 Residual=.82

1. Use Table C-1 for Giardia by Free Chlorine for Temperature 0.5 C or lower (.4) 

2. Use Section pH=8 since 8 is slightly above our pH of 7.6.

3. Use Chlorine Concentration of 1 since 1 is above our Chlorine of .82.

4. The CT Required for 1.5 log inactivation is 152 mg-min/L.  The intersection of 1.5 and 1. 



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Created on 3/12/2018 8:38 PM.
Last Modified on 2/14/2019 3:13 PM.
Last Modified by Scott Dorner.
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