Code
Formed-stool contaminated water shall have the FREE CHLORINE RESIDUAL checked and the FREE CHLORINE RESIDUAL raised to 2.0 mg/L (if less than 2.0 mg/L) and maintained for at least 25 minutes (or an equivalent time and concentration to reach the CT VALUE) before reopening the AQUATIC VENUE.
Annex
For formed-stool contamination, a free CHLORINE value of 2 mg/L was selected to keep the POOL closure time to approximately 30 minutes. Other CHLORINE concentrations or closure times can be used as long as the CT inactivation value is kept constant. The CT VALUE is the concentration (C) of FREE AVAILABLE CHLORINE in mg/L multiplied by time (T) in minutes: (CT Value = C x T).
For formed-stool contaminated water the CT VALUE for Giardia (45) is used as a basis for calculations:
Table 6.5.3.1: Giardia Inactivation time for Formed-Stool Contamination
Chlorine Levels (mg/L)
Disinfection Time*
1.0
45 minutes
2.0
25 minutes
3.0
19 minutes
*These closure times are based on a 99.9% inactivation of Giardia cysts by chlorine, pH 7.5, 77°F (25°C). The closure times were derived from the Environmental Protection Agency (EPA) Disinfection Profiling and Benchmarking Guidance Manual. They do not take into account “dead spots” and other areas of poor pool water mixing.