Code
In AQUATIC VENUE water that contains cyanuric acid or a stabilized CHLORINE product, water shall be treated by:
1) Lowering the pH to 6.5, raising the FREE CHLORINE RESIDUAL to 40 mg/L using a non-stabilized CHLORINE product, and maintaining at 40 mg/L for at least 30 hours or an equivalent time and concentration needed to reach the CT VALUE. (Measurement of the inactivation time required shall start when the aquatic venue reaches the intended FREE chlorine level.) or;
2) Circulating the water through a SECONDARY DISINFECTION SYSTEM to theoretically reduce the number of Cryptosporidium OOCYSTS in the AQUATIC VENUE below one OOCYST/100 mL as outlined in MAHC Section 4.7.3.3.2.4 or;
3) Draining the AQUATIC VENUE completely.
Annex
CHLORINE stabilizers such as cyanuric acid slow DISINFECTION; therefore, higher CHLORINE levels may be necessary to reach the CT VALUE for Cryptosporidium inactivation in POOLS using CHLORINE stabilizers. Limited data suggest that a 3-log inactivation of Cryptosporidium is possible in more extreme conditions when 50 PPM cyanuric acid was present in the water (pH of 6.5, FREE CHLORINE RESIDUAL of 40 mg/L).501 The level of cyanurate mentioned above (i.e., 50 PPM) was the concentration used in the experiment and should not be construed with suggested operating conditions; POOL operators should not add additional cyanurate to a POOL to reach 50 PPM. Higher levels of stabilization (i.e., over 50 PPM) may or may not decrease DISINFECTION efficacy further so more data are needed to address the issue.
Along with the pH level and FREE CHLORINE RESIDUAL, the cyanuric acid level should be checked and adjusted if necessary prior to reopening the POOL.
Data are not currently available for remediation procedures with POOLS that contain stabilized CHLORINE or cyanuric acid. CDC has extrapolated current data and has the following suggestions for remediation.
In POOL water that contains CHLORINE stabilizer such as cyanuric acid under 50 mg/L, the pH should either be lowered to 6.5 and the FREE CHLORINE RESIDUAL shall be raised to 40 mg/L using a non-stabilized CHLORINE product and maintained for at least 30 hours or an equivalent time to reach the same CT VALUE as shown in the MAHC Annex 6.5.3.2. Further data are being collected by CDC to better address the issue of HYPERCHLORINATION of Cryptosporidium in POOLS using stabilizers in POOL water that contains CHLORINE stabilizer such as cyanuric acid under 50 mg/L.
Another method for remediation could be reached by dilution, draining the POOL of enough water to reach 50 mg/L stabilizer and then following the procedure above. If that cannot be accomplished, the POOL could be drained completely and scrubbed.
AQUATIC VENUES with SECONDARY DISINFECTION SYSTEMS could be closed and allowed to circulate for the length of time calculated in MAHC Section 4.7.3.3.2 to reduce the level of Cryptosporidium below one OOCYST/100mL