o Review treatment program.

o Institute immediate online disinfection² to help with control

o Retest the water in 3 – 7 days.

• Continue to retest at the same time interval until one sample retest result is < 20 CFU/mL. With receipt of result < 20 CFU/mL, resume routine maintenance program and plan.
• If retest is ≥ 20 CFU/mL but < 100 CFU/mL, repeat online disinfection² and retest until < 20 CFU/mL attained.
• If retest is ≥100 CFU/mL but < 1000 CFU/mL, further investigate the water treatment program and immediately perform online disinfection ². Retest and repeat attempts at control strategy until < 20 CFU/mL attained.

o If retest is ≥ 1000 CFU/mL, undertake control strategy as noted below.

o Review the treatment program and provide appropriate notifications per section 4-1.6 of this Subpart.

o Institute immediate online decontamination³ to help with control

o Retest the water in 3 – 7 days.

• Continue to retest at the same time interval until one sample retest result is < 20 CFU/mL. With receipt of result < 20 CFU/mL, resume routine maintenance program and plan.
• If any retest is ≥ 20 CFU/mL but < 100 CFU/mL, repeat online disinfection² and retest until < 20 CFU/mL attained.
• If any retest is ≥ 100 CFU/mL but < 1000 CFU/mL, further investigate the water treatment program and immediately perform online disinfection.² Re-test and repeat attempts at control strategy until < 20 CFU/mL attained.
• If any retest is ≥ 1000 CFU/mL:
  •  carry out system decontamination⁴.

² Online disinfection means – Dose the cooling tower water system with either a different biocide or a similar biocide at an increased concentration than currently used.

³ Online decontamination means – Dose the recirculation water with a halogen-based compound (chlorine or bromine) equivalent to at least 5 milligrams per liter (mg/L) or parts per million (ppm) free residual halogen for at least one hour.

⁴ System decontamination means – Maintain between 5 to 10 mg/L (ppm) free residual halogen for a minimum of one hour; drain and flush with disinfected water; clean wetted surface; refill and dose to 1 – 5 mg/L (ppm) of free residual halogen and circulate for 30 minutes. Refill, re-establish treatment and retest for verification of treatment.

For chlorine treatment the pH range should be 7.0 to 7.6; for bromine treatment the pH range should be 7.0 to 8.7. At higher pH values the treatment times may need to be extended.

NOTE: Stabilized halogen products should not be used for online decontamination or system decontamination as defined in this Appendix per footnotes 3 and 4.