N.Y. Comp. Codes R. & Regs. tit. 10, APPENDICES, app 4-A
(cf. Part 4)
Interpretation of Legionella Culture Results from Cooling Towers
Legionella Test Results in CFU/mL1 | Response |
No detection (<20 CFU/mL) | Maintain treatment program and Legionella monitoring in accordance with the maintenance program and plan. |
For levels at >=20 CFU/mL but <1000 CFU/mL perform the following: | * Review treatment program. * Institute immediate online disinfection2 to help with control. * 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. * If retest is > 1000 CFU/mL, undertake control strategy as noted below. |
For levels >1000 CFU/mL perform the following: | * Review the treatment program and provide appropriate notifications per section 4-1.6 of this Subpart. * Institute immediate online decontamination3 to help with control. * 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 |
1 Colony forming units per milliliter.
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.
N.Y. Comp. Codes R. & Regs. tit. 10, APPENDICES, app 4-A
Stabilized halogen products should not be used for online decontamination or system decontamination as defined in this Appendix per footnotes 3 and 4.