New York Codes, Rules and Regulations
Title 10 - DEPARTMENT OF HEALTH
Chapter - APPENDICES
Appendix 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.
Stabilized halogen products should not be used for online decontamination or system decontamination as defined in this Appendix per footnotes 3 and 4.
