Limited contamination

Procedure for responding to limited contamination involving formed stool (solid, nonliquid), vomit, or blood

1. The pool is to be closed immediately, everyone directed to leave the pool enclosure, and all access doors or gates to the pool enclosure are to be locked. If there is another pool within the enclosure that clearly has not been contaminated, the enclosure may remain open and use of the non-contaminated pool allowed provided warning signs are posted around the contaminated pool and personnel are available to ensure that the contaminated pool is not used. Do not allow anyone to enter the contaminated pool until all decontamination procedures are completed.
2. All solid contaminants should be removed from the pool using a net or scoop and disposed of in a sanitary manner. Clean and disinfect the net or scoop. Vacuuming the pool to remove the contaminant is not recommended. 
3. Raise the free available chlorine concentration to 2 mg/L if it is less than 2.0 mg/L, and adjust the pH within a range of 7.2 to 7.5. Ensure this concentration is found throughout the pool by sampling at least three widely spaced locations away from return water outlets. This free available chlorine concentration was selected to keep the pool closure time to approximately 40 minutes. Other concentrations or closure times can be used as long as the CT inactivation value is maintained at 80 as shown in Table 1.
4. Maintain the free available chlorine concentration at 2.0 mg/L, pH in the range of 7.2 to 7.5, for at least 40 minutes before re-opening the pool. The free available chlorine levels in the presence of chlorine stabilizers such as chlorinated isocyanurates should be maintained at 4.0 mg/L. Ensure that the filtration system is operating while the pool reaches and maintains the proper free available chlorine concentration during the disinfection process. The impact of chlorine stabilizers (e.g., chlorinated isocyanurates such as tri-chlor and di-chlor) on pathogen inactivation and disinfectant measurement is unclear and requires further investigation. Michigan standards on chlorinated isocyanurates indicate the free available chlorine concentration needs to be doubled in their presence to accomplish an equivalent disinfection.
5. Document the incident on the monthly operation report or a separate log sheet by recording:
   1. date and time of the event,
   2. type and amount of contaminant,
   3. free available chlorine concentration and pH when the contamination was first noted,
   4. free available chlorine concentration and pH at the beginning and end of the contact time,
   5. free available chlorine concentration and pH when the pool is ready to be re-opened,
   6. the procedures followed to respond to the incident (including the process used to increase free chlorine residual if necessary), and the contact time. 
   Report the incident to the local health department and be sure to include these details in the discussions. If a contingency plan has not been prepared, obtain approval to re-open the pool from the local health department or the Department of Environment, Great Lakes, and Energy, Drinking Water and Environmental Health Division, Environmental Health Programs Unit.
6. The pool may be re-opened and swimmers may be allowed into the pool after the required CT value has been achieved, the free available chlorine level has been returned to the normal operating range of 1 to 5 mg/L, and the pH is adjusted to the normal operating range of 7.2 to 7.5. If necessary, consult the local health department, Department of Environment, Great Lakes, and Energy, or an aquatics professional for recommendations on bringing the free available chlorine levels back to an acceptable operating range. 

Procedure for responding to limited contamination from diarrhea (liquid stool)

1. The pool is to be closed immediately, everyone directed to leave the pool enclosure, and all access doors or gates to the pool enclosure are to be locked. If there is another pool within the enclosure that clearly has not been contaminated, the enclosure may remain open and use of the non-contaminated pool allowed provided warning signs are posted around the contaminated pool and personnel are available to ensure that the contaminated pool is not used. Do not allow anyone to enter the contaminated pool until all decontamination procedures are completed.
2. All solid contaminants should be removed from the pool using a net or scoop and disposed of in a sanitary manner. Clean and disinfect the net or scoop. Vacuuming the pool to remove the contaminant is not recommended.
3. Raise the free available chlorine concentration to 20 mg/L and maintain the pH between 7.2 and 7.5. Ensure this concentration is found throughout the pool by sampling at least three widely spaced locations away from return water outlets. The concentration of chlorine and the pH must be determined using a properly maintained and approved test kit, and the readings of automatic sensing equipment should not be used. The chlorine and pH level should be sufficient to inactivate Cryptosporidium and should be maintained for at least 12 hours, equivalent to a CT inactivation value of 14,400. A higher or lower free available chlorine level/inactivation time can be used as long as a CT inactivation value equaling 14,400 is maintained for Cryptosporidium inactivation. Table 2 provides other times and free available chlorine concentrations correlating to a CT value of 14,4005. 
4. Ensure that the filtration system is operating while the pool reaches and maintains the proper free available chlorine concentration during disinfection.
5. Backwash the filter thoroughly after reaching the CT value. Be sure the effluent is discharged directly to waste and into a sanitary sewer or other approved wastewater disposal system. Do not return the backwash through the filter. Where appropriate, replace the filter media. 
6. After the CT value has been reached, adjust the free available chlorine level to the normal operating range of 2 to 5 mg/L and adjust the pH to a level of 7.2 to 7.5. If necessary, consult an aquatics professional, a local health department representative, or a representative of the Environmental Health Programs Unit, Drinking Water and Environmental Health Division, Department of Environment, Great Lakes, and Energy for recommendations on bringing the free available chlorine levels back to an acceptable operating range. 
7. Document the incident on the monthly operation report or a separate log sheet by recording:
   1. date and time of the event,
   2. type and amount of contaminant,
   3. free available chlorine concentration and pH when the contamination was first noted,
   4. free available chlorine concentration and pH at the beginning and end of the contact time,
   5. free available chlorine concentration and pH when the pool is ready to be re-opened,
   6. the procedures followed to respond to the incident (including the process used to increase free chlorine residual if necessary), and the contact time. 
   Report the incident to the local health department and be sure to include these details in the discussions. If a contingency plan has not been prepared, obtain approval to re-open the pool from the local health department or the Department of Environment, Great Lakes, and Energy, Drinking Water and Environmental Health Division, Environmental Health Programs Unit.
8. The pool may be re-opened and swimmers may be allowed into the pool after the required CT value has been achieved, the free available chlorine level has been returned to the normal operating range of 1 to 5 mg/L, and the pH is adjusted to the normal operating range of 7.2 to 7.5. If necessary, consult the local health department, Department of Environment, Great Lakes, and Energy, or an aquatics professional for recommendations on bringing the free available chlorine levels back to an acceptable operating range. 

Table 1 - Free available chlorine concentrations and contact time required to obtain a CT inactivation value of 80

This table applies to disinfection of pools after a formed fecal incident or after gross contamination.

Table 2 -Pool closure times and disinfectant concentrations necessary to obtain a CT inactivation value of 14,400

This table is to be used for pools following a limited contamination event from diarrhea.