Gross contamination

Procedure for responding to gross contamination

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. The pool should be completely drained and all exposed and accessible surfaces scrubbed with a strong bleach solution (one cup of bleach per 3 gallons of water). Be sure the effluent from draining the pool is discharged directly to a sanitary sewer system or other approved wastewater disposal system.
4. Refill the pool with water.
5. The concentration of free available chlorine should be raised to 5 mg/L and the pH adjusted to 7.5 or less. 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.
6. Pools with a sand filter should be backwashed, pools with diatomaceous earth (DE) filters should have the diatomaceous earth replaced, and a clean filter installed for pools served by cartridge filters. Clean and disinfect the cartridge filter in place when contamination occurred.
7. The pool recirculation pump and equipment should be operated for a contact time of 16 minutes with a pH of 7.5 or less and a free available chlorine concentration of 5 mg/L or more to obtain a CT inactivation value of at least 80. Other contact times and free available chlorine concentrations required to obtain a CT of 80 are given in Table 1. CT refers to concentration (C) of free available chlorine in mg/L or ppm multiplied by the contact time (T) in minutes.
8. 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
   7. 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.
9. 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.