(1) Full time disinfection with chlorine, chlorine dioxide, chloramines, or a disinfectant that maintains a residual is mandatory where the source of water is from lakes, reservoirs, or streams, or ground water sources under the direct influence of surface water, or where the water may be exposed to a potential source of contamination including, but not limited to:

(a) losses of pressure within the system that could result in backflow or infiltration conditions; or

(b) substandard distribution, pumping or storage facilities.

(2) Full time disinfection of the water supply is mandatory whenever the water may be exposed to a potential source of contamination through:

(a) treatment processes, as determined by the department; or

(b) unprotected or poorly protected ground water sources.

(3) Full time disinfection of the water in a ground water supply system is mandatory whenever the record of bacteriological tests of the system does not indicate a safe water under the criteria listed in ARM 17.38.207 and 17.38.215. Full time disinfection with chlorine, chlorine dioxide, chloramines, or a disinfectant that maintains a residual may be required where the history and nature of the contaminant indicate a residual is required to ensure safe water.

(4) Methods of full time disinfection must be reviewed and approved by the department prior to the installation or use of any form of treatment.

(5) The residual disinfectant concentration measured as free chlorine, total chlorine, combined chlorine, chlorine dioxide, or other department approved disinfectant(s) , in the distribution system of a ground water supply system required by the department to use continuous disinfection with chlorine, chlorine dioxide, chloramines, or a disinfectant that maintains a residual must not be less than 0.2mg/l using the DPD method or 0.1mg/l using the amperometric titration method. A heterotrophic bacteria concentration in water in the distribution system less than or equal to 500 per milliliter, measured as heterotrophic plate count (HPC) , is an acceptable substitute for disinfectant residual for purposes of determining compliance with this rule.