(1) All water supply systems and wastewater systems are classified according to population served and type of treatment as shown below:

(a) Water distribution systems:

(i) Class 1--serving more than 20,000 people;

(ii) Class 2--serving 2,500 to 20,000 people;

(iii) Class 3--serving 500 to 2,500 people;

(iv) Class 4--serving 100 to 500 people;

(v) Class 5--serving fewer than 100 people.

(b) Water treatment systems:

(i) Class 1--treatment for surface water utilizing chemical coagulation, filtration, and disinfection;

(ii) Class 2--treatment for surface water not utilizing chemical coagulation;

(iii) Class 3--well water supply serving greater than 2,500 people, with or without disinfection;

(iv) Class 4--well water supply serving 100 to 2,500 people, with or without disinfection;

(v) Class 5--well water supply serving fewer than 100 people, with or without disinfection.

(c) Wastewater treatment systems:

(i) Class 1--conventional, high rate, or biological nutrient removal activated sludge systems or any treatment system with mechanical tertiary (advanced) treatment processes;

(ii) Class 2--treatment such as extended aeration, oxidation ditches, trickling filters, package plants, sequencing batch reactors, or bio-disc treatment systems;

(iii) Class 3--aerated lagoons;

(iv) Class 4--lagoons not utilizing artificial aeration.

(d) Industrial wastewater treatment systems:

(i) Class 1--physical-chemical treatment facilities for precipitation and settling and/or biological treatment plants treating more than 1.0 mgd;

(ii) Class 2--biological treatment plants treating less than 1.0 mgd;

(iii) Class 3--treatment facilities primarily for oil removal;

(iv) Class 4--ponding facilities for removal of sediment which do not utilize chemical treatment.

(2) In order to calculate the class of a particular water supply system pursuant to (1) (a) or (b) when an accurate population census is not available, the population served may be determined by multiplying the number of service connections by 2.5.

(3) For the purposes of this subchapter, a system classified with a lower number is considered more complex than a system classified with a higher number, i.e., a Class 1 system is more complex than a Class 2 system.