R18-5-114. Grades of Wastewater Treatment Plants and Collection Systems

The Department shall grade a wastewater treatment plant or collection system according to population equivalent served, degree of hazard to public health, class of facility, and degree of treatment, as follows: 1. Grade 1 includes: a. A stabilization pond that serves 2,000 or fewer persons; b. A wastewater treatment plant not designated as Grade 2, 3, or 4; or c. A collection system that serves 2,500 or fewer persons. 2. Grade 2 includes: a. A stabilization pond that is designed to serve more than 2,000 persons; b. An aerated lagoon; c. A facility that employs biological treatment based upon the activated sludge principle or trickling filters and is designed to serve 5,000 or fewer persons, except as provided in subsection (3)(c); or d. A collection system that serves between 2,501 to 10,000 persons. 3. Grade 3 includes: a. A facility that employs biological treatment based upon the activated sludge principle and is designed to serve 5,001 to 20,000 persons; b. A facility that employs trickling filtration and is designed to serve 5,001 to 25,000 persons; c. A variation of biological treatment based on the activated sludge principle that requires specialized knowledge, including contact stabilization, and is designed to serve 20,000 or fewer persons; or d. A collection system that serves 10,001 to 25,000 persons. 4. Grade 4 includes: a. A facility that employs biological treatment based upon the activated sludge principle and is designed to serve more than 20,000 persons; b. A facility that employs trickling filtration and is designed to serve a population equivalent more than 25,000 persons; or c. A collection system that serves more than 25,000 persons.