Each nonresidential user's wastewater treatment cost contributions as determined in Section 13.28.030 and 13.28.040 shall be added together to determine such user's annual wastewater service charge. Residential users shall be considered to be one (1) class of user and an equitable service charge shall be determined for each user based on an estimate of the total wastewater contribution of this class of user. Vernal City may classify industrial, commercial and other nonresidential establishments as a residential user; provided, that the wastes from these establishments are equivalent to the wastes from the average residential user with respect to volume, suspended solids and BOD. (Ord. 80-8 § 4)