(a) A wastewater treatment facility must be designed with a flow equalization basin if:(1) the total daily influent flow volume or total daily influent organic loading occurs during a period less than or equal to ten hours; or(2) the wastewater treatment facility receives an influent flow of less than 10% of its design flow or an influent organic loading less than 10% of its design organic loading during a period of time equal to or greater than 48 hours in any period of seven consecutive days.(b) A flow equalization basin must have an upstream screening device or grinding device.(c) A flow equalization basin must include an aeration system sized to maintain a dissolved oxygen level of at least 1.0 milligram per liter (mg/l) throughout the flow equalization basin.(d) A flow equalization basin must include a mixing system sufficient to prevent solids from settling.(e) The size of a flow equalization basin must be based on diurnal flow variations and the size and capacity of downstream process units. The engineering report must include the calculations justifying the size of a flow equalization basin.(f) For pumped flow to an equalization basin, the effluent from the basin must be controlled by a flow-regulating device capable of maintaining a flow rate that allows downstream process units to operate as designed.(g) For pumped flow from an equalization basin, a variable-speed pump or multiple pumps are required to deliver a constant flow to downstream treatment units.