Section 352.600  Mass Loading Limits

Whenever a water quality based effluent limitation (WQBEL) is established in a permit, the WQBEL shall be expressed as both a concentration value and a corresponding mass loading rate.

a)         Both mass and concentration limits shall be based on the same permit averaging periods such as daily or monthly averages, or in other appropriate permit averaging periods.

b)         The mass based WQBEL shall be calculated using effluent flow rates that are the same as those used in establishing the concentration-based WQBEL.

c)         Mass load limits are not required for parameters which cannot be appropriately expressed in terms of mass as listed below:

            pH

            temperature

            radiation

            bacteria

            dissolved oxygen

d)         Discharges that are subject to substantial flow variation  such as wet weather flows or varied production schedules may have mass limits established in a tiered fashion coinciding with different flow regimes. Typically two tiered mass limits will be established. One set shall be based on dry-weather effluent flowrate and the appropriate stream design flow. The second mass limit shall be based on effluent and stream flowrates representative of wet weather conditions.