- 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.
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.