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MPCA guidance for setting wasteload allocations for regulated stormwater

Below is a summary of Minnesota Pollution Control Agency (MPCA) guidance for setting Wasteload Allocations (WLAs) for regulated stormwater.  This includes construction, Municipal Separate Storm Sewer Systems (MS4), industrial, and individually-permitted stormwater. Additional information can be found here under the [[Forms and guidance for TMDLs|guidance documents]] heading .

===Regulated construction stormwater===
*During development of a Total Maximum Daily Load (TMDL), data are generally not available to support identification of specific Best Management Practices (BMPs) for construction stormwater. It is therefore MPCA’s preference to utilize the Construction Stormwater General Permit to manage compliance with a TMDL. National Pollutant Discharge Elimination System (NPDES) permitted construction stormwater must be given a WLA for TMDLs where the pollutant/stressor is total suspended solids (TSS) (turbidity), phosphorus (excess nutrients or eutrophication), dissolved oxygen, or biota (plant, fish, or macroinvertebrate).  Construction stormwater should be given a single categorical WLA (i.e. one WLA for construction stormwater). However, it is acceptable to include construction stormwater as part of an overall categorical WLA for stormwater when the entire watershed load is from regulated stormwater discharges. The WLA for construction stormwater will typically range from 0.05 to 0.15 percent of the overall TMDL, minus the Margin of Safety. TMDLs that do not prescribe BMPs for construction stormwater should contain the following language in the implementation section of the TMDL report: '''The WLA for stormwater discharges from sites where there are construction activities reflects the number of construction sites one or more acres expected to be active in the watershed at any one time, and the best management practices (BMPs) and other stormwater control measures that should be implemented at the sites to limit the discharge of pollutants of concern. The BMPs and other stormwater control measures that should be implemented at construction sites are defined in the State's NPDES/SDS General Stormwater Permit for Construction Activity (MNR100001). If a construction site owner/operator obtains coverage under the NPDES/State Disposal System (SDS) [Permit] General Stormwater Permit and properly selects, installs and maintains all BMPs required under the permit, including those related to impaired waters discharges and any applicable additional requirements found in Appendix A of the Construction General Permit, the stormwater discharges would be expected to be consistent with the WLA in this TMDL. It should be noted that all local construction stormwater requirements must also be met.'''

===Regulated industrial stormwater===
*During development of a TMDL, data are generally not available to support identification of specific BMPs for industrial stormwater. It is therefore MPCA’s preference to utilize the Industrial Stormwater Multi-sector General Permit to manage compliance with a TMDL. Industrial stormwater must receive a WLA if the pollutant of impairment is part of benchmark monitoring for any industry in the impaired watershed. Data resulting from benchmark monitoring of industrial stormwater discharges cannot be used to establish a separate WLA for industrial stormwater. When effluent limits are established for an industrial sector, that sector may be given a separate WLA consistent with those effluent limits. Industrial stormwater should be given a single categorical WLA (i.e. one WLA for industrial stormwater). However industrial stormwater may be part of an overall categorical WLA for stormwater when the entire watershed load is from regulated stormwater discharges. TMDLs that do not prescribe additional BMPs for industrial stormwater should contain the following language in the implementation section of the TMDL report: '''The WLA for stormwater discharges from sites where there is industrial activity reflects the number of sites in the watershed for which NPDES industrial stormwater permit coverage is required, and the BMPs and other stormwater control measures that should be implemented at the sites to limit the discharge of pollutants of concern. The BMPs and other stormwater control measures that should be implemented at the industrial sites are defined in the State's NPDES/SDS Industrial Stormwater Multi-Sector General Permit (MNR050000) or facility specific Individual Wastewater Permit (MN00XXXXX) or NPDES/SDS General Permit for Construction Sand & Gravel, Rock Quarrying and Hot Mix Asphalt Production facilities (MNG490000). If a facility owner/operator obtains stormwater coverage under the appropriate NPDES/SDS Permit and properly selects, installs and maintains all BMPs required under the permit, the stormwater discharges would be expected to be consistent with the WLA in this TMDL. It should be noted that all local stormwater management requirements must also be met.'''