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This document provides guidance on what loads are appropriate for inclusion in a Total Maximum Daily Load (TMDL) Wasteload Allocation (WLA) for regulated stormwater and summarizes the guidance document on what discharges should be included in the TMDL wasteload allocation for MS4 stormwater.
Summary of guidance
- The WLA must include all discharges from a regulated stormwater conveyance system (Municipal Separate Storm Sewer System or MS4).
- The WLA must include all current discharges comprised of drainage fromwithin a regulated municipality or township and that are to a regulated conveyance.
- The WLA for a regulated MS4 owned or operated by a county, watershed district, road authority, or other non-traditional (e.g. state college or university, state hospital, etc.) entity should only include the area of their MS4 system. Additional discharges, current or future, would only be included for property owner or operated by that entity.
- Current or future discharges comprised of drainage from outside a regulated municipality or township must be included in the Load Allocation (LA).
- A separate Reserve Capacity cannot be developed for regulated stormwater. Future discharges may be included in the WLA or the LA.
- Future discharges from MS4s that are currently permitted can be determined using land use plans or similar documents.
- Non-regulated MS4s that will be under National Pollutant Discharge Elimination System (NPDES) permit coverage in the future may be accounted for in the WLA. These MS4s should receive individual WLAs.
- Load may be transferred from either the LA or WLA to a WLA. The TMDL should clearly define the process for transferring load in the case that such transfers are needed to account for growth or because of changes to a MS4.
- Direct discharges from nonpoint sources to an impaired water cannot be regulated under a NPDES permit. However, for purposes of practicality, loads associated with these discharges may be placed into the WLA if they are not easily quantifiable and constitute a small percentage of the total WLA.
- The WLA for stormwater may include discharges from municipal, construction, and industrial stormwater if all industrial and construction stormwater discharges occur within the current or future boundaries of a regulated municipality or township.
The flow chart below can be used to determine if a specific load should be placed into the LA or the WLA.
For more information contact the Minnesota Pollution Control Agency at 651-296-6300 or 800-657-3864.