Summary of suggested stormwater criteria for MN receiving waters Summary of suggested stormwater criteria for MN receiving waters

Summary of suggested stormwater criteria for MN receiving waters
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Group Name	Suggested Stormwater Sizing Criteria1
Most-Sensitive Lakes	Recharge (Vre): HIGHLY RECOMMENDED if lake is fully or partially ground water dependent Water Quality (Vwq): Site-Based Phosphorus Load Reduction: To apply this HIGHLY RECOMMENDED criteria for the most sensitive lakes, a manager would compute pre- and post-development phosphorus load at the development site using Simple Method, P8, SLAMM or an equivalent water quality model. A TP load reduction is then calculated for the site based on a range of no change to a 25% reduction in post-development load, if additional load reduction is warranted. Designers document load reduction achieved using a list of BMP removal efficiencies. If on-site compliance is not possible, an offset fee can be charged which is equivalent to cost of removing similar mass of phosphorus elsewhere in the watershed. The offset may be applied at time of permit application in the form of bond held by the issuing agency Channel Protection (Vcp): HIGHLY RECOMMENDED if site drains to tributary stream to a lake
Sensitive Lakes	Recharge (Vre): HIGHLY RECOMMENDED if lake is fully or partially ground water dependent Water Quality (Vwq): Increased Water Quality Sizing: RECOMMEND MPCA pond rule 2 or 4 for “special waters”, depending on the BMP used. For sites with more than 30% Site IC, the Walker Rule (Section IX) presents another option that will result in similar TP removal Shorter BMP List: Only BMP designs or combination with a TP removal capability exceeding 50% should be used Channel Protection (Vcp): RECOMMENDED if site drains to tributary stream to a lake
Trout Streams	Recharge (Vre): RECOMMENDED in certain situations Water Quality (Vwq): RECOMMEND apply MPCA Sizing Rules 2 and 4, depending on BMP used. Comply with SWPPP requirement in CGP, as well as prohibited industrial discharges into infiltration systems. No infiltration of stormwater without pre-treatment. If site is designated as a potential stormwater hotspot, no infiltration of runoff should be allowed. Special precautions are advised for karst areas.
Surface Water Drinking Supplies	Recharge (Vre): RECOMMENDED for watersheds, with caution for ground water functioning as a surface water source Water Quality (Vwq): RECOMMEND apply the same sizing criteria as Sensitive Lakes Comply with SWPPP requirement in CGP
Susceptible Wetlands	Maintain Wetland Hydroperiods: For wetlands identified as HIGHLY or moderately susceptible in Table 10.12, meet the storm bounce and inundation duration limits set forth in Table 10.13. This may be done through infiltration, extended detention, or diversion Recharge (Vre): HIGHLY RECOMMENDED Water Quality (Vwq): RECOMMEND site-based phosphorus load reduction as described for Most Sensitive Lakes to control nutrients. Channel Protection (Vcp): RECOMMENDED if channel is direct tributary to the wetland No use of natural wetlands for stormwater treatment (REQUIRED) No constrictions at wetland outlets (RECOMMENDED)
Non-Susceptible Wetlands	Recharge (Vre): RECOMMENDED Water Quality (Vwq): No untreated stormwater discharges to wetlands (REQUIRED) which is operationally defined as providing Vwq via MPCA Rules 1 and 3 Channel Protection (Vcp): RECOMMENDED only if channel is direct tributary to the wetland
Impaired Waters for Computable Pollutants	Water Quality (Vwq): If new development site is located in a watershed subject to a TMDL that has no remaining stormwater allocation, designer may need to document no net increase in pollutant load; RECOMMEND using the general method proposed for the Most Sensitive Lakes but using the appropriate pollutant. Currently, sufficient data are only available to perform this calculation for sediment, phosphorus, nitrogen, ammonia, and bacteria Channel Protection (Vcp): RECOMMENDED when water body impaired for sediment or sediment related pollutant
Impaired Waters for Non-Computable Pollutants	Water Quality (Vwq): For the remaining ten pollutants which may be subject to a TMDL but have no remaining stormwater allocation, designers should satisfy appropriate MPCA sizing rules. Channel Protection (Vcp): RECOMMENDED when water body impaired for sediment related pollutant

¹REQUIRED- CGP requirement
HIGHLY RECOMMENDED- Essential to provide adequate management and good engineering
RECOMMENDED- Suggested for good management and engineering