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Permeable Pavement and Pavers as Pervious Surface <br />5/29/2024 <br />Page 2 <br />VOLUME REDUCTION CREDIT SCHEDULE <br />Hydrologic <br />Soil Group <br />Design <br />Guidance <br />Volume <br />Control (VC) <br />Credit <br />Calculation <br />Methods <br />HSG A <br />Minnesota <br />Stormwater <br />Manual <br />1-inch credit <br />over the surface <br />area <br />VC = 1/3 x area of <br />permeable surface <br />HSG B <br />Minnesota <br />Stormwater <br />Manual <br />1-inch credit <br />over the surface <br />area <br />VC = 1/4 x area of <br />permeable surface <br />HSG C &D <br />Minnesota <br />Stormwater <br />Manual <br />1-inch credit <br />over the surface <br />area <br />VC = 1/6 x area of <br />permeable surface <br />2.To determine the hydrologic soil group, designers shall test the in-situ soil infiltration rate by <br />two soil pit measurements completed with a double-ring infiltrometer. <br />3.Permeable pavement and pavers shall be designed in accordance with the Minnesota <br />Stormwater Manual. <br />4.For hydrologic soils groups C or D, a 4-to-6-inch diameter perforated PVC (AASHTO M-252) <br />schedule 40 pipe (underdrain) shall be installed for the full length of the permeable pavement <br />cell, and non-perforated pipe, as needed, connected to storm drainage system. <br />5.Over time permeable pavement and pavers become less effective and act more like traditional <br />impervious surfaces. A stormwater management facility must be designed for maintenance <br />access and maintained in perpetuity to function as designed. <br />6.As a condition of permit issuance, a permittee must sign and record on the title a stormwater <br />facility maintenance agreement, in a form supplied by the City or otherwise acceptable to it, <br />that provides for perpetual facility maintenance. <br />7.Permeable pavement and pavers surfaces should be discouraged in areas of commercial or <br />multi-family traffic. <br />8.Permeable pavement and pavers surfaces should be discouraged where salt exposure is likely <br />to occur unless pavers have been sealed with an epoxy or sealant. <br />9.Permeable pavement and pavers surfaces are highly susceptible to clogging from high <br />sediment loading runoff areas such as gravel parking lots, routinely disturbed or bare ground <br />areas, or wooded areas with light ground cover. Pervious pavers should be located away from <br />these source runoff areas. <br />10.Permeable pavement and pavers that will infiltrate water into the subgrade soil should be <br />located a sufficient distance from downgradient steep slopes to minimize the potential for slope <br />failures or erosion due to seepage. <br />References: <br />AS Braswell, RJ Winston, WF Hunt, 2018, Hydrologic and water quality performance of <br />permeable pavement with internal water storage over a clay soil in Durham, North Carolina, <br />Journal of Environmental Management 224, 277-287 <br />US EPA, 2021, NPDES: Stormwater Best Management Practice—Permeable Pavements <br />Minnesota Pollution Control Agency, 2024, Minnesota Stormwater Manual