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additional precipitation durations to determine the critical duration flood event. Analysis of the 10 -day snowmelt event is not required for stormwater management detention basins with a defined outlet elevation at or below the 100 -year 24-hour event elevation. 4) Water quality treatment. a. Land development activities creating impervious surface shall address the use of better site design (BSD) techniques as outlined in the Better Site Design and Low Impact Development sections of the Minnesota Stormwater Manual (MPCA, 2014 and subsequent revisions). b. The water quality volume standard for all projects, except Public Linear projects, is determined as follows (Table 2): Table 2. Required Water Quality Volume Calculations for New or Reconstructed Deve ouments BMP BMP Design Variation Water Quality Treatment Volume Calculation [ft3J Infiltration Infiltration Feature Impervious surface [ft2] * 1.1 [in] / 12 [in/ft] Water Reuse Irrigation Impervious surface [ft2] * 1.1 [in] / 12 [in/ft] Biofiltration Underdrain Impervious surface [ft2] * 1.1 [in] / (0.65 * 12 [in/ft]) Filtration Sand or Rock Filter Impervious surface [ft2] * 1.1 [in] / (0.50 * 12 [in/ft]) Stormwater Wetlands Shallow Wetland Impervious surface [ft2] * 1.1 [in] / (0.40 * 12 [in/ft]) Pond/Wetland Impervious surface [ft2] * 1.1 [in] / (0.55 * 12 [in/ft]) Stormwater Ponds Wet Pond Impervious surface [ft2] * 1.1 [in] / (0.50 * 12 [in/ft]) Multiple Pond Impervious surface [ft2] * 1.1 [in] / (0.60 * 12 [in/ft]) c. The required water quality treatment volume standard for Public Linear projects is determined as follows: Required Water Area of New or Quality__ Reconstructed x 0.75 — 12 in/ft Treatment Impervious [in] [in/ft] Volume [ft3] Surface [ft2] draft 06-15 ECS Ordinance.docx 18/29