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City of Arden Hills when those responsibilities are legally transferred to another party; and (iii) Are designed to protect/preserve structural stormwater BMPs. If structural stormwater BMPs change causing decreased effectiveness, new, repaired, or improved structural stormwater BMPs must be implemented to provide equivalent treatment to the original BMP. D. Permanent Stormwater Management System Design Criteria 1. Infiltration System (i) Infiltration options include but are not limited to: infiltration basins, infiltration trenches rainwater gardens,bioretention areas without underdrains swales with impermeable check dams, and natural depressions; (ii) To determine if an infiltration system is suitable, either the MPCA's contamination screening checklist must be completed or an assessment must be conducted. The checklist or assessment must be documented in the site plan For more information and to access the MPCA's "contamination screening checklist" see the Minnesota Stormwater Manual; (iii) Must be designed such that pre-existing hydrologic conditions of wetlands in the vicinity are not impacted e.g., inundation or breaching a perched water table supporting a wetland); (iv) Must not be excavated to final grade, or within three(3) feet of final grade, until the contributingdrainage rainage area has been constructed and fully stabilized unless they provide rigorous erosion prevention and sediment controls (e.g., diversion berms)to keep sediment and runoff completely away from the infiltration area. (v) When excavating to within three(3) feet of final grade, the Permitee must stake off and mark the area so heave construction vehicles or equipment do not compact the soil in the infiltration area; (vi) A pretreatment device such as a vegetated filter strip, forebay, or water quality inlet(e.g., grit chamber) to remove solids floating materials, and oil and grease from the runoff, to the maximum extent practicable, must be used before the system routes stormwater to the infiltration system; (vii) Designed to provide a water quality volume as described in Section b.iii, b.iv, and b.v; (viii) Designed to discharge all stormwater(including stormwater in excess of the water quality volume)routed to the system through the upper most soil surface or engineered media surface within 48 hours. Additional flows that cannot infiltrate within 48 hours must bypass the system through a stabilized discharge point; (ix) Must provide a means to visually verify the infiltration system is discharging through the soil surface or filter media surface within 48 hours or less; Page 3 of 7