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Table 4. Hvdroperiod Standards <br />Wetland <br />Susceptibility <br />Class <br />Permitted Storm <br />Bounce for 2 -year <br />and 10 -year Event <br />Inundation Period <br />for 2 -year Event* <br />Inundation Period <br />for 10 -year Event* <br />Highly <br />Susceptible <br />Existing <br />Existing <br />Existing <br />Moderately <br />Susceptible <br />Existing + 0.5 -ft <br />Existing + 1 day <br />Existing + 7 days <br />Slightly <br />Susceptible <br />Existing + 1.0 ft <br />Existing + 2 days <br />Existing + 14 days <br />Least <br />Susceptible <br />No Limit <br />Existing + 7 days <br />Existing + 21 days <br />* Duration of 24 -hours for the return periods utilizing NOAA Atlas 14 precipitation data. <br />Source: Adapted from Rice Creek Watershed District 2013 Rules. <br />c. Wetland Susceptibility Class is determined based on wetland type, as follows: <br />1. Highly susceptible wetland types include: sedge meadows, bogs, coniferous bogs, <br />open bogs, calcareous fens, low prairies, coniferous swamps, lowland hardwood forests, and <br />seasonally flooded water basins. <br />2. Moderately susceptible wetland types include: shrub-carrs, alder thickets, fresh (wet) <br />meadows, and shallow & deep marshes. <br />3. Slightly susceptible wetland types include: floodplain forests and fresh wet meadows <br />or shallow marshes dominated by cattail giant reed, reed canary grass or purple loosestrife. <br />4. Least susceptible wetland includes severely degraded wetlands. Examples of this <br />condition include cultivated hydric soils, dredge/fill disposal sites and some gravel pits. <br />d. Exceptions. Rate control criteria of § 1011.011(5) may be waived if the site discharges <br />directly to a water body with large storage capacity (such as a public water) that has a time-to- <br />peak elevation greater than that for an on-site pond and the volume discharged from the on-site <br />pond is negligible, relative to the volume of runoff entering the water body. <br />6) Design criteria. <br />a. Infiltration BMPs. Infiltration BMPs must be designed to provide: <br />1. Adequate pretreatment measures to remove sediment before runoff enters the primary <br />infiltration area; <br />2. Drawdown within 48 -hours or 72 -hours from the end of a storm event, for surface or <br />sub -surface features, respectively. Soil infiltration rates shall be based on the appropriate HSG <br />classification and associated infiltration rates ( <br />draft 06-15 ECS Ordinance.docx <br />20/29 <br />