09-22-2004 Council Agenda - Laserfiche WebLink

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WCA/CWA Wetland Application Gervais Hills GES Project No. 2004.040 June 16, 2004 Page 4 Replacement of Unavoidable Impacts The unavoidable wetland impact of 0.17 acre will be replaced through the implementation of the on -site compensatory mitigation plan outlined below. Compensatory Mitigation Plan The Wetland Conservation Act requires replacement of drained or filled wetlands at a minimum ratio of 2:1. Assuming 2:1 replacement of the regulated portion of Wetland A equates to a total mitigation requirement for the project of 14,400 square feet (0.33 acre). New Wetland Credit (NWC) of 18,858 square feet (0.43 acre) is being generated by the applicant on the property (Figure 4). The mitigation site includes the creation of three wetland basins which would drain south to north in the eastern portion of the site. The southern of the three basins would measure 9,170 square feet one foot above the Normal Water Level (NWL) of 866'. This square footage measurement does not include the existing wetland area of 1,500 square feet within the mitigation basin. The ultimate wetland boundary is expected to be established at the 867' contour. The maximum bottom elevation of the southern mitigation wetland is 863'. The central mitigation wetland would measure 6,225 square feet one foot above the NWL of 861.5'. Again, this square footage measurement does not include the unregulated excavated existing wetland area of 1,200 square feet within the mitigation basin. The ultimate wetland boundary is expected to be established at the 862.5' contour. The maximum bottom elevation of the central mitigation site is 859'. The northern of the three mitigation wetlands would measure 3,463 square feet one foot above the NWL of 859.3'. This square footage measurement does not include the existing wetland area of 600 square feet which would not be filled or excavated. The ultimate wetland boundary is expected to be established at the 860.3' contour. The maximum bottom elevation of the northern mitigation site would be 859'. All of the proposed wetland areas would be excavated one foot below the desired final grade and then one foot of segregated hydric topsoil from the impacted wetland area would be placed to bring the mitigation area to its desired final grade. Because of the anticipated water depths of the central and southern wetlands, any seedbank of invasive species (such as reed canary grass) should be controlled by the anticipated depth and duration of ponded water. This plan should result in Type 3 shallow marsh and Type 4 deep marsh wetland at the central and northern basins. The saturated zone in the central and southern basins from the NWL to one foot above the NWL and all of the northern basin will be seeded with Minnesota Department of Transportation Mixture 25A Modified