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Pamela Sheldon May 22, 1997 Page No. 211110 go through a portion of the wetland which may be protected by the DNR. If this is the case, it may be more difficult to obtain a permit to fill or excavate in the wetland. The central pond appears to be correctly located,but we questioned how the water from the Condo Building parking lot and drive area would get to the central pond. As proposed, it would need to go through the building or around the back side. A better solution may be to construct a pond in the southwest corner of the property. Based on the information provided by the developer, the proposed pond volume requirement was 0.79 acre-feet. This is based on a runoff factor for the entire site excluding the wetland and the existing office building. Another way to calculate the required volume is to look at the runoff from the directly connected impervious surfaces (those which go directly to the pond without going over grass or pervious surfaces) as one area, and add it to the runoff from the rest of the area. Based on this criteria,the required volume is 0.93 acre-feet. The required area for the 0.93 acre-feet of storage is about 130 feet by 130 feet or about 0.4 acre of land(assumes 8-foot deep retention pond and 4-foot deep detention pond). If the 0.79 acre-feet is used as the criteria, the required size for the same pond depth is 125 feet by 125 feet or about 0.35 acre. These area requirements are larger then proposed for the central pond area. Conclusions: 1. The west pond appears to be in an unfeasible location. • 2. The central pond may need to be larger 3. A new pond may be required for the Condo Building. 4. A new pond may be required on the east end of the property next to the proposed office building on the north side of the wetland. Wetland Buffer Many areas of the project are within in the 100 foot buffer. The revised wetland boundary has reduced the impacts; however, there may still be parking lots and other potentially damaging land uses within the buffer. Building roofs and sidewalks are also in the buffer, but have much less impact to the wetland if runoff from these surfaces goes directly into the wetland. During the final plan, more care should be taken so that parking lots and other potential pollution sources are not in the buffer area. We recommend, due to the potential for a limited buffer area, that a special easement be obtained between the wetland and the development. This will assure City control of the area to maintain the area as a natural buffer. Conclusions: 1. The proposed building site encroaches in the wetland buffer area. 2. Sediment ponds are proposed to mitigate potential pollutants to the wetland and would need to be properly sized in the final plat submittal. 3. Final buffer area appears to be less then the 100-feet in the City ordinance; therefore, the City should obtain a conservation easement for the buffer area to assure it is not mowed and remains a natural buffer. •