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it Planning Commission 471-97: O'Neil Property March 8, 1997 Page 13 established along the new water edge. The amount of groundwater interaction is not expected to change. Wetland Buffer: The City of Mounds View has an adopted a wetland zoning district which. establishes a 100-foot buffer area abutting identified wetlands. Grading and construction in the buffer area requires approval of a wetland alteration permit. These permits may be granted as long as certain criteria were met, drainage controlled and the adjacent wetland was protected from degradation. The applicant is proposing to build a portion of the theater building and both detention ponds in the wetland buffer. The buffer area is shown with a dotted line on the site plan. Detention ponds are typically placed in the buffer area since they need to be close to the wetland. They usually revegetate so they continue to provide a"natural" buffer for the wetland. Encroachment of buildings into buffer areas creates less problems than parking lots because the runoff is cleaner. Staff regards the encroachment of the theater building into the buffer as workable if the area between the building and the wetland is left natural, so the vegetation will continue to provide a filtering and screening effect. • ■ Drainage The City Engineer has provided a review of drainage issues associated with this project (see Attachment 7). The drainage system is designed to collect the water from the developed portion of the site, run it through the detention ponds to allow settling of pollutants, and then discharge the water into the wetland. The wetland drains through a 15" pipe into the storm sewer system in Long Lake Road. Development of the project will result in higher water levels in the wetland (0.2 feet in a 10 year storm; 0.3 feet in a 100 year storm). The increased water elevation will not have a negative impact on adjacent structures or roads; the water will remain on the site. The rate of runoff into the storm sewer on Long Lake Road is constricted by the size of the pipe. The City Engineer recommends that the pipe size be left as is, since enlarging it would cause capacity problems downstream and there is enough room to store water in the wetland. Residents south of the O'Neil property have expressed concerns that this development will increase existing problems with flooding in their backyards. The City Engineer reviewed this situation and responded that the localized flooding south of County Road H2 is not affected by the O'Neil property, even with development. Also, according to Al Sunderman, a groundwater specialist in the City Engineer's Office, there should not be any impacts to the existing groundwater table in the area. The effect of converting woods or open space to impervious surfaces is that it will reduce potential groundwater recharge areas. In this case, however, the water will be diverted to the wetland and thus the net impact should be little change in the current recharge potential of the area. It is the City IIIP Engineer's view that flooding in the neighborhood is being caused by upstream drainage from the north side of Highway 10 overloading the existing storm drain system in the