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Mounds View City Council February 9, 2009 Regular Meeting Page 6 • 11. REPORTS A. Reports of Mayor and Council. Council Member Mueller announced that the Concerned Citizens of the North Metro will hold a meeting regarding the Anoka County Blaine Minor Airport on Tuesday, February 24, 2009, from 7-9 p.m. at the Spring Lake Park City Hall. Council Member Gunn commented on the success of the Irondale High School Dance held on Saturday night at the Community Center. B. Reports of Staff. 1. Report from Bonestroo Regarding Design Issue on the County Road 10 Trail Segments 1-5. Joe Rhein, Consulting Engineer with Bonestroo, advised of the elevation issues found to be present with the trail segment along the north side of CR 10 just west of Wooddale Drive. The Rice Creek Watershed District (RCWD) indicated that drainage in this area would more directly impact Rice Creek and determined to require rate control with this project. Mr. Rhein presented a diagram of the subject area, trail alignment, and explained the drainage direction. He stated the open ended storm drainage pipe in the ditch can be improved with a structure with a reduced opening to satisfy the rate control for less than $3,000 on this $800,000 project. However, detailed storm water modeling was required to prove the rate control to the RCWD. That modeling cost about $4,000 and identified that the pond and ditch are hydrologically connected so during large storm events, the pond water would overtop about 250 feet of the trail. During a 50-year storm event, the maximum water depth on the trail would be 3.5 inches for about an hour and 10 minutes. Then the storm sewer would drain away the water and the pond elevation would go down below the trail elevation. During a 100-year storm event, the maximum water depth over the trail would be 9 inches and appear to be one pond area. This would last for 2.5 hours and then the water would recede to be lower than the trail. Mr. Rhein advised there is a 2% chance during any given year that 50-year event will occur and a 1 % chance that a 100-year event will occur. Mr. Rhein stated if the Council deems this condition acceptable, recognizing the trail may become overtopped during certain heavy storm events but dry after the storm event, no action was needed, there would be no additional cost or delay in the project. If the Council deems this condition to not be acceptable, staff can investigate the option of raising the elevation of the trail 6 to 10 inches so it is above the overflow elevation during peak storm event. Since this would result in additional wetland impacts, permitting through the DNR, Army Corp of Engineers, and RCWD would be required. The cost is estimated to be $20,000 to $25,000 to repeat the permitting process, purchase additional wetland credits from the State's wetland bank, and to construct a trail berm that is raised by ten inches in height. In addition, the project schedule would be delayed one month and there is no guarantee reviewing agencies would approve the added wetland impact. •