Agenda - Public Works Committee - 03/31/2015

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of the street and would require closing the road for an extended period of time. Timeframe: Staff is presenting an overview of the concerns and potential solutions at this meeting. Detailed analysis will be undertaken as directed by City Council. Observations/Alternatives: Staff offers the following observations on each area: Gibbon Street north of 173rd Avenue This area is relatively flat. The affected area is lower than the potential overland drainage route. The northern route is a county ditch that was excavated through the wetlands prior to the Wetland Conservation Act being passed. Lowering the grade of the ditch to provide drainage to the Gibbon Street Properties would most likely result in draining the wetland which is not permitted. The southerly route would require placing a pipe through an area that is up to 10 feet higher than the affected properties. The existing easements are not wide enough to support open trenching of a pipe. This route may also involve ditching through a wetland which is not permitted. The Wetland Conservation Act may preclude acting on either of these alternatives. The City cleaned County Ditch 66 as part of a sanitary sewer extension project in 2007. Sheet piling weirs were required to be installed at regular intervals in the cleaned ditch. The tops of the weirs were set to maintain the existing wetland elevations. If the existing wetland levels are higher than the area to receive relief then the project is not feasible and other alternatives will need to be studied. 162nd Lane west of Ramsey Boulevard. The affected property is in a natural depression and is surrounded by areas that are up to 20 or more feet higher. This area is un-platted. The westerly route and southerly routes are along road right of way. Open trenching of the pipe would require significant road reconstruction and would also require easements at the end of the routes across private property to discharge to the ditch. The initial review indicates the ditch elevation may be higher that the starting elevation for both of these routes. The easterly route follows road right of way to Ramsey Boulevard then would require easements across private property and would include ditching of a wetland. The wetland rules would also apply any ditching required. 156th Lane east of TH 47 There is an existing storm sewer system that provides drainage for this area. The older part of the system was installed first, adjacent to the Rum River. The pond on the subject property was land -locked when the development was platted. A storm sewer outlet was installed when the property to the east was developed. The end of the new pipe had to be installed lower than the end of the existing pipe. This results in water standing in Woodland Green park and in the adjacent drainage and utility easements until the water rises to a point where it can flow through the system. In all three instances it my be possible to directionally bore a pipe to provide drainage; however, the vertical difference between the starting point and ending point is very small and is close to the vertical tolerance available from directional bored pipe. Direction boring is best suited for pressure pipe situations or where there is adequate vertical relief between the start and the end of the pipe. The father of the resident at 5220 156th Lane came forward with a proposal for installing an infiltration pit in the back yard to alleviate the flooding problem. The pond is normally wet every year. There are years such as 2011 and 2014 where the water level rises above the normal level. The presence of water every year indicates that the