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In the fall of 2011, City staff contracted out the investigation of all the significant areas of flooding concern to Hakanson Anderson. The goal was to have an independent third party evaluate the areas, provide options for corrective actions, and associated estimates to implement the work. They completed their analysis and compiled a report that references potential solutions for each area identified (see attached final report). This report was introduced in general terms at the February 2012 Public Works Committee meeting, with the direction being that staff would come back before the committee over the next several months to discuss the merits of each potential improvement in more detail. This case will focus primarily on section one (148th Lane) and section two (149th Lane) of the report. 148TH LANE NW The site is east of Nowthen Boulevard (CSAH 5), southeast of Ramsey Elementary School. There is a low area across three (3) lots south of 148th Lane, that was created as a stormwater pond for the area and wetland mitigation for the development. There is a storm sewer inlet to this area along the west edge, which drains the subdivision to the north. There is also an outlet from this area on the east end that has an invert elevation approximately 2.5 feet above the low point in the basin. The outlet pipe connects to a manhole in the boulevard south of 148th Lane, which also takes storm water runoff from the roadway; this structure directs both of these flows to the east and into a downstream receiving body in the City's stormwater system. The inverts on both pipes in the manhole are at approximately the same elevation, and therefore water may be entering this basin that is not intended to flow there from the stormwater system. It was also observed that the basin has several undulations in the ground surface that do not allow the water to evenly spread out across the entire drainage and utility easement; basically there appears to be three separate, somewhat isolated basins. Hakanson Anderson explored several options for installing another outlet and determined that each option would not significantly affect the high water elevation in the basin, nor justify the costs associated with performing them. Additional easements would need to be acquired, and disruption of neighboring properties would occur. For this project staff is proposing to install a check valve in the storm pond outlet to block drainage from the street and only allow water to exit the basin through this structure, thereby eliminating additional flow to the area. It is also planned to regrade the area at the rear of these three properties to restore the contours originally designed for the basin. 149TH LANE NW This area is west of TH 47 and east of 149th Lane, and the area in question is adjacent to the large DNR wetland that abuts TH 47. The City Council accepted a petition on August 23, 2011 that was initiated by the resident at Lot 3, Block 1, Ramsey Meadows 4th Addition (5410 149th Lane NW). The homeowner contacted the City about water standing in their backyard. Review of the grading plan indicates this area was part of the wetland mitigation plan prepared for the plat and is controlled by Wetland Conservation Act rules. There is a draintile present across the neighboring lot to the south that connects this backyard to the DNR wetland. Stormwater and/or groundwater have flowed into the backyard, which is lower than the wetland in locations, and drainage and utility easements are recorded over this area on the property. The DNR lists the normal water level of the wetland as 860.0, and there is a retaining wall with steps in the backyard with an elevation on the lowest step at approximately 860.1 The backyard slopes down to the east, away from the retaining wall, so there may be water present when the wetland is at normal elevation. There is an outlet pipe under TH 47, with an outlet structure that controls the water elevation in the wetland. The lowest opening of the outlet structure was approximately 2 1/2 feet above the normal water elevation of the wetland at the time the elevated water concern was reported last summer. This structure was quickly modified to lower the outflow elevation, in an attempt to alleviate the high water concern, and the invert from the wetland is now approximately 10 inches above the normal water elevation. For this project staff is proposing to remove the outlet control structure and 8 feet of pipe. We then propose to remove vegetation around this location, that may be impeding flow, and reinstall another section of pipe to create a flared end section outlet with an invert elevation of approximately 860 (the normal water level of the wetland). DIVISION A CHANGE ORDER