Agenda - Public Works Committee - 03/31/2015

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north and extend onto the 2 nd lot to the north. The address of the parcel with the majority of the wetland is 17511 Gibbon Street. There is a drainage and utility easement on the west side of Gibbon Street that connects to the easements on the Wildwood Acres plat. West of the Wildwood acres plat is an un-platted parcel. A County Ditch runs through this parcel. There is a drainage and utility easement on the west side of Gibbon Street across from the wetland at 17511 Gibbon Street. This easement also connects with the easements on Wildwood Acres. Staff selected 2 alignments to evaluate, the first starts at 17421 Gibbon Street and runs west through drainage and utility easements, through Wildwood Acres, crossing Iguana Street and ending at the County Ditch. There is a stretch of approximately 500 feet at Iguana Street that is up to 10 feet higher than 17421 Gibbon Street. The grade slopes down to the west from the high point into the ditch. The grade drops below the beginning elevation 950 feet from the origin. The second alignment starts at 17540 Gibbon Street, runs west then north across Wildwood Acres then crosses un-platted property before turning east and running across Deerwood along another County Ditch then runs south and east across more un-platted property following the ditch to the intersection with County Road 5, Nowthen Boulevard. This is a distance of 2.6 miles. The grade along the profile rises for approximately 500 feet then is level for another 1300 feet. The elevation drops below the beginning elevation 3500 feet from the origin. 162nd Lane West of Ramsey Blvd. This area is un-platted and does not have drainage and utility easements. The residents at 6855 162nd Lane NW contacted the City about the high water elevation in the adjacent wetland. There are a series of wetlands in the back yards north of this parcel. All of the surrounding area is higher than these wetlands. Staff selected 3 alignments to evaluate. The first starts at the property, runs northwest along 162nd Lane, turns south on Jasper Street to 161 st Lane then runs west to Olivine Street then runs southwest to County Ditch 66. The County ditch is slightly higher than the starting elevation. The remainder of the profile is up to 20 feet higher than the starting elevation. This alignment is 3700 feet long, The second alignment starts at the property, runs southeast along 162nd Lane, turns south on Ramsey Boulevard and stays on Ramsey Boulevard to the Ditch 66 crossing. The County Ditch is approximately the same elevation as the starting point. This profile is up to 20 feet higher than the starting point. The third alignment runs along the second alignment to Ramsey Boulevard, crosses Ramsey Boulevard then runs southeast along common lot lines towards County Ditch 66. The profile drops below the starting elevation approximately 1800 feet from the origin. This profile is up to 30 feet higher than the starting point. 156th Lane East of TH 47/St Francis Blvd. This area is platted and has some drainage and utility easements. The residents at 5220 156th Lane NW contacted the City about the level of the pond in their back yard. The ponding area did not have an outlet when the plat was recorded in 1973. A pipe was installed under TH 47 in 2003 to provide a stormwater outlet from a new subdivision. A pipe was also installed along 155h Lane and along lot lines from the wetland east of TH 47 to this pond. An outlet for this pond was installed with the Highlands at River Park Project in 2003. This pipe outlet is lower than the pipe installed with the Reilley Estates plat in 1978. The pond at 5220 156h Lane NW does drain; however, the water level has to be higher than the invert of the pipe downstream The previous owners of the property came before the City Council in 2011 concerned about the proximity of the standing water to their drainfield. The City paid to have the drainfield relocated outside of the drainage easement. The water was contained in the drainage and utility easement in 2014. Staff evaluated 2 alignments for lowering the invert of the existing pipe. The first would involve removing and replacing approximately 1100 feet of existing storm sewer pipe. The pipe is up to 15 feet deep, it is in easements across back yards; however, these yards are wooded and in some cases landscaped. The second alignment considered starting where the pipe crosses 156th Lane, running east along 156th Lane to Juniper Woods drive then following Juniper Woods Drive to the intersection with the existing pipe. This would require 900 feet of pipe with up to 20 feet of cover. Open cutting for pipe installation would require reconstruction