Agenda - Public Works Committee - 06/21/2016

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162nd Lane West of Ramsey Boulevard 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 up to 20 feet higher than the wetlands. 156th Lane East of TH 47/Saint Francis Boulevard 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 155th 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 156th 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 septic system drain field. The City paid to have the drain field relocated outside of the drainage easement. The water was contained within the drainage and utility easement in 2014. On March 31 st the Public Works Committee determined it would be cost-prohibitive to address all drainage concerns throughout the City. It was therefore confirmed that the Gibbon Street area was experiencing the most significant issues and that Staff should research drainage solutions for this area first,and that the results of the research should be brought back to the Public Works Committee for further consideration. Attached are minutes from the March 31,2015 Public Works Committee meeting for reference. On June 16,2015, Staff presented four possible options for alleviating localized flooding issues in the Gibbon Street area to the Public Works Committee. A figure showing the location, alignment and profile view of each of the four options is attached. Minutes from this meeting are also attached. The four options are as follows: Option 41:This option requires installing a pipe in an existing drainage and utility easement. The initial plan was to install approximately 800 feet of pipe by jacking to avoid large trees within the easement and cutting a deep trench through Iguana Street. This was determined to be infeasible after further investigation for the following reasons. The jacking pit would need to be placed in one wetland and the receiving pit and pipe fusing area would need to be in the second area. Both areas are over 400 feet from the nearest road. Access would require acquisition of additional easements. The fused pipe may tend to sink into the wetland prior to being pulled back. The City did a project in 2012 where the boring machine was placed on upland in an existing easement extending to the street. The welding of the pipe was done on planking extended from an existing road. The jacked length was approximately 800 feet. The total project cost was$160,000. The Gibbon street project would require additional easements and restoration of all disturbed lawn surfaces. Option 92:This option requires cleaning the existing County Ditch that runs north of this development. This option is not feasible because it would require lowering the existing surface area of some wetlands up to 2 feet which is not permitted under the Wetland Conservation Act. Option 43: This option considered the suggestion of the property owners at 17421 Gibbon Street NW for using a different set of drainage and utility easements to provide drainage to the west. Evaluations of this route indicated that there are two high areas that would need to have pipe installed and that there is minimal elevation difference between the beginning and ending points. This route is not feasible. Option 44:This option considered extending storm sewer pipe south in the Gibbon Street right-of-way,then west along the 173rd Avenue right-of-way to provide positive drainage from the area to County Ditch 66. This appears to be feasible. The location and elevation of existing small utilities along the route would need to be determined during final design to better define the scope of this process. The normal water level of the existing wetland east of Gibbon Street would also need to be explored in detail during final design. This option was estimated to cost between$275,000 and$300,000,which does not include the acquisition of easements which would be determined during final design.