Agenda - Public Works Committee - 06/21/2016

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Public Works Committee 5.2. Meeting Date: 06/21/2016 By: Bruce Westby,Enginecring/Public Works Title: Review Updated Estimated Costs for Sunfish Lake Sedimentation Basin Improvements Purpose/Background: Purpose: The property owner at 14520 Sunfish Lake Drive NW is requesting that the City reconstruct specific stormwater treatment improvements impacting a portion of their back yard. The requested work includes constructing a settling basin at the end of the storm sewer outlet from Sunwood Drive where it intersects 145th Lane NW for the purpose of reducing the frequency and volume of stormwater runoff running through the existing drainage Swale along their rear lot line, and removing the existing cattails and other types of vegetation commonly found in wetlands from the Swale and restoring the Swale to a lawn type condition using sod, though seeding could be acceptable if done correctly.Attached Figure 1 shows 2014 aerial photography of the property and the surrounding area including parcel lines,property addresses, and street names, and identifies the locations of the Swale and various storm sewer outlets in relation to the property. Attached Figure 2 shows the concept design for the requested improvements. Background: The property owner at 14520 Sunfish Lake Drive NW has contacted the City on numerous occasions since the mid-2000's regarding a drainage Swale located within a 20-foot wide drainage and utility casement that runs across the back edge of his lot. The lot backs up to Sunfish Lake. The lake border adjacent to the property is predominantly cattails,and the edge of open water is approximately 100 yards northwest of the property. This property is located in the Sunfish Lake Estates subdivision which was platted in 1996. The plat dedicated the 20-foot drainage and utility casement parallel to the rear lot line to accommodate a drainage Swale that connects the storm sewer outlet from Sunwood Drive to an outlet control structure located near the southwest corner of the lot. Attached is a certificate of survey that shows the lot boundaries and locations of the rear lot drainage casement and berm along the back side of the Swale. The drainage Swale and outlet control structure are not shown on the final Grading and Utility plans filed for the plat. The structure and the Swale are shown on the plans the City prepared for the extension of Sunwood Drive. A copy of this plan is attached. City files show that the City constructed Sunwood Drive around the time the plat was filed. This provided access to the site. An EAW was required prior to construction of Sunwood Drive. The Minnesota Department of Natural Resources(DNR)provided a response letter noting that the stormwater from the roadway should not be discharged directly to the wetlands adjacent to the roadway. A copy of this letter is attached with this text highlighted in yellow. The as-built plans for Sunwood Drive show that the storm sewer is directed to the Swale on the back side of the lot. This Swale provides treatment for the stormwater runoff from Sunwood Drive prior to discharging the runoff into Sunfish Lake via the outlet control structure. According to the property owner,they were able to mow the Swale and outer berm for the first several years after moving in around 1999, and standing water first appeared in the Swale in the mid to late-2000's with the frequency of standing water increasing over time. The property owner contacted the City about the standing water in the late-2000's, after which Staff visited the site and informed the property owner that the Swale was designed for this purpose, and that the drainage and utility casement was sized to accommodate the water.