Agenda - Public Works Committee - 07/19/2011

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Public Works Committee 5. 1. Meeting Date: 07/19/2011 By: Len Linton, Engineering/Public Works Title: Consider Stormwater Solutions for Woodland Green Pond Background: Woodland Green Subdivision was platted in 1973. The subdivision is located east of TH 47 south of the Boy Scout Camp. Lot 4, Block 3 was platted with a 75 ft drainage and utility easement across the back of the lot. This lot is 5220 156th Lane NW. The owners of the lot applied for a building permit in 1988. The back of the proposed house was at the easement so they applied to the City for vacation of the North 50 feet of the easement, leaving a 25 ft drainage and utility easement across the back of the lot. The vacation was approved by resolution of the City Council. The conditions of the resolution were: 1. The north 50 feet of the drainage and utility easement was vacated. 2. The south 25 feet of the drainage and utility easement was retained by the City. 3. The applicant reimbursed the City for all expenses involved in the vacation of the drainage easements. Wildlife Sanctuary subdivisions were platted on the west side of TH 47 in 2002. The storm water discharged into the wetland on the west side of TH47. An equalizer pipe was installed under TH47 and storm sewer pipe was installed in 155th Lane and Barium Street in 2003. This pipe discharges to the wetland adjacent to Woodland Green park and 5220 156th Lane. Highlands at River Park subdivision was platted in 2001 to the east of Woodland Green. A pipe was installed connecting the Woodland Green pond to an existing pipe west of Juniper Ridge Drive. This existing pipe empties into the Rum River. This is shown on the Area Overview Map. The residents at 5220 156th Lane, Jason and Ruth Obermaier, contacted the City about water standing in their back yard. They were concerned the standing water would impact their drainfield. City staff visited the site in June 2011 and shot elevations in their back yard. We also shot the water elevation at the pond outlet and at the pipe crossing under 156th Lane west of Juniper Ridge Drive. Based on City Records the drainfield is constructed outside of the 25 ft drainage and utility easement. The water is outside the drainage and utility easement and over one lateral of the drainfield. This is shown on the Lot Detail map. Notification: Observations: There are several options for addressing the issue of water ponding on the drainfield. They are 1) relocate the drainfield on the lot, 2) enlarge the pond in Highlands at River Park and 3) lower the existing storm sewer north of 156th Lane. Option 1 There is room to install a finger of the drainfield closer to the house; however, current regulations require 3 ft vertical separation between the pipe and saturated soils. It is unlikely this requirement could be met. The well is located on the east side of the house so a relocated drainfield would need to be placed on the west side of the house to maintain proper separation. The lot slopes from front to back and there are mature trees that would need to be removed. A lift pump would be needed to get the water from the septic tank to the drain field. The septic tank standards do allow for construction of a mound system over and existing drainfield. This would provide the needed vertical separation. The estimated cost for this work is $20,000. Option 2 The existing ponding area (Pond B) between North Yakima Court and 156th Lane could be enlarged to provide