- Meeting Date:
- 07/19/2011
- By:
- Len Linton, Engineering/Public Works
Title:
Consider Stormwater Solutions for Woodland Green Pond
Background:
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 additional storage capacity in the system. The elevation of the outlet pipe under 156th Lane controls the water elevation of this pond and the one adjacent to the subject property. This would require removal of trees and export of soil. The estimated cost for this work is $60,000.
Option 3
The elevation of the pipe under 156th Lane is controlled by the elevation of storm sewer installed as part of the Reilly Estates subdivision. The outfall of this pipe is approximately 14 feet below the elevation of the Pond B. Lowering the outlet elevation of Pond B would require removing and replacing all of the pipe. The pipe is covered in most areas by drainage and utility easements; however, additional easements would be required for removal and replacement of the pipe. There would be significant restoration costs associated with this option, the route passes through a park and landscaped yards, in addition to two street crossings. An alternate may be directional drilling a pipe along the right of way for 156th Lane and Juniper Ridge Drive then connecting to the existing pipe before it enters the river. This pipe would provide flow for smaller events, larger events would continue to flow through the existing storm sewer. The estimated cost for replacing the pipe is $150,000 plus easements. We are working on prices for directional drilling a pipe in the street right of way.
Discussion
Replacing the drainfield would address the immediate concerns of the resident. This could set a precedent for replacing drainfields adjacent to other ponding areas in the city. Enlarging Pond B would provide additional storage in the storm sewer system. Replacing the existing storm sewer or installing an additional pipe would provide long term relief and lower the water level in Pond B which would lower the water level adjacent to 5220 156th Lane.
Funding Source:
Staff Recommendation:
Committee Action:
Attachments
Form Review
| Inbox | Reviewed By | Date |
|---|---|---|
| Kurt Ulrich | Kurt Ulrich | 07/14/2011 03:44 PM |
- Form Started By:
- Len Linton
- Started On:
- 07/14/2011 10:07 AM
- Final Approval Date:
- 07/14/2011