Consider Sanitary Sewer Options for the Property Located at 5220 156th Lane NW

The Woodland Green Subdivision, located east of TH 47 south of the Boy Scout Camp, was platted in 1973.  Lot 4, Block 3 (5220 156th Lane NW) was platted with a 75 ft drainage and utility easement across the back of the lot.  The owners of the lot applied for a building permit in 1988, and since the back of the proposed house was shown at the platted easement line they applied to the City to vacate 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 (see attached).

The Wildlife Sanctuary subdivision was platted on the west side of TH47 in 2002, with the stormwater from the development discharging into the adjacent wetland.  An equalizer pipe was placed under TH47 and storm sewer pipe was installed along 155th Lane and Barium Street in 2003, with the ultimate stormwater discharge to the wetland adjacent to Woodland Green park located at the rear of 5220 156th Lane.  The Highlands at River Park subdivision was platted in 2001 (located to the east of Woodland Green); which included a storm sewer pipe that connected the Woodland Green park pond to an existing pipe west of Juniper Ridge Drive, and this existing pipe discharges to the Rum River (see attached area overview map).

The property owners at 5220 156th Lane NW, Jason and Ruth Obermaier, contacted the City at the end of June/beginning of July regarding standing water in their back yard; and specifically the potential impacts to their septic drainfield in that location.  City staff visited the site to collect some survey data and verify elevations on the downstream storm sewer system to ensure that the water was flowing properly.  Based on a septic system sketch in the City's property records it appears that the drainfield is constructed entirely outside of the City's 25' drainage and utility easement, and the water elevation at the time was approximately 3' - 5' outside of the drainage and utility easement and potentially over one lateral of the drainfield (see attached lot detail sketch).

This item was discussed at the Public Works Committee in July, and several options were discussed relative to the downstream storm sewer system, and potential modifications for improved long term drainage to the Rum River; including enlargement of ponds, lowering of existing storm sewer pipe, and installation of additional storm sewer pipes.  The recommendation from that meeting was to address the immediate concern related to the septic system, and evaluate options to correct this matter such that additional easements could be reacquired in this location.

Option 1
There is room to install a finger of the drainfield closer to the house; however current regulations require 3 feet of vertical separation between the invert of the drainfield pipe and saturated soils.  It is unlikely this requirement could be met under the current condition, since the water table is approximately the same elevation as the surface water and this area has been inundated on several occasions.

Option 2
The existing well that serves this property 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 (along with considerable grading efforts), and a pump would be required to lift the discharge from the existing septic tank to the drain field.  The property owner has stated they are not interested in this option, as they want to preserve the existing conditions on their property (trees, swimming pool, irrigation system, etc.).

Septic tank standards do allow for construction of a mound system over an existing drainfield, and this option was evaluated for size and cost considerations.  The mound system would need to be approximately 40' wide x 80 long x 5' high, and is estimated to cost $15,000 - $18,000.  Additional items that would also need to be completed with this approach include; the installation of fill material and grading to raise the grades at the rear of the property (to reduce water flow outside of the City easement in the future), restoration work (turf establishment and irrigation revisions), and the vacation of additional easement because the 40' dimension on the mound width would extend approximately another 10 feet in the remaining 25 foot easement retained by the City.  Due to the need for additional easement vacation, and placing the new drainfield within the area adjacent to this further reduced easement, staff is not supportive of this option.

Option 3
Staff evaluated the option for connected the property to the City's municipal sanitary sewer system; which includes directional drilling of a force main to the existing septic tank on the property, pipe materials, restoration, a pump and vault at the septic tank to lift the discharge to the city system (due to grade constraints), road work (bituminous removal and patching), and connecting to an existing manhole.  This item is currently be estimated, and additional information will be provided at the meeting.  The property owner is also concerned with the service charge for this connection (currently $67 per month).

The funding source for these potential improvements would most likely be the City Stormwater Utility Fund.