Consider Storm Sewer Improvements on 163rd Lane - A Continuation of Discussions Related to 2011 Flooding Concerns

Last summer the City experienced several significant rainfall events that lead to many localized flooding concerns, and resident complaints. The large volumes of precipitation that occurred over a short period of time appears to have elevated the groundwater within areas of the City, and prohibited the generous rate of infiltration that typically takes place in the Anoka sandplain. Throughout the summer and fall staff worked hard at registering and responding to the calls, and evaluating the situations on an individual basis to determine whether quick fixes could be implemented (culvert obstructions, re-ditching, etc.) to alleviate the immediate concerns.

This item was discussed at the Public Works Committee on August 15, 2011, and at that time staff summarized the areas of concern that were being investigated based upon citizen complaints received. The attached summary was presented at the meeting; which outlines the concern identified, actions steps to evaluate the concern, additional investigations that would be necessary to fully understand the situation, and recommendations for specific projects that could be implemented rather quickly and inexpensively. At that time we classified the issues into 3 categories:
1. Those that required no further action. They were evaluated and corrected, or did not need correcting because the water was fully contained within a dedicated drainage & utility easement (functioning as designed).
2. Those that required additional investigation and evaluation before deciding on a long term solution, and implementing corrective actions.
3. Those that had an identified recommendation for immediate action.
At that meeting the Committee briefly discussed the areas of concern, and directed staff to prepare plans and specifications for the items identified in category 3. Once this direction was ratified by the City Council on September 13, 2011, and the plans completed, it was too late in the season to secure bids and complete the improvements in 2011. It was then decided to delay construction until 2012, where some of the improvements could be completed by inclusion in the street maintenance program. Staff is in the process of finalizing plans for these items and intends to solicit quotes for the improvements this spring/summer. Depending on the direction staff receives for potential improvements to alleviate some of the outstanding concerns identified over the next couple of months, additional plans can be incorporated into one plan set for bidding.

The residents have been provided with a copy of the agenda and notified of the meeting time.

Staff prepared a brief RFP in the fall of 2011, to investigate the areas of concern, and distributed it to members of the City's consultant pool in the fall of 2011. The goal of this project was to have an independent third party evaluate the areas, provide options for corrective actions, and associated estimates to implement the work. Hakanson Anderson was awarded the project to undertake these investigations, and they have since completed their analysis and compiled a report that references potential solutions for each area identified. Attached to this case is the final report.

This item was introduced in general terms at the February Public Works Committee meeting, with the direction being that staff would come back before the committee over the next several months to discuss the merits of each potential improvement in more detail.

Tonight we would like to focus on a couple of the projects that are located in neighborhoods that are proposed to receive street maintenance activities this summer. I would like to draw your attention to section 4 related to 163rd Lane.

This area is located west of Elmcrest park.  There is an existing landlocked low area south of 163rd Lane and east of Wolfram Street.  During a majority of the year, stormwater runoff infiltrates int the soil. However, during early spring when the ground is frozen and during periods of heavy rainfall, water levels have risen to elevations taht cause flooding of adjacent properties.

Different sized outlet pipes were analyzed to drain the low area.  Installing an outlet will have a significant impact on the high water levels in the area and, most importantly, the length of inumdation will be greatly reduced.  We recommend driectionally drilling an 18" HDPE pipe south to County Ditch #3 with an invert elevation of 872.0  Installing the pipe at an elevation of 872.0 will continue to allow 3" storm events to infiltrate into the soil.  The estimated cost to install this outlet is $80,795.

An easement will be required on the lot to cover the maximum ponding area and the route of the outlet pipe from the pond to the south property line.  The directional drilling may require acquisiton of additional easments along the route of the pipe which can be time consuming.   Construction of the connection to County Ditch #3 may be best done under frozen conditions. The estimated cost of the project exceeds the annually budgeted amount for storm sewer improvements so it may need to be spread over a couple of years.

The plat for this neighborhood, detail of the drainage and utility easement over the low area and the plats between the low point and County Ditch #3 are attached.

In the fall of 2011, while staff was in the process of updating the City's Capital Improvement Program (CIP), we budgeted additional funds to stormwater improvement projects over the next two years in an effort to address some of these concerns. The Capital Improvement Program (CIP) lists a $75,000 annual expenditure for the next 5 years to address city wide drainage enhancements.

Staff recommends adding this project to the list to be evaluated when the Capital Improvment Program is updated.  Easement acquisition, construction timing and budget considerations require additional investigation.

Motion to recommend adding this project to the list to be evaluated when the Capital Improvment Program is updated.