Consider Stormwater Improvements on 148th Lane NW and149th Lane NW, and Approve Change Orders for City Improvement Project 12-24

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 sand plain.  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.  A summary was presented that outlined 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 staff 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 dedicated drainage & utility easements (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 a larger stormwater improvement plan set.  Staff finalized plans for all these items, including incorporation of additional items that were approved at the Public Works Committee meeting in March of 2012, and bid them under two separate contracts, which were awarded by the City Council on May 22, 2012.

The final three areas of flooding concern from 2011 were discussed by the Public Works Committee on May 15, 2012, with the recommendation being to perform corrective actions on all three this year.  These items were included in the report from Public Works on the consent agenda earlier this evening, and include the Rum River Hills Gold Course, 148th Lane NW, and 149th Lane NW.  City staff has prepared plan sheets for the corrective actions contemplated for both 148th Lane and 149th Lane, and has received quotes from the two storm sewer improvement contractors that are already working in the City.  The Rum River Hills Gold Course will be handled as a separate case on this evenings agenda.

The property owners that may be affected by these project were notified of the meeting and have received a copy of the agenda.

In the fall of 2011, City staff contracted out the investigation of all the significant areas of flooding concern to Hakanson Anderson.  The goal was to have an independent third party evaluate the areas, provide options for corrective actions, and associated estimates to implement the work.  They completed their analysis and compiled a report that references potential solutions for each area identified (see attached final report).  This report was introduced in general terms at the February 2012 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.  This case will focus primarily on section one (148th Lane) and section two (149th Lane) of the report.

148TH LANE NW

The site is east of Nowthen Boulevard (CSAH 5), southeast of Ramsey Elementary School.  There is a low area across three (3) lots south of 148th Lane, that was created as a stormwater pond for the area and wetland mitigation for the development.  There is a storm sewer inlet to this area along the west edge, which drains the subdivision to the north.  There is also an outlet from this area on the east end that has an invert elevation approximately 2.5 feet above the low point in the basin.  The outlet pipe connects to a manhole in the boulevard south of 148th Lane, which also takes storm water runoff from the roadway; this structure directs both of these flows to the east and into a downstream receiving body in the City's stormwater system.  The inverts on both pipes in the manhole are at approximately the same elevation, and therefore water may be entering this basin that is not intended to flow there from the stormwater system.  It was also observed that the basin has several undulations in the ground surface that do not allow the water to evenly spread out across the entire drainage and utility easement; basically there appears to be three separate, somewhat isolated basins.

Hakanson Anderson explored several options for installing another outlet and determined that each option would not significantly affect the high water elevation in the basin, nor justify the costs associated with performing them.  Additional easements would need to be acquired, and disruption of neighboring properties would occur.  For this project staff is proposing to install a check valve in the storm pond outlet to block drainage from the street and only allow water to exit the basin through this structure, thereby eliminating additional flow to the area.  It is also planned to regrade the area at the rear of these three properties to restore the contours originally designed for the basin.

149TH LANE NW

This area is west of TH 47 and east of 149th Lane, and the area in question is adjacent to the large DNR wetland that abuts TH 47.  The City Council accepted a petition on August 23, 2011 that was initiated by the resident at Lot 3, Block 1, Ramsey Meadows 4th Addition (5410 149th Lane NW).  The homeowner contacted the City about water standing in their backyard.  Review of the grading plan indicates this area was part of the wetland mitigation plan prepared for the plat and is controlled by Wetland Conservation Act rules.  There is a draintile present across the neighboring lot to the south that connects this backyard to the DNR wetland.  Stormwater and/or groundwater have flowed into the backyard, which is lower than the wetland in locations, and drainage and utility easements are recorded over this area on the property.  The DNR lists the normal water level of the wetland as 860.0, and there is a retaining wall with steps in the backyard with an elevation on the lowest step at approximately 860.1   The backyard slopes down to the east, away from the retaining wall, so there may be water present when the wetland is at normal elevation.

There is an outlet pipe under TH 47, with an outlet structure that controls the water elevation in the wetland.  The lowest opening of the outlet structure was approximately 2 1/2 feet above the normal water elevation of the wetland at the time the elevated water concern was reported last summer.  This structure was quickly modified to lower the outflow elevation, in an attempt to alleviate the high water concern, and the invert from the wetland is now approximately 10 inches above the normal water elevation.  For this project staff is proposing to remove the outlet control structure and 8 feet of pipe.  We then propose to remove vegetation around this location, that may be impeding flow, and reinstall another section of pipe to create a flared end section outlet with an invert elevation of approximately 860 (the normal water level of the wetland).

DIVISION A CHANGE ORDER

Additionally, due to the significant rainfall that has occurred throughout the month of May, water levels are elevated in all locations that some improvements are planned for.  Under Division A of the Stormwater Improvement Project, a couple of modifications are being proposed.  A culvert was initially proposed to be installed under 175th Avenue NW (Old County Road 63) to alleviate flooding concerns on the roadway that occur from time to time; there is currently no culvert in place that allows water to flow south to north.  After reviewing the downstream area following the recent extreme rainfalls it was determined that work needs to be performed on the downstream brooks and ditches to adequately allow for this water to eventually reach Trott Brook.  Therefore, this portion of the overall project is now proposed to be eliminated (deduct) from Division A, and staff will begin meeting with property owners in the area to review this drainage concern and seek approval to perform a ditch cleaning project.  Once the downstream drainage has been resolved then we can revisit this culvert installation in the future.  Attached to this case is a location map showing this drainage area.

The elevated water levels in County Ditch 66 are causing the culverts to flow full through the area near Wolfram Street.  Division A of the contract contemplated an 18" bypass culvert to be installed while the existing failing 48" culvert is being replaced.  Due to the high water levels and extreme flows a larger bypass system is needed to maintain the integrity of the channel and roadway during installation of the new culvert.  Therefore a change order (addition) is being requesting for this additional work.  Attached to this case is the requested change order for the above described work, which results in a net deduct change order for Division A of the 2012 Storm Sewer Improvement Project (IP #12-24) in the amount of $119.

The funding source for these improvements is proposed to be the Stormwater Utility Fund.  Staff has received quotes from two existing contractors, so as to include this work as a change order under a contract for City Improvement Project 12-24; 2012 Storm Sewer Improvements.  The engineers estimate for the two projects is $21,000, and the results of the quotes are as follows:
 

Dryden Excavating (Division A contractor)           $16,610.00
Julian Johnson (Division B contractor)                  $16,460.00

Staff recommends approving a change order for City Improvement Project 12-24 - Division B, with Julian M. Johnson Construction in the amount of $16,460.00

Motion to approve a change order for City Improvement Project 12-24 - Division B, with Julian M. Johnson Construction in the amount of $16,460.00