Purpose:
The purpose of this case is to adopt Resolution #20-176 approving plans and authorizing Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project #19-17. 

Background:
The property owner at 5751 164th Lane first contacted Staff regarding drainage concerns on May 11, 2019.  According to the property owner, stormwater runoff from the drainage ditch in City right-of-way in front of their house has been flowing directly across their property in a shallow swale for decades without any drainage easements in place.  The property owner claimed that during the winter of 2018/19 the outer edge of the 14-foot by 16-foot floating concrete slab supporting their attached enclosed patio, which is directly adjacent to the drainage swale running across their property, lifted approximately 6-inches.
 
Staff has not been provided with any evidence that the lifting of the slab actually occurred that winter, such as before and after pictures, but the lifting of concrete slabs can/does occur if/when the soils underneath a slab are subjected to numerous freeze-thaw cycles over time. 
 
After the property owner contacted Staff with their concerns, Staff began working to develop plans to route the stormwater runoff from the public right-of-way through ditches and storm sewer culverts and pipes located within City right-of-ways and drainage easements, instead of across the private property in a swale. After collecting topographic survey information and working with the private utilities, including Northern Natural Gas, who owns and operates two high pressure gas lines that traverse the private property, and the ditches in City right-of-way, staff completed plans and recommends constructing the improvements this fall to ensure no further claims of damage to private property will be received. 
Existing drainage infrastructure includes a culvert crossing under 164th Lane located just west of the driveway to 5751 164th Lane.  Runoff from the south side of 164^th Lane flows though this culvert, which empties into the drainage ditch in front of 5751 164th Lane, and is then routed through a swale on the private property as mentioned earlier.
 
As shown in the attached plans, the drainage improvements proposed with this project involves re-grading the ditch on the south side of 164th Lane and adding a new culvert under 164th Lane at the western lot line of 5751 164th Lane where a drainage and utility easement currently exists and is the intended route for conveying stormwater runoff from this stretch of 164th Lane to the pond to the north. This project will require the replacement of the driveway culvert at 5800 164th Lane.
 
Northern Natural Gas owns a 50’ wide easement which crosses 5751 diagonally and contains two high pressure gas mains. City Staff has had to work with Northern Natural in the design of these plans to avoid conflicts with these gas mains, and has received Northern Natural’s approval of the plans with some contingencies which have been built into the plans.
 
When last meeting with the property owner on February 13, 2020, the owner requested that the City pay for the required repairs to their patio.  On May 4, 2020, a claim was filed by the City with the League of Minnesota Cites Insurance Trust.  At this time it is not known whether LMCIT will pay the claim or not.  This drainage improvement project is proposed to be completed this fall to help avoid any future damages claims by the property owner.
 
Based on the current bid environment Staff anticipates receiving good quotes.  Upon Council approval, Staff proposes to solicit quotes from several local grading contractors with a quote submittal deadline of 10 a.m. on Thursday, September 10th. On September 15th the Public Works Committee can then review quotes and provide a recommendation to the City Council for award of a construction contract on September 22nd.
 
Estimated construction costs for this project total $23,000 and are based on final plans as prepared by City Staff.  Construction staking is proposed to be provided by a consultant at an estimated maximum cost of $3,000.  A proposal for construction staking will be presented to the City Council at the time Staff requests approval of a construction contract to the contractor submitting the lowest quote on September 22nd.
 
All project costs are proposed to be split evenly between the Stormwater Management and Stormwater Utility Funds.  
 
This project is anticipated to take 5 to 10 days to complete, with substantial completion specified for October 23, 2020.  Final payment will be issued in 2021 after turf is established and all work is approved. 

Staff recommends adopting Resolution #20-176 approving plans and authorizing Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project #19-17. 
 
On August 18, 2020, the Public Works Committee discussed this project and ultimately recommended City Council authorization to solicit Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project #19-17.  However, the Public Works Committee asked is Staff had explored the option of simply grading a berm between the front yard of 5751 164th Lane and the back of the drainage ditch to prevent stormwater runoff from draining onto this property.  The City Engineer indicated he would discuss this with the design engineer and would report back prior to requesting Council approval of a construction contract, which is currently anticipated to occur on September 22nd.
 
Below is a summary of the design options that were explored by Staff while preparing plans, as well as Staff’s findings and recommendations for each.
 
Option 1: Build berm north of 164^th Lane at back edge of ROW
This option would be to construct a berm at the back edge of the right-of-way (ROW) generally between the driveway and the high point in the ditch to the west. The controlling factors are the high point in the ditch approximately 40 feet west (875.1) and the edge of the driveway 25 feet to the east (875.6). The berm could be built up to an elevation of (875.1) at the ROW. The culvert under 164^th Lane and the culvert under the driveway are slightly filled in and below existing ground in the low area of (874.2).
 
Findings/Recommendations - In large storm events an area approximately 65-feet by 15-feet would fill with water to a depth of 0.9-feet (11-inches), and during spring thaws this is likely to freeze.  Either way, the potential would exist for runoff to overtop the berm and flow across the yard as it does today.  Water would also stand in the ditch for significant periods of time making it difficult for the property owner to mow the ditch.  Staff does not recommend this option.
 
Option 2: Re-grade the ditch on the north side of 164^th Lane, build berm on north side of 164^th Lane at the ROW
This option was the preferred option, however, when potholing Northern Natural Gas (NNG) pipes we only found 3 feet of cover existing. By law, 3 feet of cover is required over these pipes. To re-grade the ditch would require approximately 1-foot of cut at the more eastern of the two NNG pipes which cross the ditch.
 
Findings/Recommendations - Relocating NNG pipes is not a cost-effective option and is not recommended by Staff.
 
Option 3: Re-grade ditch south of 164^th Lane, build berm north of 164^th Lane within ROW, replace culvert under 5800 164^th Lane driveway, add culvert under 164^th Lane
This option is depicted in the attached plans and includes filling in the front of the swale at the back edge of the ROW north of 164^th Lane. The south invert of the existing 164^th culvert (874.5) is the controlling factor on the potential depth of water in the low area of the ditch in front of 5751 164^th Lane.  The depth is 0.3-feet or 4-inches.  
 
Findings/Recommendations – Since this design provides an alternate route for stormwater runoff and an additional 7-inches of storage in the low area of the ditch, the risk of runoff entering and flowing through the swale on the private property is greatly mitigated.  However, if runoff does overtop the ditch it will run through the existing swale in the yard since this project does not propose to fill that swale. This would not occur except during a very large storm event or during a significant snow melt event.  Staff recommends this option.  

Adopt Resolution #20-176 approving plans and authorizing Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project #19-17.