Agenda - Council - 09/22/2020 - Laserfiche WebLink

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fill with water to a depth of 0.9-feet (11-inches) and runoff could still overtop the berm and flow through the yard. During spring thaws this water is likely to freeze. Staff does not recommended this option. Option 2: Re -grade ditch and build berm within ROW north of 164th Lane This was the preferred option, however, after potholing the two Northern Natural Gas (NNG) pipes only 3 feet of cover was observed. By law, a minimum of 3 feet of cover is required over these pipes. To re -grade the ditch would require approximately 1-foot of cut over the eastern NNG pipe resulting in 2 feet of cover, which by law is not enough cover and would require the pipe(s) to be lowered or relocated. Findings/Recommendations — Lowering/relocating NNG pipes would not be cost-effective. Staff does not recommended this option. Option 3: Re -grade ditch south of 164th Lane, build berm within ROW north of 164th Lane, replace driveway culvert at 5800 164th Lane, and add culvert under 164th Lane This option is depicted in the attached plans and includes filling in the mouth of the swale at the back edge of ROW north of 164th Lane. The south invert of the existing 164th Lane culvert (874.5) will control the depth of water standing in the lowest area of the ditch west of the driveway at 5751 164th Lane. The standing water depth will therefore be 0.3-feet or 4-inches, which will disappear in less than 2 days due to evaporation and infiltration allowing the ditch to be regularly maintained. Findings/Recommendations — This design directs all stormwater runoff south of 164th Lane through the re -graded ditches and new culvert under 164th Lane to the existing drainage easement and swale along the west property line of 5751 164th Lane. The ditch north of 164th Lane will now only receive runoff from one lane of 164th Lane, and given there is 7-inches of storage in the low area of the ditch, the risk of runoff entering the swale that runs across the private property is negligible. However, if runoff does overtop the ditch it will run through the existing swale in the yard since this project only proposes to fill the mouth of the swale, though this would only occur during very large rain events or a significant snow melt event. The swale would therefore act as an emergency overflow only. Staff recommends this option. On September 15, 2020, the Public Works Committee reviewed the quote submitted by Dryden Excavating, Inc. and unanimously recommended that the City Council accept the quote and award a construction contract to Dryden Excavating, Inc. in the amount of $22,827.78 for 5751 164th Lane Drainage Improvements, Improvement Project #19-17, and to authorize Bolton & Menk to stake construction at a cost not -to -exceed $1,000. Action: Adopt Resolution #20-214 accepting the quote of and awarding a construction contract to Dryden Excavating, Inc. in the amount of $22,827.78 for 5751 164th Lane Drainage Improvements, Improvement Project #19-17, and authorizing Bolton & Menk to stake construction at a cost not -to -exceed $750. Resolution 20-214 Plans RFQ BMI Staking Proposal Attachments Form Review Inbox Reviewed By Date Kurt Ulrich Kurt Ulrich 09/17/2020 03:14 PM