Agenda Packets - 2003/11/03 - Laserfiche WebLink

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________________________________________________________________ To: Mounds View City Council From: Greg Lee CC: Kurt Ulrich Tom Field – 8409 Knollwood Drive Date: 10/03/2003 Re: Storm Sewer Manhole cover at 8409 Knollwood Drive During the Public Input section of the City Council Meeting on August 25, 2003, Mr. Tom Field made a request of the City Council. Mr. Field requested that a storm sewer manhole cover that has been below grade for the last several years to be re-buried. This manhole cover is located directly behind the curb within the boulevard in front of Mr. Field’s property at 8409 Knollwood Drive. At the time of the meeting, the Public Works Director had no knowledge of this issue. The City Council then directed the Public Works Director to look into this issue and report back. The findings of the research are below: As part of the new storm sewer cleaning, inspection, and maintenance program a storm sewer manhole was located in the boulevard adjacent to 8409 Knollwood Drive. This manhole was unburied and access was restored to allow for storm sewer cleaning and inspection activities. Upon completion of these activities, the adjacent property owner, Mr. Field, requested that the manhole be reburied. The Public Works Foreman informed Mr. Field as to the reasons why this manhole cover needs to be accessible and brought up to grade. Mr. Field informed the Public Works Foreman that several years ago the City’s Public Works Director gave direction to bury the manhole cover. Upon investigation, this manhole is located at the intersection of a 21-inch storm sewer pipe intersecting with a 30-inch pipe. The 21-inch pipe conveys storm water for all of northwestern Mounds View. Attached is a map of the City storm sewer system. This manhole is a critical, high volume, “T” intersection. Storm sewers are most susceptible to failure during a large storm event or during the spring snowmelt and possible resulting blockage. For the spring snowmelt, this blockage typically consists of leaves and debris from the preceding fall. During the spring snowmelt the melt water will wash debris into the storm sewer system. When the spring snow melt occurs the ground is typically frozen, making access to a buried manhole extremely difficult. The pipes entering and exiting the manhole are at minimal flat grades and create a “T” intersection where the storm water must make a 90-degree turn. Although there has not been an incident with this manhole in recent history, this represents a point where the sewer could likely fail.