Agenda - Public Works Committee - 06/16/2015

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Public Works Committee 5. 2. Meeting Date: 06/16/2015 By: Bruce Westby, Engineering/Public Works Title: Consider Recommendation for Zeolite Street Storm Sewer Extension to Lake Ramsey Purpose/Background: Purpose: The purpose of this case is to consider providing a recommendation to the City Council for extending the existing storm sewer that runs along the west side of Zeolite Street to Lake Ramsey in 2015. Background: During development of Ramsey Town Center, 73" Arch Reinforced Concrete Pipe (A -RCP) storm sewer was installed along the west side of Zeolite Street for the purpose of providing drainage from the Ramsey Town Center 8th, 9th, and IOth Additions, and to allow for future drainage of a portion of the developed/undeveloped areas to the north. At the time the storm sewer was installed it was terminated just past the outside edge of the shoulder along the south side of Bunker Lake Boulevard, west of Zeolite Street. The end of the storm sewer pipe was covered with a sheet of plywood before being backfilled. This plywood sheet rotted and failed in 2012, at which time it was replaced with another sheet of plywood as the expectation was that the line would be extended later that year, which then never occurred. This existing storm sewer line incorporates an outlet pipe from the triangular parcel of RTC 8th Addition in the northwest corner of the intersection. Therefore, if the pipe fills with stormwater to a certain point the water can then flow out of the pipe and into the triangular parcel where it is then stored until it can infiltrate into the ground. However, the pipe always has some standing water in it (approximately a foot) so the sheet of plywood is continually wet. Staff therefore recommends removing the plywood and extending the storm sewer to Lake Ramsey as originally intended this year to prevent the plywood from failing, in which case a portion of the pavement along Bunker Lake Boulevard could potentially fail. It is important to note that at the time the storm sewer was terminated it was discussed whether the pipe could or should be downsized by approximately half its diameter from the end of the existing pipe into Lake Ramsey, primarily to save on construction costs. If this were to occur it would remove any ability for this storm sewer to provide future drainage for the area north of RTC tali Addition. Staff does not support downsizing the pipe for two reasons. First, it is poor practice to reduce pipe size as you proceed downstream, especially if the pipe is downsized significantly as was previously discussed. Second, reducing the pipe size would reduce or eliminate flexibility for developing the area to the north. The estimated cost savings associated with reducing the pipe size would be less than $50,000. Timeframe: Approximately 10 minutes for presentation and discussion. Observations/Alternatives: Staff has developed a draft set of plans and a preliminary cost estimate for the proposed improvements. Attached are four of the draft plan sheets showing the proposed improvements and detour route. This work will include the lowering of an existing 12" watermain line, and the removal and replacement of pavement areas along Zeolite Street and Bunker Lake Boulevard. Detouring is proposed to be routed along Center Street during the week or two it would take to construct the improvements and repave the roads.