Agenda - Council - 11/12/2013 - Laserfiche WebLink

Home

CC Regular Session 7. 4. Meeting Date: 11/12/2013 By: Bruce Westby, Engineering/Public Works Information Title: Consideration of Alternatives for Replacing Vanadium Street Culvert Purpose/Background: Purpose - The purpose of this case it to evaluate options for replacing the existing 48" Corrugated Metal Pipe (CMP) culvert that conveys storm water runoff flowing through Anoka County Ditch #14 under Vanadium Street, north of Green Valley Road. This culvert, which is approximately 40 years old, is failing due to severe corrosion and should be replaced as soon as practical to prevent it from collapsing, resulting in the subsequent collapse of a portion of Vanadium Street. Figure 1 (attached) includes two pictures showing the existing corrosion. Background - The city completed a storm sewer maintenance project this fall along Vanadium Street, north of Green Valley Road. Figure 2 (attached) shows the project location, and Figure 3 (attached) shows where the culvert crossing is. This project consisted of extending and/or replacing various culverts and establishing new turf in the impacted areas within the roadside ditches along Vanadium Street. The project was awarded to Dryden Excavating, who submitted a low quote of $8,630. Final project costs came in at $10,850. This storm sewer maintenance project was not identified in the City's 5-year CIP. During this maintenance project, the property owner at 17730 Vanadium Street NW notified staff that a sink hole was forming in their back yard, and that the slope in their back yard along Anoka County Ditch #14 has been eroding more and more over the last several years. Upon reviewing their concerns, staff noted that the sink hole was forming around a culvert apron that collects runoff from the ditch along the west side of Vanadium Street and directs it into County Ditch #14. Staff also noticed that the erosion issues in the back yard were due in large part to the existence of a bend in the County Ditch, which appeared to be created by the 48" culvert under Vanadium Street being installed at an angle to the natural ditch line. Upon checking the condition of the 48" CMP culvert under Vanadium Street, staff found it to be in poor condition with extensive corrosion, particularly along the spring -line of the pipe as shown in Figure 1. When the culvert is replaced, staff plans to realign the culvert by moving the inlet end on the west side of Vanadium Street to the north about 10 feet which will straighten the ditch line out to minimize the potential for future erosion of the ditch bank. Since this culvert conveys runoff through County Ditch # 14, staff contacted Anoka County to inquire what the County's requirements are for replacing such culverts. Staff was directed to replace the culvert with a new culvert of the same material and size, and to install it at the same elevations to ensure the drainage capacity of the culvert, and therefore the ditch, remains unchanged. Staff was also informed that if a different culvert material was to be proposed the city would need to first complete storm water modeling to determine the effects of the new culvert on flows in the ditch, both upstream and downstream. Based on the County's response, and considering the time of the year, staff immediately requested quotes from three local contractors for replacing the culvert with a new 48" CMP culvert. Quotes ranged from $33,655 to $50,184 and covered all costs for removing the old culvert, trenching the new culvert across the road one half at a time to allow one lane of traffic to remain open at all times, for establishing turf on all disturbed areas, and for repairing/paving Vanadium Street. It is important to note that one lane of traffic must remain open at all times since there is no other access to the properties north of this culvert so everyone must use Vanadium Street and Green Valley Road for access.