1A, US 10CR 96 Grade Separation & CSAH 96 Improvements - Project Update

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City of Arden Hills August 5, 2009 Page 2 of 3 Use of either the 10' or 20' noise wall would result in less than a 3 decibel noise reduction, a change that would not be recognized by the average human ear. Earthen Berm - An earthen berm was evaluated south of Royal Hills Park in the immediate vicinity of the Snelling A venuelBriarknoll Drive intersection. The berm would build off of the existing sledding hill in the park and extend approximately 600' to the south. The berm height would vary in height from approximately 12' at the park to 8' south of Briarknoll A venue. Figure 2 illustrates the grading limits and approximate elevation of the berm. An area of approximately] .8 acres would be impacted by the berm construction. Grading for the berm would require approximately 18,000 cubic yards of fill. Excess material from the TH 10/CSAH 96 Grade Separation project may be suitable for berm construction and could be acquired for little or no additional costs if completed as part of the county's project. Additional costs associated with the berm would include site clearing and preparation, turf establishment, and landscaping. Due to the heavy tree cover presently on site, tree replacement would be necessary. While trees generally do not provide noise mitigation~ they do add visual screening and improve livability of neighborhoods adjacent to highways. At a minimum, 32 coniferous trees would be proposed at or near the top of the berm in two rows spaced at 25' apart. In addition, 10 deciduous trees would be proposed along Snelling Avenue. Transplanting of existing trees may be an option, but would require moving trees twice and may not provide substantial cost savings. The estimated costs associated with the berm are provided below: Item Unit Quantity Total Cost Site Clearing and Prep. $4000/acre 1.8 acres $7,200 Common Borrow $8/cubic yard ] 8,000 cy $144,000 Turf Establishment $720/acre ] .8 acres $1 ,300 Tree $300/tree 42 trees $12,600 Total Estimated Cost of Berm $165,100 Privacy Fence - In addition to the earthen berm, a 6' privacy fence could be considered in Royal Hills Park to provide screening to areas not adjacent to the berm. The wooden fence would enhance the park setting while providing visual screening of the highway for park users and adjacent residences. An estimated 400' long fence could be constructed along the western boundary of the park. With an estimated unit cost of $60/1inear foot, the estimated cost of the privacy fence is: 6' Privacy Fence = $24,000. Findings and Recommendations Mitigation of noise in the Briarknoll neighborhood may be difficult to achieve. Since existing and future noise levels do not meet state and federal thresholds, any noise mitigation would be at the cost of the City of Arden Hills. The earthen berm alternative may be an effective means of addressing noise concerns in the neighborhood at a relatively low cost. If completed with the TH ] O/CSAH 96 project, the cost to the City could be as low as $25,000 to $50,000. While the berm and associated tree placement would provide excellent visual screening of the highway for the neighborhood, it would not provide noticeable reductions in noise. The berm would result in a similar reduction in noise as the 10' noise wall of 3 decibels, a change that would not be recognized by the average human ear. Input from the neighborhood is recommended prior to moving forward with a more formal feasibility study. DESIGNING FOR A BETTER TOMORROW