10-12-2022 Council Packet - Laserfiche WebLink

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Prepared by: Bolton & Menk, Inc. Proposed Improvements Twin Lake Boulevard ǀ 0N1.125376 Page 8 in the need for a retaining wall near the western intersection of Twin Lake Boulevard with Vadnais Boulevard. There are existing steep slopes east of Bankers Drive along the Five Star Estates property. Although the roadway is being narrowed in this location, the establishment of a trail will push the top of the embankment out 5’-7’. The existing embankment is already graded at a 2:1 slope. Final trail design will need to accommodate re-grading and armoring of this embankment. Armoring may include a combination of erosion control blanket, turf reinforcement mat, and vegetation. A temporary easement may be required to perform this grading outside of the existing right-of-way. The trail alignment along the proposed multi-family development sites is proposed to be located near an existing drainage ditch. This area is outside of the right-of-way and in an area that is heavily wooded. Property owners in the area have been vocal advocates of keeping as much natural vegetation screening as possible along the developments. Construction of a trail along these development sites will inevitably require tree and brush clearing to accommodate construction. However, project staff will work during final design to select an alignment that minimizes the loss of mature and significant trees to the extent possible. Additionally, new trees and vegetation will be planted after trail construction. In other areas where the trail alignment is proposed through heavy vegetation, a trail corridor will be cleared to allow for long-term maintenance and useability of the trail. Additionally, selective clearing is proposed between the roadway and trail to allow visibility for trail users. Significant or mature species would be left in place during the selective clearing. STORMWATER MANAGEMENT The proposed roadway improvements alone do not trigger permanent stormwater management improvements through either the Ramsey-Washington Metro Watershed District (MWMWD) nor the Minnesota Pollution Control Agency (MPCA). However, grading and new impervious surface associated of the bituminous trail installation along the roadway will trigger permanent stormwater management. • Rate Control o Runoff rates for the proposed project shall not exceed existing runoff rates for the 2-yr, 10-yr, and 100-yr critical storm events using Atlas 14 precipitation depths and MSE III storm distributions, or as approved by the district. Runoff rates may be restricted to less than the existing rates when the capacity of downstream conveyance systems is limited • Volume Control o Stormwater runoff shall be retained onsite in the amount equivalent to 1.1 inches of runoff over the new and reconstructed impervious surfaces of the development.” • Water Quality o The project shall incorporate effective non-point source pollution reduction BMPs to achieve 90% total suspended Solids (TSS) removal from the disturbed area of the project on an annual basis. Permanent stormwater management facilities will be incorporated into final design and implemented with the project. These improvements will likely include infiltration/filtration basins, ditch checks, and water quality manholes. No work can begin prior to receiving a permit with the Ramsey-Washington Metro Watershed District.