Resolution_PFacilitiesAgmt2022_City of Roslyn

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Pavemerd sur'aco F o•.v spreader (gravel) -\ - Flmi surp S' mm taaspd 7•S <slcpas ISN JZ Section A -A Cslleetorcm h (typ.) FiGuRE 2. VErETA-!E;) F!i.TER STRir Various factors were considered in identifying feasible locations for the biofiltration swales. It is preferred to locate biofiltration swales adjacent to paved roads and within the public right-of-way. To be considerate of the historical context of the City, buildings contributing to the historical district were added to the inventory of data. Biofiltration facilities were located away from these buildings to the maximum extent feasible. Where a location is ideal due to site topography, proximity to existing storm sewer and estimated runoff from the water quality storm, biofiltration facilities may be located adjacent to those historical buildings to maximize stormwater treatment benefit (such as on East Washington Avenue). Biofiltration facilities were also located at least 300 feet from wetlands according to City Policy H2.5. Lastly, biofiltration swales were prioritized in subbasins that were 1.5 acres or larger and produced at least 0.1 cubic feet per second of runoff during the water quality storm event. These subbasins are presented as High Priority for Treatment Subbesins in Exhibit 3. The various site constraints and locations of the proposed biofiltration sweles are shown on Exhibit 3. Within the CIP 1 Treatment Assessment Area, biofiltration swales are proposed along North First Street, North A Street, East Washington Avenue, and East Pennsylvania Avenue. Within the remainder of the Treatment Assessment Area, biofiltration swales are proposed along North Sixth Street, West Third Street, Second Street, South First Street, and portions of West Nevada Avenue, West Utah Avenue, West Arizona Avenue, Dakota Avenue, and West Montana Avenue. These biofiltration swales will be shallow and will have overflow risers as well as underdrains that will connect into the existing storm sewer network. For the unsewered areas of the City south of California Avenue, vegetated lifter strips may be located adjacent to roadways where compatible with street slopes and adjacent land uses. These would provide runoff treatment benefits that have not yet been quantified or mapped with this study. This is a general recommendation for this area of town or other parts of the City where biofiltration is deemed not viable.