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HomeMy WebLinkAboutSP-22-014 - Supplemental - 0033 Andrews Avenue Memo To: South Burlington Development Review Board From: Christine Gingras, Public Works Project Manager CC: Marla Keene, Development Review Planner Date: March 8, 2022 Re: City of South Burlington Site Plan Application for Develop Review The City of South Burlington Stormwater Utility is working with Stonehedge South Area Association to redevelop an approximately 320’ long swale. The first 250 feet of the swale is located on the Association’s property, while the last 71 FT of swale is located in Szymanski Park, owned by the City of South Burlington. In 2017, the City assisted the Homeowners Associations (HOAs) within the Stonehedge development to address stormwater issues associated with an expired State of Vermont stormwater permit. In addition to constructing new bio-retention areas and drainage infrastructure improvements in the neighborhood, a new stormwater detention pond was constructed in Szymanski Park with the intent to utilize an existing drainage swale between K and L clusters. The original swale was constructed at the time the condominiums were built (See 1983 Site and Utilities Plan for Stonehedge Condos Cluster L PDF). Since then, sediment deposition and growth of a thick root mat of giant reed have clogged the historic channel. Flow out of the neighborhood is currently impeded, resulting in flooding and safety (ice related) issues for residents in the L cluster. The City is proposing to restore positive drainage within the swale by performing maintenance to clear out accumulated material. As vegetation has grown up within this swale area, the City is proposing to rework the swale around mature trees. The proposed work would allow the swale to drain 6.9 acres of impervious surface from a total 34.9 acre drainage area located to the north of the proposed swale. Straddling two parcels, 78% of the project is on Stonehedge South Area Association property. The other 22% of the project is on the Szymanski Park parcel, owned by the City of South Burlington. The proposed project will have no impact on current uses, buildings, or impervious areas. Construction activities (project wide) will have the following impacts on class II wetlands: 8,115 SF of permanent ("other," non-fill) impact to wetland, 4968 SF of temporary impact to wetland, 440 SF of permanent impact to buffer (excavation/non-fill) and 1453 SF of temporary impact to buffer. On the City’s parcel, the proposed project will permanently impact 1,785 SF of existing class II wetland and 97 SF of associated buffer. Wetland impacts are from excavation activity. Tracked equipment will access the project from Stonehedge Drive in order to avoid impacts in Szymanski Park for site access. Required excavation and removal of approximately 72 yards of fill on the Szymanski parcel is estimated. This material will be hauled offsite. Impacts to wetland and buffer are required in order to restore the historic flow pattern, allowing stormwater from the culverts outleting on the south side of Stonehedge Drive to drain to the stormwater treatment pond below. Avoidance of wetland impacts to construct the swale is not feasible, since the problem is localized to the area between the culvert outlets and the stormwater pond below. Alignment of the proposed swale was selected to minimize impacts on existing trees/plants to the greatest extent possible. As avoidance could not be achieved for the project, the minimization criteria was utilized instead. The proposed swale is the minimum size necessary to restore positive drainage, with an average cross-sectional depth of 1 foot. Restoration of the wetland will be accomplished by the planting of a wetland seed mix over the disturbed area, and the swale is expected to return to a functioning wetland as the vegetation establishes. The State of Vermont Department of Environmental Conservation and Army Core of Engineers have both issued permits for this project. We are submitting this project to the South Burlington DRB for review as a site plan application due to the proposed class II wetland impacts and the amount of fill that will be removed and relocated on site. Included with this application, please find final project plans, a copy of the ACOE wetland permit, VT ANR wetland permit, 1983 Site and Utilities Plan for Stonehedge Condos Cluster L, 2018 Record Drawings for the stormwater treatment pond in Szymanski Park, and Szymanski Park abutters. If you have any questions, please contact me at (802) 658 -7961 x 6111 or cgingras@southburlingtonvt.gov.