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HomeMy WebLinkAboutSD-24-11 - Supplemental - 0252 Autumn Hill Road (13)The Stormwater Section has reviewed the “Bolduc Parcel” site plan prepared by O’Leary-Burke Civil Associates, dated 5/24/24 and last updated on 6/3/24. We would like to offer the following comments: 1. This project is located in the Muddy Brook watershed. 2. As the project proposes to increase impervious onsite to more than one-half acre of impervious surface, the project is subject to the requirements of section 13.05 of the LDRs. 3. The following application requirements listed in 13.05(C) are missing and should be provided: a. A plan showing the drainage area being captured by the proposed stormwater treatment practice, as well as soil types/hydrologic soil groups b. A brief written description of the proposed stormwater treatment 4. The provided HydroCAD modelling does not include the 25-year storm. Please provide this analysis in accordance with Section 13.05(C)(6) of the LDRs. 5. The HydroCAD model shows stormwater exiting the gravel wetland through the 1-yr orifice during the WQv storm, thus not meeting the WQv standard for extended detention. 6. The pipe invert out of the outlet structure of the gravel wetland is at 359.0. This means that the permanent pool will be at 359.0 and that the wetland soil will be entirely saturated. Is it possible to lower the invert of the pipe out of the outlet structure? 7. Per the Vermont Stormwater Management Manual, pretreatment swales with a slope greater than 5% must utilize check dams. Please include a check dam at the curve of the proposed drive, where the slope is greater than 5%. 8. Please confirm the separation distance of each of the sewer/stormwater pipe crossings. 9. Is the proposed gravel wetland sized such that it will be capable of treating any proposed impervious on Lot 1? 10. How will any residence constructed on Lot 1 connect to the access from Windswept Ln? The site plan shows the proposed pretreatment swale running along the entirety of the western portion of the proposed driveway. Will the pretreatment swale be shortened when the home for Lot 1 is constructed? 11. What is the elevation of the proposed 12-ft drive over the 18” culvert? 12. It is recommended that the outlet of the proposed 18” culvert be altered such that it does not discharge onto the adjacent lot. The current configuration would cause runoff from approximately 5.5 acres of land to be channelized and discharged directly onto the adjacent lot, which is likely to cause erosion. 13. Is any inlet protection proposed for the yard drain within the pretreatment swale? 14. What will be the phasing of construction? 15. Will the proposed single-family home and ADU be guttered? 16. The DRB should include a condition requiring the applicant to regularly maintain all stormwater treatment and conveyance infrastructure.