HomeMy WebLinkAboutSD-20-35 - Supplemental - 0570 Shelburne Road (20)The Stormwater Section has reviewed the Preliminary & Final Subdivision Plat for Chase- Proposed Chase Building with Remote Drive-Up ATM prepared by Stonefield Engineering and Design,
dated September 18, 2020. We would like to offer the following comments:
This project is located in the Potash Brook watershed. The watershed is listed as stormwater impaired by the State of Vermont Department of Environmental Conservation (DEC). Potash Brook
is listed as a warm water fish habitat according to Vermont Water Quality Standards, Environmental Protection Rule Chapter 29A (incorrectly classified as Cold-water on page 2, Section
2.4 of applicant’s report).
The redeveloped site is larger than a ½ acre which requires the applicant to comply with Article 12.03 of the LDRs.
Section 5.3 of the report speaks to the proposed Tier I STP, yet the soil analysis describes a soil group D. Can the applicant demonstrate that the site provides an infiltration rate
of at least 0.2 inches/ hour? Soil borings and infiltration tests are required in the location of the proposed STPs. Please refer to the 2017 Vermont Stormwater Management Manual (VSMM)
4.3.3.2 for guidance.
The applicant needs to demonstrate treatment of the redevelopment area in accordance with Section 2.4 VSMM by treating 50% of the redevelopment area and reducing existing impervious
surface area by 25%, or a combination thereof as described in that section. Report notes that it will be decreased by 3,015 SF which is only a 10% reduction.
Applicant is requested to include all sections and details pertaining to the two Bioretention systems. The north arrows in the Stormwater Report don’t align with those in the planset.
Does B-2 have an overflow or outlet structure? Clearly show all curb cuts and overflows with detail. Included specification for bioretention soil. Please check spacing of plantings
within the Bioretention areas. Shrubs and trees appear to be closer than recommended. Is there any reason the plan cannot be drawn at a larger scale?
If runoff is delivered to the bioretention practice via a stormpipe, the STP shall be designed offline. Is a flow splitter being proposed? What is acting as a forebay for the Bioretention
practice? Please reference the VSMM for guidance.
From plan sheet C-7 Stormwater Management Plan, it appears that flow is being delivered to B-1 at the same elevation that the yard inlet will discharge flow at, which would cause the
B-1 system to be bypassed. Further detail is necessary.
Please include all stormwater related features on Site Plan Sheet C-5.
The applicant is required to submit a Maintenance Plan for all stormwater treatment practices as outlined in LDRs Article 12.03.D(e). It is recommended that the DRB include a condition
requiring the applicant to regularly maintain all stormwater treatment and conveyance infrastructure.
Were methods considered for treating the impervious surfaces on site that will not be treated?
Proposed soil stockpile location will limit access to southern portion of site (including construction of bioretention beds).