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HomeMy WebLinkAboutPeer Review 1.19.23 January 19, 2023 Ms. Brittany DiRienzo, Conservation Administrator Town of Yarmouth Yarmouth Town Hall 1146 Route 28 South Yarmouth, MA 02664 Re: Yarmouth Riverwalk Park, Route 28 Technical Stormwater Peer Review 669 Route 28 West Yarmouth, MA 02673 TRC Project No. 526741 Dear Ms. DiRienzo, TRC has completed a technical stormwater peer review of the Stormwater Management Permit Application prepared by Beta Inc submitted to the Commission on November 17, 2022 and provided to TRC on December 2, 2022. The goal of the review was to determine if the application is technically complete and to evaluate general compliance with the Yarmouth Stormwater Management Regulations, effective July 1, 2021. The following PDF documents prepared by Beta, Inc were reviewed: 1. Stormwater Management Report, dated November 17, 2022. 2. Town of Yarmouth Stormwater Management Permit Application, dated November 17, 2022. TRC’s observations are provided below, following the applicable standard in italics. TRC has determined that the application is neither complete nor in compliance with the Stormwater Management Regulations as summarized below. Revised documents and a detailed response to the following comments should be provided for further review. Yarmouth Conservation Commission Stormwater Management Regulations Waiver Request The applicant requests “two waivers… from the by-law” in Section 7.1 of the Stormwater Management Report. However, the two specific standards for which the waiver is requested are not stated. At least one of the standards appears to be 2.05(4), which requires stormwater treatment. 1. Each standard for which a waiver is requested should be listed and addressed. 2. The location of Isolated Vegetated Wetland (IVW) 2 should be clarified and identified on the plans. It appears that the area labeled “Wetland Area 3” on the plans is described as IVW 2 in the report. 3. Details of the “stabilized aggregate walkway” and “reinforced turf” have not been provided in the plans nor described in the report. It is not clear if these material meet the definition of impervious surface that would require treatment. Details of both should be included in the plans and the anticipated perviousness of each should be described in the report. 4. Standard 2.05(4)(d), allowing for offsite mitigation, should be addressed in the waiver request. 2.04(1) Stormwater Management Site Plan (k) Estimated seasonal high groundwater elevation using the Cape Cod Commission adjustment method (Cape Cod Commission Technical Bulletin 92- 001, as amended) in areas to be used for stormwater retention, detention, or infiltration; 1. While test pit locations are indicated on the existing conditions plans and estimated seasonal high groundwater calculations are included in Section 5 of the report, test pit logs have not been provided. The logs should be provided for review. (l) The existing and proposed vegetation and ground surfaces with runoff coefficient for each; 1. The ground covers and associated runoff coefficients should be shown on the Drainage Area Plans. (m) A drainage area map showing pre- and post-construction watershed boundaries, drainage areas, and stormwater flow paths; 1. Drainage areas delineated on the south side of the site are only partially shown. The delineated drainage areas should be shown in their entireties. 2. The pre-construction drainage area POA 1 “Woodland Beyond Drive-in Area” flow path should be provided. 3. Discrepancies between the drainage areas shown on the proposed conditions drainage area map and the areas presented in Appendix F – Watershed Data and Appendix H – Proposed Conditions Calculation should be corrected. The area listed in POA 1 “Infiltration System 1” area does not match the areas listed in Appendices F and H. The drainage area to the artists’ shanties are not depicted in the drainage area map. The "woodland outside riverpark” and "IVW 2” drainage areas described in Appendices F and H are not depicted in the proposed conditions drainage area map. 4. Proposed conditions stormwater flow paths are not provided. However, this is not a significant omission as the minimum time of concentration (6 min) is assumed. 5. Flow direction arrows should be added to all flow path for clarity. (n) A description and drawings of all components of the proposed drainage system including: i. locations, cross sections, and profiles of all brooks, streams, drainage swales and their method of stabilization; ii. all measures for the detention, retention, and/or infiltration of stormwater; iii. all measures for the protection of water quality; iv. the structural details for all components of the proposed drainage systems and stormwater management facilities; v. notes on drawings specifying materials to be used, construction specifications, and typical details and cross- sections; and, vi. proposed hydrology with supporting calculations. 1. The report describes a “drip edge” along the roof line of the artist shanties. The location and associated details should be provided in the design plans. 2. The horizontal separation between the restroom building and the Stormtech infiltration chamber should be indicated on the plans to demonstrate that the minimum setback requirements are met. 3. Inverts and inlets of Infiltration System 2 should be labeled in plan view. 4. The check dam cross section detail refers to the plan view for the location but is not labeled on the grading and drainage plan. The check dam locations should be labeled on the plans. 5. Both infield trenches are labeled as “Prop. Infield Trench No 2” on the Grading and Drainage plan. The labels should be corrected. 6. The “Infiltration System No. 1” detail indicates pavement removal beneath the proposed system. The material to replace the removed pavement and methods for restoring the infiltration rate of compacted subsoils should be specified. 7. Edge infiltration trenches should be labeled on the grading and drainage plans. 8. Details for porous pavement, cross sections for the infiltration basins, stabilized aggregate surfaces, and reinforced turf should be provided. 9. The vertical separation between the estimated seasonal high groundwater table and the inverts of all infiltration BMPs should be indicated on the details. 10. The Outlet Control Structure at Infiltration Basins detail elevations do not match the elevations listed in plan view for either basin 1 or 3 for top elevation or spillway crest. The details or plan view callouts should be revised accordingly. (p) Timing, schedules, and sequence of development including clearing, stripping, rough grading, construction, final grading, and vegetative stabilization; 1. The sequence of development timing/schedules should be provided. (r) Calculations supporting the design of the stormwater management system and its compliance with the performance standards established in these regulations; 1. The proposed conditions HydroCAD model of Pond 1P should include the outflow through the Outlet Control Structure. Additionally, the bottom elevation of the pond in the HydroCAD model does not match that of plan view. Either the model or plan view should be updated accordingly. 2. The number of chambers per row indicated on the detail for Infiltration System 2 does not match the number of chambers listed in the HydroCAD model. This discrepancy should be corrected. 3. The crest elevation for Outlet Control Structure 2 indicated on the design plan does not match the elevation listed in HydroCAD. The top of Infiltration Basin 3 indicated on the design plan does not match the elevation listed in HydroCAD. Either the plans or the model should be updated accordingly. 2.05 Stormwater Management Performance Standards (2) Good housekeeping procedures shall be used to reduce sources of sediment, phosphorus, nitrogen and other contaminants in stormwater runoff. These shall be documented in the Operation and Maintenance Plan and must include… 1. The good housekeeping measures described by the Yarmouth Stormwater Regulations should be provided in the Operation and Maintenance Plan. 2.06(4) Erosion and Sediment Control Plan (4) Erosion and Sediment Control Plan Content… 1. The “Existing Conditions and Site Preparation Plan – 1” appears to be presented as the Erosion and Sediment Control Plan. While erosion control measures are shown on this drawing it does not include items such as a Limit of Disturbance for Phase II work, contours, inlet protection, or methods of protecting infiltration areas during construction. While details of several erosion control barriers are provided on sheet C.7.7, the locations are not labeled on the drawing. The plans should be revised to provide additional details and more robust erosion control measures. Details of all proposed erosion control measures, such as temporary sediment basin and inlet protection devises, should be provided. 2.07(1) Operation and Maintenance Plan (post-construction) (c) The person(s) responsible for financing maintenance and emergency repairs; 1. The operation and maintenance plan states that “The system inspection and maintenance will be included within the annual budget of the Town of Yarmouth Department of Public Works and should be implemented as part of their normal routine for maintenance of the stormwater BMPs in town,” but does not include discussion of financing of emergency repairs. (g) The signature(s) of the owner(s); 1. The copy provided has not been signed. General Technical Review The following general technical review comments should be addressed in addition to the technical regulatory review comments provided above. 1. The Limits of Disturbance should be shown on all proposed conditions sheets. Findings Based on these observations, TRC concludes that the application is not in compliance with the Stormwater Management Regulations. Additional calculations, drawings, and documentation should be provided to demonstrate compliance as described above. A detailed response to the review comments should be provided along with a reference to the associated revision or supporting material. Sincerely, TRC Jason M. Gold, P.E. Manager, Civil/Site Engineering Services