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RPBCWD Preliminary Review Comments_20220215 protect. manage. restore. 18681 Lake Drive East Chanhassen, MN 55317 952-607-6512 www.rpbcwd.org Memorandum To: Bob Generous, Senior Planner From: Scott Sobiech, Temporary Interim District Administrator Subject: Proposed 855 Pleasant View Road Subdivision Preliminary Plan Review by RPBCWD Date: February 15, 2022 This proposed redevelopment will need a Riley-Purgatory-Bluff Creek Watershed District (RPBCWD) permit prior to beginning construction activities. We appreciate the opportunity to provide preliminary comments on the project. The RPBCWD has been contacted by the project proponent and received a permit application on February 7, 2022. We offer the following summary of preliminary RPBCWD review comments for the proposed project in Chanhassen, MN. Additional comments will likely arise as part of RPBCWD’s official review. The RPBCWD permit application, rules and rule guidance are available for download on the RPBCWD website: http://www.rpbcwd.org/permits/. The following comments are based on the rules that would likely apply to this project and highlight the areas where revisions or additional information would be needed to meet the RPBCWD rules. These review comments do not constitute approval, a variance, or exemption from the rules. Therefore, this project will require permit approvals from the RPBCWD Board of Managers. Rule C: Erosion and Sediment Control Erosion and Sediment Control Permit (Rule C) is required from the RPBCWD because more than 50 cubic yards of earth will be placed, altered, or removed and/or more than 5,000 square feet of land-surface area will altered (Rule C, Section 2.1). Please see Rule C, Section 3 for the applicable criteria and notes that must be included with the erosion control aspects of the proposed project. The needed erosion control notes for inclusion on the plan sheets are available for download under supporting documents on the RPBCWD website: http://www.rpbcwd.org/permits/. The most overlooked notes are the placement of six inches of topsoil and decompaction to 1200kpas or less. Rule D: Wetland and Creek Buffer Because runoff from the site is tributary to an onsite wetland, the project must conform to the requirements set forth by the RPBCWD Rule D – Wetland and Creek Buffers. To conform to RPBCWD Rule D, the following revisions are needed before the application will be considered complete: 2 • Wetland with average and minimum buffer width consistent with the RPBCWD wetland value classification must be provided along all wetland downgradient for the land-disturbing activities. • The buffer markers must be placed at an interval of no more than 200 ft (Rule D, Subsection 3.4.c). • Please revise placement of buffer markers. • Provide a detail on the plans showing the buffer markers. • Buffer areas and maintenance requirements must be documented in a declaration recorded after review and approval by RPBCWD in accordance with Rule D, Subsection 3.4. Rule J: Stormwater Management A Stormwater Management Permit (Rule J) is required for this project because more than 5,000 square feet of land-surface area will be altered (Rule J, Section 2.1) based on the information provided by the City. Based on the information provided, it appears the project is a redevelopment of an existing lot of record when RPBCWD reinstituted their regulatory program the criteria in Rule J, Section 3 would apply to the entire parcel (ie all three lots). Comments provided below are preliminary and general in nature and the applicant should review the RPBCWD’s Stormwater Management Rule for full details on submittal requirements. The following criteria would apply. • An applicant for a permit under this rule must demonstrate, using a model utilizing the most recent applicable National Weather Service reference data (e.g., Atlas 14), that the implementation of its stormwater management plan will: o Limit peak runoff flow rates to that from existing conditions for the two-, 10- and 100- year frequency storm events using a nested 24-hour rainfall distribution, and a 100-year frequency, 10-day snowmelt event, for all points where stormwater discharge leaves the site;  A hydrologic model to simulate runoff rates for pre- and post-development conditions for the 2-, 10-, 100-year, and 10-day snowmelt frequency storm events using Atlas 14 precipitation depths with a nested rainfall distribution must be provided. Nested storm distributions are available for download at the RPBCWD website (www.rpbcwd.org/permits). An electronic copy of the model must be provided for review. • Provide for the abstraction onsite of 1.1 inches of runoff from the new and reconstructed impervious surface of the parcel. On site infiltration testing must be provided to determine the appropriate design infiltration rates. • Provide for at least sixty percent (60%) annual removal efficiency for total phosphorus, and at least ninety percent (90%) annual removal efficiency for total suspended solids from site runoff. o Any onsite abstraction of runoff may be included in demonstrating compliance with the total suspended solids and total phosphorus removal requirements. • No structure may be constructed or reconstructed such that its lowest floor elevation is less than 2 feet above the 100-year event flood elevation and no stormwater management system may be constructed or reconstructed in a manner that brings the low floor elevation of an adjacent structure into noncompliance with this standard. 3 • Because runoff from this site is tributary to onsite wetlands, the project must comply with the wetland protection criteria in Rule J, Subsection 3.10. The project will need to treat runoff requirement of 90 percent total suspended solids removal and 60 percent total phosphorus removal for the medium value wetlands and 90 percent total suspended solids removal and 75 percent total phosphorus removal for the high and exceptional value wetlands. • Provide a chloride management plan as required by Rule J, Subsection 3.8, including the designation of an individual authorized to implement the chloride plan or MPCA-certified salt applicator. A chloride management plan template is available on RPBCWD’s permitting website under supporting documents (http://rpbcwd.org/application/files/8415/5594/6065/Chloride_Management_Plan_Template_12Ap ril2019.pdf). If the roadways will be transfer to public ownership or right of way, please provided documentation demonstrating that. This information does not need to be provided prior to making a recommendation to the RPBCWD Board. • Applicant must provide a maintenance and inspection declaration. A maintenance declaration template is available on the permits page of the RPBCWD website (http://www.rpbcwd.org/permits/). Summary Based on the information provided to date, the proposed design does not meet the RPBCWD rules and a permit from the RPBCWD will be required prior to construction to likely cover the following: Erosion and Sediment Control, Wetland and Creek Buffers, and Stormwater Management. The online permit application, rules, maintenance declaration template, and financial assurance templates are available for download on the RPBCWD website: http://www.rpbcwd.org/permits/. Please contact us with any questions.