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Mr. Michael Grochala May 23, 2025 Page 3 Local Stormwater Management Requirements Stormwater management within the future development of the study area must be in conformance with local requirements of the City of Lino Lakes, RCWD, and MPCA. Some requirements are more stringent than others. However, the development in the study area will need to demonstrate that all local standards are being met under proposed stormwater management techniques. The following is a summary of major stormwater management requirements: • Rice Creek Watershed District The RCWD rules (approved November 13, 2024) require that proposed peak runoff rates shall not exceed existing for the 2, 10, 100-year 24-hour rainfall events. Proposed projects must not adversely affect off-site water levels or resources supported by local recharge, or increase potential for on- and off-site flooding, during or after construction. The RCWD requires a water quality treatment volume depending on the area of new or reconstructed impervious surface. Applicants can use BMPs including infiltration, water reuse, filtration, and stormwater ponds to achieve the required water quality treatment volume. Each BMP design variation has a different pollutant removal factor, and applicants must provide sufficient treatment volume depending on the BMP used for the site. The RCWD has an approved Comprehensive Stormwater Management Plan (CSMP)for a portion of the AUAR area (Northeast Lino Lakes Drainage Area CSMP). This purpose of the CSMP is to present an alternative means to meet the RCWD rules. Projects within the CSMP area must conform to design requirements detailed in the CSMP report as applicable. • City of Lino Lakes The City's Stormwater, Erosion, and Sediment Control Ordinance (adopted October 26, 2015; amended January 9, 2023) requires proposed development to maintain or decrease runoff volume and flow frequency, duration and peak runoff rates. Proposed development must also increase infiltration or filtration opportunities, maintain existing flow patterns, and provide storage of stormwater runoff on site. Stormwater BMPs must provide infiltration where feasible, but if infiltration is shown as not feasible for a site due to physical or contamination limitations, then another stormwater BMP may be used with preference for stormwater reuse. Water discharged to BMPs shall be pretreated to National Urban Runoff Program (NURP) standards. • National Pollution Discharge Elimination System (NPDES) Standards The MPCA is responsible for implementing NPDES standards. The NPDES requirements in the AUAR area will be from the NPDES Construction General Permit (effective August 1, 2023) and the NPDES Municipal Separate Storm Sewer System (MS4) Permit (effective November 16, 2020). The NPDES Construction General Permit requires that for sites replacing pervious surfaces with one acre or more of impervious surface, a water quality volume equivalent to 1 inch of runoff from the net increase of impervious surface should be treated. This can be met through wet sedimentation basins, infiltration/filtration, or regional ponding. There are three impaired waterbodies within the study area, and sites that are within one mile of impaired water bodies require additional BMPs. M:\027919-000\Admin\Docs\Stormwater\MEMO-021725-Stormwater AP.docx Page 77 of 240