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Mr. Michael Grochala May 23, 2025 Page 2 • Protect life, public and private property, and the natural resources from damage resulting from runoff and the dangers associated with flooding. Existinq Conditions The study area currently consists primarily of agricultural, single/multifamily/rural residential, commercial, industrial, and park/open space areas. The impervious surface is primarily made up of residential/commercial roofs and the existing roadways. The major roads include 20th Avenue, 80th Street, County Road 14, and Interstates 35E and 35W. There are four major watersheds within the study area. The west and central portion of the study area is part of the Peltier subwatershed. The north part of the study area is within the Hardwood Creek subwatershed and Upper Rice Creek subwatershed, and the southeast part is within the Clearwater Creek subwatershed. All of these subwatersheds drain to Peltier Lake through tile drain or county ditch systems. Future development will need to address any requirements that are established due to current regulatory standards adopted by the RCWD, City of Lino Lakes, and Minnesota Pollution Control Agency (MPCA). The MPCA has listed three water resources within the study area as impaired: Peltier Lake, Hardwood Creek, and Clearwater Creek. Peltier Lake and Hardwood Creek have approved Total Maximum Daily Load (TMDL)that provides additional guidance and requirements for pollutant loads. Approximately 67% of the study area consists of Group D soils, and the remaining area consists of Group A, B, and C soils, plus open water surface. These soil ratings are based on hydrologic soil classifications, with A soils having high infiltration rates even when thoroughly wetted. The infiltration rates for A soils range from 0.8 to 1.63 inches per hour(Minnesota Stormwater Manual). These soils consist chiefly of deep, well drained to excessively drained sands and gravel. Group A soils have a high rate of water transmission, therefore resulting in a low runoff potential. Group B soils have moderate infiltration rates ranging from 0.3 to 0.45 inches per hour when thoroughly wetted. Group B soils consist of deep moderately well to well drained soils with moderately fine to moderately coarse textures. Group C soils have a low infiltration rate of 0.2 inches per hour when thoroughly wetted. Group C soils include a layer that impedes downward movement of water and soils with moderately fine to fine structure. Infiltration is very low in areas with Group D soils, and the design of infiltration basins is not recommended in areas with Group D soils (per the MPCA National Pollution Discharge Elimination System Construction General Permit). Proposed Conditions The two development scenarios were considered in this analysis for proposed conditions. Existing conditions and two proposed land use classifications were evaluated using curve numbers from the NRCS. Stormwater management for either proposed condition can be provided through a combination of wet detention ponds and infiltration and filtration features. Achieving volume reduction and pollutant reduction through the use of infiltration may be challenging for a majority of the study area due to a majority D soils with low infiltration rates and a high groundwater table. Stormwater management via green infrastructure such as stormwater reuse has been and will continue to be encouraged by the City of Lino Lakes and RCWD to achieve volume reduction and pollutant removal requirements. Reuse will be evaluated before implementation for safety and protection of human health. RCWD has supported stormwater reuse projects in the area with District funds in the past. M:\027919-000\Admin\Docs\Stormwater\MEMO-021725-Stormwater AP.docx Page 76 of 240