08-04-25 - City Council Work Session Agenda

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• If present in or adjoining the AUAR area, the following types of water bodies must be given special analyses: o Lakes: Within the Twin Cities metro area, a nutrient budget analysis must be prepared for any "priority lake" identified by the Metropolitan Council. Outside of the metro area, lakes needing a nutrient budget analysis must be determined by consultation with the MPCA and DNR staffs. o Trout streams: If stormwater discharges will enter or affect a trout stream, an evaluation of the impacts on the chemical composition and temperature regime of the stream and the consequent impacts on the trout population (and other species of concern) must be included. Environmental Effects Stormwater runoff can cause a number of environmental problems. When untreated stormwater drains from man-made locations such as agricultural fields, impervious surfaces, and construction sites, it can carry sediments and/or chemical pollutants that harm aquatic ecosystems and wildlife. It is assumed that infiltration practices will not be allowed onsite due to the assumed presence of clay and organic soil and high ground water table. Prior to the creation of the extensive ditch system throughout the site, the area was a marsh. In the event infiltration requirements cannot be met on the site, alternate means of runoff abstraction and water quality treatment will need to be reviewed for the site to be in compliance with current watershed, state, and local stormwater management plans. The developments will need to follow the minimal impact design standard guidelines for alternative design as documented in the Minnesota Stormwater Manual for abstraction such as filtration, irrigation reuse, or other methods to meet the water quality and abstraction requirements. Existing Conditions In existing conditions, the study area is a mix of sod farm, low -density residential, and forested area. According to the City stormwater database, there are no stormwater management practices in place to treat stormwater runoff outside of the Century Farm Subdivisions in the southwest corner of the study area and a large stormwater quality basin constructed as part of the new roundabout at the intersection of Sunset Avenue and Main Street. The remainder of the study area has numerous ditches, county and privately owned, that were constructed in the mid- 1950s. The ditches have been realigned multiple times. Even with the existing ditch system, there is a significant portion of the site (-40-45% by area) that is covered in FEMA Zone A floodplain. Rice Creek Watershed District completed floodplain modeling and mapping in 2025 that shows similar, albeit less, floodplain areas within the study area. During Construction During construction, erosion and sediment control BMPs will be implemented to prevent impacts to aquatic ecosystems. The proposed alternatives include proposed impervious surfaces that vary depending on alternative and future design options. Additionally, the following design/construction standards are to be adhered to during construction: • Grading of the water quality basins shall be accomplished using low -impact, earthmoving equipment to prevent compaction of the underlying soils. • Water quality basin excavation shall be held 1 foot above the bottom of the excavation until the contributing drainage areas with exposed soils have been fully stabilized. Lino Lakes Main Street - AUAR 45 July 2025 Page 53 of 617