10/29/2003 Env Bd Packet - Laserfiche WebLink

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SRF Consulting Group, Inc. Storm Water Treatment BMP Utilization The proposed development project will exceed Rice Creek Watershed infiltration guidelines through the implementation of depressed storage areas, bioretention areas, and vegetated swale systems, see Drainage Area Figure (attached). Infiltration areas will reduce runoff discharge rates while also providing storm water treatment by infiltrating runoff through the soil. The bioretention areas in the proposed parking lots are designed to capture and infiltrate, at a minimum, the 0.34" rain event for the directly connected impervious areas. Storm water runoff is routed into the rain gardens through curb cuts in the parking areas. The slopes of the rain gardens are stabilized with erosion control mats to prevent soil erosion as the vegetation establishes. Larger storm events will be routed into the storm sewer system through overflow drop inlet structures located in each rain garden. The runoff from two north parking areas not connected to rain gardens is routed to the upper pond for treatment and rate control. The upper pond is designed to outlet either - 7. through a skimmer outlet structure during small storm events, or over a reinforced berm during larger events to a swale system that leads to the lower pond. The swale system will provide conveyance of water away from structures and parking areas to the lower pond during larger storm events. The lower pond is designed with enough active storage capacity to ensure controlled release through the designed outlet up through the 100 -year storm event. County Ditch 72 County Ditch 72, which comprises a drain tile line system, passes through the Eagle Brook development site Per the watershed district resolution, the system will be rerouted around the proposed development area and will continue to function as it does currently. The Rice Creek Watershed District has completed the necessary procedures (petition for abandonment and reestablishment, a public hearing and passage of a resolution) to allow the church to move the ditch to a new location. The church will continue to benefit from the ditch. The watershed district board of managers requested that the rerouted drain tile line remain as an underground system, which the church has incorporated into the construction plans (see submitted grading and utility plan sheets). Computations associated with the Stormwater Management Plan are attached to this permit application. Erosion Control Some potential for erosion during construction will exist as soils are disturbed by excavation. To minimize the potential, all exposed soils will be reseeded or sodded as soon as possible following construction. Best Management Practices (BMPs) for temporary and permanent erosion/sedimentation control are incorporated into construction plans in conformance with MPCA's requirements for the NPDES (National Pollutant Discharge Elimination System) Phase II permit for construction sites. BMPs H:\ Civil \047\4443\sent\BWBR \10 -17 -03 \City submittal narrative.doc