5.2. SR 08-08-2011 - Laserfiche WebLink

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surfaces. Stormwater management for any scenario can be provided through a combination of wet detention ponds and infiltration features. The soils within the study area will likely provide ideal conditions for achieving volume reduction and pollutant reduction through the use of infiltration. Local Stormwater Man~ement Requirements Stormwater management within the future development of the study area must be in conformance with local requirements. Some requirements are more stringent than others. However, the development in the study area will demonstrate that all local standards are being met under proposed Stormwater management techniques. The following is a summary of major Stormwater management requirements which will be addressed by future development of the study area: • City Stormwater Management Requirements and Design Standards The City's Stormwater Management Ordinance and current design standards require 60% removal of total phosphorus and total suspended solids from the post-construction developed condition. The City also encourages the use of infiltration and regional treatment where it is practical and feasible to do so. National Pollution Discharge Elimination System (NPDES) Standards The Mississippi River is listed as impaired and is located within one mile of the study area. As a result, the post-construction water quality standards of the NPDES permit will require future development to provide treatment for the water quality volume of 1-inch of runoff from the new impervious surfaces. Infiltration BMPs must allow this volume to be fully infiltrated within 48 hours. Wet Ponds must provide extended detention for this volume by providing permanent pool storage of 1,800 cubic feet per acre of drainage area and by restricting discharges. • Non-degradation and Restricted Discharge The State of Minnesota's current non-degradation rules prohibit new and expanded discharges to surface waters designated as Outstanding Resource Value Waters (ORVW's). Specifically, this means no increase in storm water runoff volume or pollutant loads from the 1988 baseline landuse condition. The stretches of the Mississippi River and the Rum River which the City of Elk River drains to are designated as ORVWs. As a result, for the purpose of this analysis, it is anticipated that future development of the study area must meet non-degradation standards. Water Quantity and Quali , Analysis A water quantity and quality analysis was completed for the existing and proposed conditions within the study area. This analysis uses the assumptions and methods described in the Non-degradation Review and Loading Assessment developed for the City of Elk River in 2007. This analysis also assumes that Stormwater runoff discharges offsite under the baseline condition. If it is determined that the study area is landlocked, future development maybe required to retain all runoff onsite to City of Elk River Draft Alternative Urban Areawide Review July 2011 Page 40 of 84