Agenda - Council - 10/27/2015 - Laserfiche WebLink

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3. Limiting discharge from the site for the 2 year, 10 year and 100 year storms to the existing rate for each storm. 4. Reducing the amount of Total Suspended Solids and Total Phosphorus in runoff leaving the site. These goals can be achieved through the following measures: 1. Construction of infiltration or water reuse practices on site such as infiltration trenches, rain gardens, tree trenches or water re -use practices. 2. Constructing detention facilities that retain the peak flow and discharge it at a slower rate. 3. Construction of wet ponds that provide adequate time for settling of the Total Suspended Solids and Total Phosphorus and prevent re -suspension with the next storm event. Observations/Alternatives: The City of Ramsey is bordered on the east by the Rum River and on the south by the Mississippi River. The City has many wetlands, lakes and streams within its borders. Managing the discharge of stormwater from developed sites is a critical component of preserving the water quality of the wetlands, lakes, streams and rivers in and adjacent to the City. The Surface Water Management Plan provides a framework for allowing development while maintaining surface water quality. The changes to the document include: • Updating City Code references to the current system • Updating the Stormwater management requirements for new construction • Infiltrate first 1" of runoff from new impervious surfaces • Provide rate control and water quality treatment for the 2, 10 and 100 year return events. • Provide reduction for Total Suspended Solids and Total Phosphorus concentrations in stormwater leaving the site. • Update the reference storms to use the Atlas 14 publication. The LRRWMO adopted use of the Atlas 14 and required the member cities to adopt this standard. • Remove references to wetland buffers for new construction. The City completed a Wetland Management Plan with the 2008 SWMP. The implementation of the Wetland Management Plan was postponed by City Council Action. • Update the Stormwater Models to include developments constructed after 2008 and use Atlas 14 for rainfall events. • Update the tables and figures to include the new model results. • The LRRWMO rules have specific provisions for protections of wetlands during construction. These requirements are preservation of vegetation within 16.5 feet of wetlands during construction and dedication of a drainage and utility easement encompassing this 16.5 buffer with the plat. This area may be sodded by the new homeowner. Implementing this change will require modifying our ordinances. Staff will be bringing this proposed ordinance revision to the Environmental Policy Board, Planning Commission and Council work session prior to introducing the ordinance at the Planning Commission. The tables and an overall map of the watersheds is attached for reference. The 10 year storm sewer capacity map and 100 year pond capacity map for the D43 watershed have also been attached to the case. The descriptions of the tables and maps is included in the plan. The adopted document will be available on the City website. Funding Source: Staff has performed the update to the plan as part of their normal duties. The Stormwater Utility Fund covers part of staff salaries. The plan lists Capital Improvement Projects that will need to be brought back individually for review and approval. Recommendation: Staff recommends approving the updated Surface Water Management Plan. Action: