Agenda Packets - 2021/07/06 - Laserfiche WebLink

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1.0 Executive Summary In an effort to ensure effective stormwater management and be in compliance with its Municipal Separate Storm Sewer System (MS4) permit, the City of Mounds View has begun an evaluation of its stormwater detention ponds. In 2011 the city selected Silver View Pond (see Figure 1) for evaluation to determine the amount of sediment that has accumulated since its construction, identify if it meets current treatment criteria. and determine if maintenance or upgrades are needed. The Silver View Pond assessment will also serve as a pilot assessment to help the city develop a process for per-forming a complete pond inventory and assessment for all of its stormwater ponds. This report surnntarizes Barr's findings and recommended actions for Silver View Pond. For the purposes of this analysis, only the stormwater detention and water duality treatment functions of Silver View Pond were considered. Other functions and values of the pond are not addressed in this document, but should be considered if the city snakes significant changes to the pond. Information about the original design and construction of Silver View Pond was obtained from tine City of Mounds View. This information was used to determine outlet elevations, the normal water level for the pond, and the originally excavated pond depth. The pond was also assessed to determine if it may have been built on or was a modification of a natural wetland. A survey of current conditions was conducted in 2011 on Silver View Pond to determine pond bathymetry, locate inlet and outlet structures, determine structure invert elevations and conditions, and estimate current accumulated sediment depths in the pond. Also, photos were taken of the inlet and outlet structures for the pond. 2011 survey data and historical data were combined with information about the immediate drainage area of the pond and land use for the pond drainage area to calculate the recommended design volume of the pond based on the Minnesota Pollution Control Agency (MPCA) Storrnwater Manual. The capability of the pond to remove total phosphorus and total suspended solids was also estimated. Incorporating extended detention by modifying the current pond outlet was also considered as a way to improve the water quality treatment efficiency of the basin since excavation may be very expensive or it may be difficult to obtain permits to work within the basin. The Silver View Pond assessment enables the City of Mounds View to understand the need for expansion, presence of wetlands, and overall project cost for upgrades to the pond. As part of the assessment, the need for and types of potential pond improvements were identified. The evaluation 1'! klrls'-3 NJN hA 2162 OF2 SONCT Vie" Pond Assessmem WorkrilcR HiJIPrt Solver Vieµ Pond Assessment-f final. d�+cx