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APPENDIX F City of Arden Hills WSB Project No. 3455-200 HYDRAULIC AND WATER QUALITY ANALYSES Regional Stormwater Treatment Locations There are thirteen proposed potential regional ponds in Arden Hills that were identified in a 1999 comprehensive drainage study by BRW Inc. (Dames and Moore Group Company). TCAAP property was not considered or modeled as part of this Plan. Two ponds within TCAAP, P-1 and P-13, will be completed as part of the reconstruction of TH 96, and will not be discussed in this Plan. The TCAAP Reuse Plan will include a preliminary layout of the stormwater management for the TCAAP property, meeting RCWD and other agencies requirements. The proposed regional ponds are mostly located in natural low lands or inlets to lakes. It should be noted that the City would need to further investigate the proposed regional pond locations with respect to jurisdictional wetlands and regulatory restrictions that may affect the construction of these facilities. Even though the BRW, Inc. study and this Plan evaluate the proposed construction of regional ponds, other stormwater treatment best management practices (such as infiltration BMP's) will be addressed in the feasibility study stage. The Minnesota Urban Small Sites BMP Manual (Metropolitan Council, 2001) outlines a three-step process to select a BMP or combination of BMP's for sites less than five acres. This process looks at stormwater treatment suitability, physical feasibility factors, and community and environmental factors. Summary Discharge Data HydroCAD® modeling was completed for the eleven proposed regional ponds. At this stage the ponds are only concepts, and therefore the modeling consisted of the drainage districts identified in the 1999 comprehensive drainage study by BRW, Inc. and the proposed concept pond. The concept pond was assumed to be rectangular in shape, with a ten-foot shelf below the normal water level, side slopes of 3:l everywhere else, and a depth of six feet. The 5, 10, and 100-year, 24-hour, storms were run, using antecedent moisture conditions II. The results of these models can be seen further in this Appendix. The 100-year design storm was used to calculate a peak height of the pond and to determine if any potential damage or flooding could occur at the neighboring structures. Only one pond as calculated from this modeling, P-12, has the potential for flooding the low point on North Hamline Avenue and will need more detailed analysis during the feasibility study/design stage to ensure no damage to the surrounding structures will occur. In addition to the HydroCAD modeling, stormwater quality and treatment modeling was undertaken using the P8 Urban Catchment model. Water Quality Analyses P-8 models were created for the proposed regional ponds. The ponds were designed to meet NURP (Nationwide Urban Runoff Program) standards, which are removal of 90% of total suspended solids (TSS) and 65% of total phosphorus (TP). As with the hydrologic modeling, no upstream drainage areas were used in the water quality modeling. The ponds were modeled using only the immediate drainage areas. Therefore, it is recommended to model the entire drainage system during either a feasibility study or final design to calculate the pollutant removal efficiencies of the entire system. The results from the P- 8 models can be found in this Appendix. Dr a f t 11 / 2 0 / 2 0 1 7