Storm water management assessment memorandum

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TECHNICAL MEMORANDUM HDR ENGINEERING, INC. Table 2—Action Items Action �tem �escriptian Recornmended Time ��rr�nt to Comp�ate ltem The side bank near the northeast corner of the pond As soon as possible. A has experienced erosion and requires immediate repair measures. The vegetative buffer strip should be reestablished in that part of the pond to prevent further deterioration of the side bank. The grates should be installed over the inlet culvert and As soon as possible B the outlet culvert (downstream end) of the Orono wet detention pond. The vegetation around the downstream end of the During normal, C outlet structure of the pond should be trimmed where it scheduled maintenance impedes access to the outlet structure requiring periodic and as needed. inspection. A periodic inspection of the pond should be scheduled As needed D to keep the pond in operating and optimum condition. Comment Item A The northeast periphery of the Orono pond has undergone erosion and some cracks were observed in the side bank during the inspection visit. It was also noticed that the northeast side bank consists of the low cohesive soil with lots of small pebbles and rocks which might be due to construction of the storage facility (constructed after the pond ) further north of the pond. The top soil of the northeast side bank should be immediately replaced with the fertile cohesive soil and a seed mix should be sprinkled to develop a vegetative buffer strip in this part of the pond. The vegetative buffer strip will not only provide slope stability to the side bank but also improve the water quality and pollutant removal efficiency of the pond. Comment Item B The grate over the inlet structure and outlet structure (d/s end) at the Orono wet detention pond was not seen during the inspection visit. The provided design plan sheets do not include/show a grate over the inlet structure and the downstream end of the outlet structure. It is recommended that the grates should be installed over the inlet and outlet structure to trap the trash and debris and improve the water quality of the Orono wet detention pond. Comment Item C The degree and density of the vegetation around and in the pond is appropriate at this time. If the vegetation at the location of the inlet and outlet structures becomes excessive and impedes access for visual inspections, it should be thinned as needed. The growth of large trees should only be allowed where they will not impede the performance of the inlet and outlet structures and will not compromise bank stability. 11/4/2005 HDR PRO,IECT#32560 6 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION