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• Lower~Rum River Watershed Management Organization Andover-Anoka-Coon Rapids-Ramsey 2015 First Avenue; Anoka, MN 55303 To: Lower Rum River Water Management Organization From: Barr Engineering Company Date: September 18, 2006 Re: Permit #2006-21: Green Valley Greenhouse: Ramsey We have received plans and a LRRWMO permit for the expansion of the Green Valley Greenhouse located at 6530 Green Valley Road in Ramsey. The site is 39 acres in surface area with 12 acres of building coverage and 9 acre of paved and gravel surfaces. The propped project increase the building coverage to 13 acres and the paved area to 11 acres. The plans show that storm water from the site is to be conveyed to a storm water management basin to be • constructed on the south side of the site. The basin has been designed to meet the LRRWMO storm water management requirements. The 100-year frequency flood elevation of the basin, as calculated by MFRA is 881 M.S.L. The lowest floor elevation of the existing on-site structure is above elevation 884 M.S.L. The outlet from the basin is to provide skimming of floatable materials. The outflow from this basin will ultimately reach Trout Brook. Because of the use of the property, the LRRWMO may wish to consider requiring a gate installed in the outlet structure that could be closed during the majority of the time which would result in this basin being a retention basin. Chemicals that could wash-off the site would be retained within the basin thereby minimizing potential downstream water quality impacts. After intense rainstorm, .the outlet could be opened allowing for a drawdown should it be necessary. Because of the sand soils conditions in the area, the majority of the runoff contained within the basin will likely infiltrate into the subsoil Erosion control is shown to be installed at the limits of construction. It is our recommendation that the LRRWMO approve of the permit for this project subject to the following conditions: 1. All erosion control measures. must ve installed at the initial stages of construction and be maintained until all areas altered have been restored. 2. Upon completion of construction and restoration of disturbed areas, the permit applicant is • responsible for the removal of all erosion control measures installed throughout the construction site. C:\Documents and Settings\sjankowski\DeskrtopU,RRWMO\2006Pem~it memos\Irr0621.doc -413-