10/24/2012 Env Bd Packet - Laserfiche WebLink

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The developer is proposing to place 1 to 2 feet of rock in the basins of these ponds. The rock basin bottom would create a difficult maintenance issue and could very well look unsightly in a number of years when possibly cattails, cottonwoods and Boxelders get rooted in this area. Sedimentation created by rogue plants would create cleanout issues in the future and look unsightly. Recommend not having rock bottoms; however, the developer must sign maintenance agreements with City and Watershed for these ponds, and cleanout would be at his expense. The plan and agreement must address the cleaning out of the forebay and pond areas, and state that the ponds will be cleaned out when they are determined to be 1/3 full. The developer shows pond areas being sodded on top. All sod areas must be irrigated, whether the sod is inside or outside the pond. An oil separator system has been designed into the normal pretreatment ponds. The design includes a clay liner. This design has not been reviewed by the Rice Creek Watershed Board Engineers. The clay liner would create a dead pool area. Since these proposed pools are 4 foot deep it is recommended that the ponds be separated from the general public access. This design for oil separation and stormwater pretreatment has never been incorporated into any city projects. A design such as the oil separator system across the street eliminates pooling on the site and this would be preferable. Recommend a dry forebay system and separate oil separator /grit chamber system. Rice Creek Watershed District also indicated that the chamber type of oil separator /grit chamber would be preferable to a clay lined pond. The developer is proposing a wet seed mix for the forebay areas. A wet seed mix is a term generally associated with native grass and forbes. Native grass and forbes that grow in a wet environment do not grow in an inundated water environment. Therefore the result of this would be cattails and other aggressive rogue plants that would volunteer on the site. The end result in my opinion would be an un -kept appearance. In the past, landscapes with unkept appearances in front of businesses were not desirable. Recommend a dry forebay system and separate chamber -type oil separator system. In addition, the permanent pool forebays could possibl-y be a hazard. If the ponds are to stay in a-perpetual state of pooling, than fencing around the ponds should be installed, or at a m- inimum a bench placed in the grade scheme. No soils should be imported or exported from the site without permission from the City. Any soils brought on to the site must be similar in nature to the surface water /infiltration characteristics of the existing soils or recalculation of runoff rates be resubmitted to the Rice Creek Watershed District for review. • Storm Water Pollution Prevention Plan The Submitted Stormwater Pollution Prevention Plan (SWPPP) is complete except for a couple of things. The SWPPP must identify the project manager responsible for implementing the SWPPP, phone numbers that the City can call for SWPPP action when it is needed, where the SWPPP will be located on site, and where the required inspection sheets will be located on the site. •