Ordinance - #13-01 - 02/26/2013 - Laserfiche WebLink

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(a) All development disturbing one (1) acre or more must provide water quality treatment and runoff rate control for all stormwater. (1) Water Quality Treatment. a. Water quality treatment shall consist of a stormwater basin (dead storage) below the normal outlet greater than or equal to the runoff from a two and a half (2.5) inch storm over the entire contributing drainage area, assuming full development. 1. The stormwater basin shall have an annual removal efficiency of sixty percent (60 %) total phosphorous and ninety percent (90 %) total suspended solids. 2. The average depth of a stormwater basin shall be greater than three (3) feet. 3. Skimmers shall be incorporated in the design of the outlet. b. Peak flow control shall be provided for the 2, 10, and 100 year storm peak discharges and post development rates shall not exceed pre - development rates. c. Stormwater basins shall be designed using an SCS Type 2 100 -year return twenty -four (24) hour storm, 5.9 inch event. (2) Volume Control. a. A volume equal to one (1) inch of runoff from all impervious surfaces shall be infiltrated on site. Infiltration or evaporation from a stormwater basin may not be counted toward this requirement. 1. Infiltration basing construction must follow the MN Stormwater Manual Chapter 12 -INF, Vol. 2, or future updates. b. Alternatives will be considered where infiltration may not be achieved on site. c. The Lower Rum River _Watershed Management Organization (LRRWMO), of which the City is a member, has established a Stormwater Impact Fund for projects that cannot meet the volume reduction requirements. The LRRWMO has also established a Volume Bank of available runoff retention Volume Credits. A sequencing process is outlined in the LRRWMO Third Generation Plan for utilizing the Volume Bank or paying into the Stormwater Impact Fund. Sec. 117 -392 (a) is hereby amended to read as follows (additions indicated as underline, deletions indicated as strip): (a) The applicant shall install, construct, or pay the city fees for all stormwater management facilities necessary to manage increased runoff, so that the discharge rates from stormwater treatment basins for the predevelopment 2 10 and 100 -year peak storm discharge rates are not increased. These predevelopment rates shall be based on the last ten years of how that land was used. Accelerated channel erosion must not occur as a result of the proposed land disturbing or development activity. An applicant may also make an in -kind or a monetary contribution to the development and maintenance of community stormwater management facilities designed to serve multiple land disturbing and development activities undertaken by one or more persons, including the applicant. Sec. 117 -392 (d) (2) is hereby amended to read as follows (additions indicated as underline, deletions indicated as strike): (2) Flow attenuation of treated stormwater by use of open vegetated swales and natural depressions, infiltration of the first one (1) inch of runoff from all impervious surfaces must be provided. Sec. 117 -392 (e) is hereby added to read as follows (additions indicated as underline): (e) Permanent stormwater facilities shall be placed in drainage and utility easements. A stormwater facilities declaration and easement agreement shall be executed for all facilities that will be