Unless judged by the city to be exempt, the following performance criteria shall be addressed for storm water management at all sites equal to or greater than one acre:
(A) All site designs shall establish storm water management practices to control the peak flow rates of storm water discharge associated with specified design storms and reduce the generation of storm water. These practices should seek to utilize pervious areas for storm water treatment and to infiltrate storm water runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity.
(B) Annual groundwater recharge rates shall be maintained, by promoting infiltration through the use of structural and non-structural methods.
(C) Post construction Best Management Practices (BMPs) are installed after construction has been completed and the site has been stabilized. Installing certain BMPs, such as bioretention areas and sand filters, prior to stabilization can cause failure of the measure due to clogging from sediment. With a strict construction sequence, however, detention ponds and other BMPs can be installed initially during construction and used as permanent runoff control measures upon completion of construction activities. In those instances, the construction sequence must require that the pond is cleaned out with pertinent elevations and storage and treatment capacities reestablished as noted in the approved post construction runoff control plan.
(D) The city has adopted a policy that the control of storm water runoff quality will be based on the management of total suspended solids. For new development, BMPs shall be designed to remove 80% of the average annual post developmental total suspended solids (TSS). It is presumed that a BMP complies with this performance standard if it is:
(1) Sized to capture the prescribed water quality volume (WQv);
(2) Designed according to the specified performance criteria outlined in the city Storm Water Design and Construction Specifications Manual;
(3) Constructed properly; and,
(4) Maintained regularly.
(E) In addition to TSS removal, BMPs must also be designed to treat the water quality volume (WQv), or the first flush of runoff. All new development projects requiring post construction runoff control plans shall be required to treat the WQv. Redevelopment projects will be required to obtain storm water quality approval if the redevelopment activity disturbs more than one acre. Please refer to the city Storm Water Design and Construction Specifications Manual for further details regarding calculation of the WQv.
(F) The BMPs in Table 5.1 are acceptable for use in the city if designed, constructed, and maintained according to the criteria set forth in the city Storm Water Design and Construction Specifications Manual. It is presumed that these acceptable BMPs achieve a target TSS removal rate of 80% when correctly constructed and maintained.
(G) Should the developer/project site owner choose to implement a storm water control device, method, or system NOT listed as one of the acceptable BMPs for the city, the developer/project site owner must provide proof that the storm water control device, method, or system can achieve the target TSS removal rate of 80% when correctly constructed.
(Ord. 2004-13, passed 12-6-04; Am. Ord. 2007-5, passed 4-2-07)
Table 5.1—Acceptable BMPs for the City of Greensburg
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BMP Type | Description | Quantity Control | WQv and 80% TSS Removal | % TSS Removal Rate
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Table 5.1—Acceptable BMPs for the City of Greensburg
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BMP Type | Description | Quantity Control | WQv and 80% TSS Removal | % TSS Removal Rate
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Storm Water Ponds | Storm water retention ponds are constructed storm water retention basins with a permanent pool (or micropool) of water. Runoff from each rain event is captured and treated in the pool. | Yes | Yes | 85% |
Wet pond | ||||
Wet extended detention pond | ||||
Micropool extended detention pond | ||||
Multiple pond systems | ||||
Storm Water Wetlands | Storm water wetlands are constructed, artificial wetland systems used for storm water management. They consist of a combination of shallow marsh areas, open water, and semi-wet areas above the permanent pool | Yes | Yes | 95% |
Shallow wetland | ||||
Extended detention wetland | ||||
Pond/wetland systems | ||||
Pocket wetland | ||||
Bioretention Areas | Bioretention areas are shallow storm water basins or landscaped areas that utilize engineered soils and vegetation to capture and treat storm water runoff | No | Yes | 80% |
Sand Filters | Sand filters are multi-chamber structures designed to treat storm water runoff through filtration, using a sand bed as the primary filter media. | No | Yes | 85% |
Surface sand filter | ||||
Perimeter sand filter | ||||
Water Quality Swales | Water quality swales are vegetated open channels that are designed and constructed to capture and treat storm water runoff within dry cells. | No | Yes | 80% |
Dry swale | ||||
Biofilters | While biofilters provide some filtering of storm water runoff, by themselves they cannot meet the 80% TSS removal goal. These measures can only be used as pre-treatment measures or as part of a treatment train. | No | No | 60/30% |
Filter strip | ||||
Grass channel | ||||
Catch Basin Inserts | Catch basin inserts are small filtering devices installed in each catch basin to trap suspended solids and other pollutants. | No | Yes | 80% |
Various designs | ||||
(Ord. 2004-13, passed 12-6-04; Am. Ord. 2007-5, passed 4-2-07)