Unless judged by the Board to be exempt or granted a waiver, the following performance criteria shall be addressed for stormwater management at the applicable sites.
(A) The post-development runoff discharge from the project site must not exceed the pre-development discharge, based on the two-year, ten-year, and one-hundred-year peak storm events.
(B) All site designs shall establish stormwater management practices to control the peak flow rates of stormwater discharge associated with specified design storms and reduce the generation of stormwater. These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate (when possible) stormwater runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical, to provide treatment for both water quality and quantity.
(C) Annual groundwater recharge rates shall be maintained by promoting infiltration using structural and nonstructural methods.
(D) BMPs must be capable of removing 80% of the TSS load from post-construction runoff. Constructed BMPs listed in Table 54.11 are approved to meet this requirement. For the purposes of this requirement, TSS is defined as particles smaller than 125 microns in diameter. Larger material is considered part of the total solids load of the stormwater runoff.
(E) BMPs shall incorporate floatables control to capture floating debris and remove it as part of the routine maintenance of the BMPs. Standalone BMPs must include floatables control. For BMP systems, or treatment trains, at least one of the components of the BMP system, located after the last inflow point to the system, must provide control of floatables.
(F) Measures shall, at a minimum:
(1) Utilize one or more post-construction measures working in tandem to treat stormwater runoff and to increase the overall efficiency of individual and specialized measures;
(2) In combination with proper post-construction measure selection, design and development strategies must be selected and incorporated into the plan to reduce the contribution of pollutants from the project area to the post-construction measures. These strategies include, but are not limited to:
(a) Low-impact development (LID) and green infrastructure;
(b) When selected, infiltration measures must take into consideration the pollutants associated with runoff and the potential to contaminate groundwater resources. Where there is a potential for contamination, implement measures that pre-treat runoff to eliminate or reduce the pollutants of concern. Infiltration practices will not be allowed in wellhead protection areas.
(G) In addition to TSS removal, BMPs must also be designed to treat the water quality volume (WQv) or water quality flow rate. All projects requiring post-construction SWPPPs shall be required to treat the WQv or flow rate, depending on the selected BMP. Redevelopment projects will be required to obtain stormwater approval if the redevelopment activity disturbs more than one acre. Refer to the Indiana Stormwater Quality Manual or another technical resource for further details regarding the calculation of the WQv or flow rate.
(H) The BMPs in Table 54.11 are acceptable for use in the county if they are designed, constructed, and maintained according to the criteria outlined in the Indiana Stormwater Quality Manual. It is presumed that these acceptable BMPs achieve a target TSS removal rate of 80% when correctly constructed and maintained.
(I) Should they choose to implement a stormwater control device, method, or system not listed as one of the acceptable BMPs for the county, the developer or project site owner must provide proof that the stormwater control device, method, or system can achieve the target TSS removal rate of 80% and include floatables control when correctly constructed.
BMP Type | Description | Quantity Control | Quality and 80% TSS Removal | Floatables Control |
BMP Type | Description | Quantity Control | Quality and 80% TSS Removal | Floatables Control |
Stormwater ponds: Wet pond, wet extended detention pond, micropool extended pond, multiple-pond systems | Stormwater detention/retention ponds are constructed stormwater basins with a permanent pool (or micropool) of water. | Yes | Yes | Yes, when floatables control is implemente d at inlets or outlets to the pond. |
Dry detention or infiltration pond (must have upstream pretreatment) | Stormwater detention or infiltration ponds designed to hold water and release it slowly or infiltrate into the ground. | Yes | Yes, with infiltration or pretreatment | Yes, with infiltration, pretreatment, or outlet control |
Stormwater wetlands: Shallow wetland, extended detention wetland, pond/wetland systems, pocket wetland | Stormwater wetlands are constructed, artificial wetland systems used for stormwater management. They use natural processes involving wetland vegetation, soils, and microbes to improve water quality. | Yes | Yes | Yes |
Bioretention areas: Rain gardens or landscape depressions | Bioretention areas are shallow stormwater basins or landscaped areas that utilize engineered soils and vegetation to capture and treat stormwater runoff. | Yes | Yes | Yes |
Sand filters: Surface sand filter, perimeter sand filter | Sand filters are multi-chamber structures designed to treat stormwater runoff through filtration, using a sand bed as the primary filter media. | No | Yes | Yes |
Water-quality swales: Dry swale | Water-quality swales are vegetated open channels that are designed and constructed to filter stormwater runoff with vegetation and gentle slopes. Can be used as part of a treatment train, but do not meet 80% TSS removal | No | No | No |
Biofilters: Filter strip, grass channel | While biofilters provide some filtering of stormwater runoff, by themselves they cannot meet the 80% TSS removal goal. These measures can only be used as pretreatment measures or as part of a treatment train. | No | No | No |
(BC Ord. 2024-09, passed 7-8-24)