Requirements, recommendations and information for using underground infiltration BMPs in the MIDS calculator
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This page is in development and will contain guidance on using underground infiltration BMPs in the MIDS calculator
This page is in development and will contain guidance on using underground infiltration BMPs in the MIDS calculator
For an underground infiltration system, all stormwater captured in the underground pipe/storage device or in the underlying engineered media by the BMP is infiltrated into the underlying soil between rain events. All pollutants in the infiltrated water are credited as being reduced. Pollutants in the stormwater that bypasses the BMP are not reduced.
MIDS calculator user inputs for underground infiltration
For underground infiltration systems, the user must input the following parameters to calculate the volume and pollutant load reductions associated with the BMP.
- Watershed tab
- BMP Name: this cell is auto-filled but can be changed by the user.
- Routing/downstream BMP: if this BMP is part of a treatment train and water is being routed from this BMP to another BMP, the user selects the name of the BMP from the dropdown box to which water is being routed. All water must be routed to a single downstream BMP. The User must include the BMP receiving the routed water in the Schematic or the BMP will not appear in the dropdown box.
- BMP Watershed Area: BMP watershed areas are the areas draining directly to the BMP. Values can be added for four soil types (Hydrologic Soil Groups (HSG) A, B, C, D) and for three Land Cover types (Forest/Open Space, Managed Turf and impervious). The surface area of the BMP should be included as a managed turf land cover under the hydrologic soils group of the native soils located under the BMP. Units are in acres
- BMP Parameters tab
- Underground pipe/storage device storage volume below overflow (VP): The total storage volume in the pipe or storage device that is below the overflow. The storage device needs to be perforated to allow infiltration into the underlying soils. Methods for calculating the storage volume depend on the type of storage device used. Sample methods based on storage device can be found here. The user enters this value in cubic ft.
- Overflow depth between media and overflow (DO): The total depth between the outflow from the storage device to the underlying media. This value is used to calculate the drawdown time of the device to make sure it meets drawdown time requirements. The user enters this value in ft.
- Is engineered soil present below pipe/storage device?: The user enters ‘Yes’ if engineered soils designed to add storage capacity in increase infiltration are present below the storage device.
