Amended Soils Performance Criteria
For both new and redevelopment sites, MSD will presume amended soil disconnection to meet the performance criteria for a standalone water quality BMP when the impervious area treated is designed to drain into the disconnection area and the design satisfies the parameters listed in Table 1.
Table 1. Amended Soils Disconnection Design Criteria
| Design Factor | Disconnection Criteria |
|---|---|
| Maximum impervious area treated | 1,000 square feet |
| Minimum area of amended soils | Equal to area of impervious disconnect |
| Minimum width of amended soils | 10 feet |
| Longest flow path of impervious area | 50 feet |
| Disconnection length | Equal to the longest flow path of impervious area. No less than 20 feet for downspout disconnections. |
| Disconnection slope | 5% maximum |
Rooftop disconnection downspout discharge points should be located to drain away from the structure and to avoid potential erosion problems. Proposed uses and designs should also comply with current MSD Rules, Regulations, and Design Requirements.
Refer to Specifications for compost soil amendment description, procedures and material requirements.
Examples of a rooftop disconnection Example: Rooftop Amended Soils Disconnection and a trail disconnection Example: Linear Pavement Amended Soils Disconnection are provided to illustrate the BMP application and design criteria.