Development of a stormwater treatment train is an iterative process that balances site constraints, project goals, and available budget. The following steps lay out the process for establishing a stormwater treatment train. The results of one of the steps may cause designers to reconsider earlier decisions on sizing, siting, etc., as the project progresses.
Step 1 - Review project goals and site conditions
The site conditions, regulatory requirements, and project purpose will vary from site to site and from city to city. Information to assemble includes:
- Project goals – is the project intended to solve a drainage problem, meet regulatory requirements, or both? The answer to this question determines whether the goals are related to runoff volume or water quality. If the objectives are related to water quality, the pollutants of concern need to be identified.
- Regulatory requirements – are there any regulatory requirements that will influence the stormwater system?
- Site conditions: collect information on impervious surface, drainage area, runoff quality, soils, topography
Step 2 - Review pollutant removal processes and identify potential practices
The purpose of this step is to create a list of BMPs that work together to remove the pollutants of concern identified in Step 1.
- Select processes required to manage pollutants
- Identify combination(s) of BMPs that include the processes required to manage the identified pollutants
To make these determinations, use these tables, which provide information regarding processes and practices.
Step 3 - Determine site constraints that affect BMP placement and sizing
Site constraints will affect the sizing, location, and performance of the BMPs identified in Step 2. The purpose of this step is to narrow down the BMP options based on such site constraints as:
- Available space
- Access for maintenance
- Limitations on infiltration related to soil type, soil contamination, depth to groundwater, presence of structures, utility conflicts, and/or depth to bedrock
- Regulatory requirements that affect the BMP volume or footprint
- Compatibility with other site uses, including green space requirements, public spaces, structures, etc.
Step 4 - Select individual BMPs and evaluate range of performance
Review each BMP identified in Step 3 to confirm that each pollutant removal process identified in Step 2 is present in the combination of BMPs selected in Step 3. If not, then Step 3 should be reviewed and alternative BMPs proposed.
Step 5 - Size BMPs and assess performance
Size the BMP and use the MIDS calculator or other technique detailed in the Credits section of the MN Stormwater Manual to assess the performance. Review results against goals set in Step 1. If goals are not fully achieved, then resize the BMPs or return to Step 3 to select alternative BMPs.
Step 6 - Review construction and operation criteria
Designers should assess construction and operation considerations that need to be incorporated into the construction plans and/or the Operations and Maintenance Manual that are necessary to ensure the BMP operates as designed and is properly maintained.