Filtration

Information: The original Manual combined several filtration practices, including sand filters and swales, into a single chapter. We eventually will break some of these practices out into separate chapters. For now, they continue to be combined into single pages shown below. NOTE that we have included links to images for sand filters and swales in the outline below.

Filtering practices include media filters (surface, underground, perimeter), vegetative filters (filter strips, grass channels), and combination media/vegetative filters (dry swales). Media and media/vegetative filters operate similarly and provide comparable water quality capabilities as bioretention. Vegetative filters are generally more suitable as pretreatment practices, but in some situations can be used on a stand alone basis.

Filtering practices have widespread applicability and are suitable for all land uses, as long as the contributing drainage areas are limited (e.g., typically less than 5 acres). Media filters are not as aesthetically appealing as bioretention, which makes them more appropriate for commercial or light industrial land uses or in locations that will not receive significant public exposure. Media filters are particularly well suited for sites with high percentages of impervious cover (e.g., greater than 50%). Media filters can be designed with an underdrain, which makes them a good option for treating potential stormwater hotspots (PSHs). They can also be installed underground to prevent the consumption of valuable land space (often an important retrofit or redevelopment consideration). Vegetative filters can be incorporated into landscaped areas, providing dual functionality.

The individual articles comprising this section on filtration may be viewed as a single article. Note: Due to an unresolved bug, when viewing a formula in a combined article, the math markup (used for equations) is displayed. Please ignore the markup. Thanks.

• Overview for filtration
• Types of filtration
• Design criteria for filtration
• Construction specifications for filtration
• Assessing the performance of sand filters
• Assessing the performance of swales
• Operation and maintenance of filtration
• Calculating credits for sand filter
• Calculating credits for dry swale (grass swale)
• Cost-benefit considerations for filtration

References for filtration

Minimal Impact Design Standards pages

Warning: If you are using a swale for stormwater infiltration in the MIDS calculator, and the project requires a construction stormwater general permit, you must comply with all construction related requirements found in the permit.

• Swale Main Channel: Requirements, recommendations and information for using swale without an underdrain as a BMP in the MIDS calculator
• Requirements, recommendations and information for using swale with an underdrain as a BMP in the MIDS calculator
• Requirements, recommendations and information for using swale side slope as a BMP in the MIDS calculator
• Requirements, recommendations and information for using wet swale as a BMP in the MIDS calculator
• Requirements, recommendations and information for using sand filter as a BMP in the MIDS calculator

Links to CADD files

Links to detail images

• Sand filters
  • Perimiter sand filter details: File:Perimeter Sand Filter PERIMETER SAND FILTER DETAILS (1).pdf
  • Surface sand filter: File:SURFACE Sand Filter3 Surface sand filter (1).pdf
  • Underground sand filter: File:UNDERGROUND SAND FILTER Layout2 (1).pdf

• Swales
  • Swale layout: File:Swale Layout2 (1).pdf
  • Typical grass channel sections and design matrix (with and without soil amendment): File:MIDS Dry Swale Sections-SHEET 1.pdf. Contains the following cross-sections.
    • Typical grass channel without soil amendment
    • Typical grass channel with soil amendment
  • Typical dry swale with check dam and draintile: File:MIDS Dry Swale Sections-SHEET 2.pdf. Contains the following cross-sections and profiles:
    • Typical dry swale check dam
    • Typical dry swale check dam with draintile
    • typical dry swale with draintile
    • typical dry swale profile section with check dams
    • typical dry swale profile section with check dams and draintile

Fact sheet for filtration