Sand Filter

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Traditional BMP

Sand filters are multi-chamber structures designed to treat stormwater runoff through filtration, using a sediment forebay, a sand bed, and typically an underdrain system.
 

Types of Sand Filters

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Surface Sand Filters

Surface sand filters are ground-level open air structures made up of pretreatment sediment forebay and a filter bed chamber.

Perimeter Sand Filters

Perimeter sand filters are enclosed systems typically just below the ground in a vault along the edge of a watertight area such as a parking lot.

Underground Sand Filters

Underground sand filters are for areas with limited space and for high density areas. They should only be considered where local communities allow this practice. Because underground sand filters require additional planning, maintenance and incorporation with the stormwater management plan, coordinate with the local community for specific maintenance concerns.

Sand Filter Maintenance

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Routine maintenance should be performed on sand filters. Note that if the sand filter includes a grass cover or vegetation, maintenance may be required at a higher frequency during the first year the sand filter is built to ensure proper establishment of grass cover or vegetation in the practice. For more information on vegetation in a sand filter, see [insert Link to Appendix D: Planting and Soul Guidance]

After a rainstorm, keep drainage paths, both to and from the area, clean so that water can be properly filtered. If the sand filter is not draining properly, check for clogging in the inflow and outflow structures. It is likely that the upper layer of the filter (top 2-3 inches) is clogged and will need to be removed and replaced.

In case of snow, make sure that snow does not pile up in the sand filter. In addition, check to make sure that materials used to de-ice the surrounding areas stay out of the practice to avoid clogging and further pollution.

Fertilizers should not be used during or after the establishment of vegetated filter strips. Pesticides should be used sparingly and only if necessary.  

Common Issues During Maintenance of Sand Filters

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Here are some of the common problems to be aware of when maintaining a vegetated filter strip. They include, but are not limited to, the following:

  • Sediment build-up
  • Clogging in the inlet and outlet structure
  • Clogging in the underdrain
  • Mosquitoes breeding in the practice
  • Ant mounds

Should the sand filter become a breeding ground for mosquitoes, the problem is likely with the sand media or the overflow structure.

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Sand Filters

Routine Maintenance Schedule
Schedule
Activity
Monthly
  • Check to see that the filter bed is clean of sediment, and the sediment chamber is not more than 50% full or 6 inches, whichever is less, of sediment. Remove sediment as necessary.
  • Make sure that there is no evidence of deterioration, spalling or cracking of concrete.
  • Inspect grates (perimeter sand filter).
  • Inspect inlets, outlets and overflow spillway to ensure good condition and no evidence of erosion.
  • Repair or replace any damaged structural parts. 
  • Stabilize any eroded areas.
  • Ensure that flow is not bypassing the BMP.
  • Ensure that no noticeable odors are detected outside the practice.

As needed or 4 times during growing season
  • Ensure that contributing area, sand filter, inlets and outlets are clear of debris.
  • Prune and weed to maintain appearance (if applicable).
  • Ensure that the contributing area is stabilized and mowed, with clippings removed.
  • Ensure that activities in the drainage area minimize oil/grease and sediment entry to the system.
  • If permanent water level is present (perimeter sand filter), ensure that the chamber does not leak, and normal pool level is retained.
Annually
  • If filter bed is clogged or partially clogged, manual manipulation of the surface layer of sand may be required. Remove the top few inches of sand, roto-till or otherwise cultivate the surface, and replace media with sand meeting the design specifications.
  • Replace any filter fabric that has become clogged.

Every 3-5 years or as needed
  • Remove and replace the top 2-3 inches of sand in the filter