Sand Filter Basins and Ponds

Sand filter basins or ponds are a best management practice and storm water control measure employed to help remove pollutants from runoff before it enters surface or underground water conveyances.

The Texas Commission on Environmental Quality published “Complying with the Edwards Aquifer Rules: Technical Guidance on Best Management Practices” and in section 3.2.6 it states:

Sand filters consist of basins that capture stormwater runoff and then filter the runoff through a bed of sand in the floor of the facility. These BMPs can be configured as either a single basin or as separate sedimentation and filtration basins. These facilities should be installed at grade to facilitate drying out of the sand between storm events.

The objective of sand filters is to remove sediment and the pollutants from the first flush of pavement and impervious area runoff. The filtration of nutrients, organics, and coliform bacteria is enhanced by a mat of bacterial slime that develops during normal operations. One of the main advantages of sand filters is their adaptability; they can be used on areas with thin soils, high evaporation rates, low-soil infiltration rates, in limited- space areas, and where groundwater is to be protected (Young et al., 1996).

sand filter system - stormwater maintenance

A diagram of a sand filter system with separate sedimentation and filtration basins is presented above.

Since their original inception in Austin, Texas, thousands of intermittent sand filters have been implemented to treat stormwater runoff. There have been numerous alterations or variations in the original design as engineers in other jurisdictions have improved and adapted the technology to meet their specific requirements. Major types include the Austin Sand Filter, the District of Columbia Underground Sand Filter, the Alexandria Dry Vault Sand Filter, the Delaware Sand Filter, and peat-sand filters which are adapted to provide a sorption layer and vegetative cover to various sand filter designs (Young et al., 1996).

Selection Criteria:

  • Appropriate for space-limited areas
  • Applicable in arid climates where wet basins and constructed wetlands are not appropriate
  • High TSS removal efficiency

Limitations:

  • Require more maintenance than some other BMPs
  • Generally require more hydraulic head to operate properly (minimum 4 feet)
  • High solids loads will cause the filter to clog
  • Work best for relatively small, impervious watersheds
  • Filters in residential areas can present aesthetic and safety problems

Cost Considerations:

Filtration systems may require less land than some other BMPs, reducing the land acquisition cost; however, the structure itself is one of the more expensive BMPs. In addition, maintenance costs can be substantial.

sand filtration basin underdrains

Most sand filtration basins have underdrains which may need to be flushed or replaced over time.

 

First Year Inspections: After initial installation of sand filter BMPs, they should be inspected quarterly and after large rainfall events during the first year.
Heavy Siltation: The filtration system can be clogged to heavy sediment deposition. All areas on the site that flow into the sand filter basin need to be completely stabilized prior to runoff entering.
Level Infiltration Area: By constructing and maintaining the infiltration area completely level, runoff will not gain velocity and will equally spread out any pollutants carried by it.
Regular Inspections: Inspection frequency should be between 1 & 4 times per year in more arid climates and between 4 & 12 times in more temperate climates.
Sand Removal: Removal of the sand is needed if runoff takes more than 72 hours to infiltrate or the effluent water does not seem to be treated as well as previous inspections.
Perforated Infiltration Piping: Cleaning and jetting of the under sand piping every 2 years, or as needed to maintain runoff infiltration rates of 72 hours or less.
Mowing & Vegetation Maintenance: Vegetation in sand filtration basins must be mowed between 2 & 12 times per year to maintain a height between 4″ & 18″.

Call us today to discuss options for inspections, maintenance and replacement of sand material. 210-201-6401 in Central Texas or 832-510-720 in Southeast Texas or 214-997-3154 in North Texas