SAND FILTER FOR TREATING STORM WATER RUNOFF
Revision Date: 01/04
Process Code: Navy/Marines: SER-016-99; Air Force: FA08; Army: N/A
Usage List: Navy: Low; Marines: Low; Army: Low; Air Force: Low
Alternative For: Wet ponds, infiltration basins, infiltration trenches, extended detention dry ponds, vegetated filter strips, and grass swales
Compliance Impact: Low
Applicable EPCRA Targeted Constituents and CAS Numbers: Lead (CAS: 7439-92-1) and Phosphorous (Yellow Or White) (CAS: 7723-14-0)
Overview: Sand filters can be used for storm water quality control and managing storm water runoff volumes. Sand filters are composed of at least two components: a sedimentation chamber and a filtration chamber. The sedimentation chamber removes floatables and heavy sediments, while the filtration chamber removes additional pollutants by filtering flow through a sand bed. Treated filtrate is normally diverted back to the storm drainage system via an underdrain system or pipe network. Pollutants such as suspended solids, biochemical oxygen demand (BOD), total phosphorus, and fecal coliform bacteria are effectively removed from storm water flows when treated by a sand filter system. Other pollutants removed include phosphorus and metals. Sand filter designs include the surface sand filter basin (AKA Austin sand filter), the underground vault sand filter (Washington, DC sand filter), the double trench sand filter (Delaware sand filter), the stone reservoir trench sand filter, and the peat sand filter system. Modifications are often made to these designs based on site-specific conditions.

Sand filters provide a highly effective means of removing pollutants from storm water while remaining flexible in application to allow for modifications in basic design structure to accommodate site-specific criteria. Modifications to the basic structure arise due to site differences, including drainage area served, filter surface areas, land requirements, and quantity of runoff treated. Sand filters are currently popular best management practices (BMPs) used in Delaware; Florida; Austin, Texas; Alexandria, Virginia; and Washington, DC.

The Austin sand filter was designed to detain runoff in a sedimentation chamber where heavy sediments and floatables are removed. Estimates of pollutant removal efficiencies for various Austin sand filters, based on the preliminary findings of the city’s storm water monitoring program, are as follows. In addition, data from an intermittent sand filter (Delaware sand filter), constructed to treat runoff from a commercial parking lot near Ronald Reagan National Airport in Alexandria, Virginia, are provided below.

Table 1. Sand Filter Data

Pollutant

Austin sand filter

Delaware sand filter

Fecal Coliform

76 %

not measured

Total Suspended Solids (TSS)

70 %

80-83%

Biochemical Oxygen Demand (BOD)

70 %

77.5%

Total Organic Carbon (TOC)

48 %

65.9%

Total Kjeldahl Nitrogen (TKN)

46 %

70.6%

Iron (Fe)

45%

not measured

Lead (Pb)

45 %

not measured

Zinc (Zn)

45 %

81.6%

Total Phosphorous (TP)

33 %

72.3%

Total Nitrogen

21 %

47.2%

Nitrate as Nitrogen (NO3--N)

0 %

62.7%

The percentages listed for the Austin sand filter include partial and full sedimentation systems with different drainage areas. Current monitoring data from the Austin sand filters indicates phosphorous removal efficiencies of up to 60 percent. The Austin sand filter also has been used in Alexandria, Virginia; monitoring of these units indicated a phosphorus removal of up to 40 percent. Nitrate was not removed nor is it known what the removal efficiencies are for other dissolved pollutants.

Performance of sand filters may be sustained through frequent inspections and replacement of the filter fabric and the top of the media every three to five years, depending on the pollutant load being treated. One system has been reported to need filter changes two times per year due to heavy pollutant loads. Accumulated trash and debris should be removed from the sand filters every six months or as necessary. Performance also can be increased by stabilizing the drainage area to minimize sediment loading, ensuring that the sedimentation chamber adequately removes suspended solids and sediments prior to the filtration chamber and allowing for adequate detention times for both sedimentation and filtration.

The design of sand filters with impermeable chambers that prevent groundwater infiltration are preferred in situations where groundwater contamination is a concern. The Austin, Delaware, and Washington, DC, sand filters may substitute for water quality inlets when hydrocarbons are of concern. Due to the size of the Austin sand filter, it also can be used instead of wet ponds for treatment of contaminated run-off in areas where evaporation exceeds rainfall.

 

Compliance Benefit: The use of a sand filter for treating stormwater runoff may help facilities meet the conditions and requirements contained in stormwater permits and stormwater pollution prevention plans as well as 40 CFR 122.26.

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.
Materials Compatibility: No materials compatibility issues were identified.


Safety and Health: Safety and health concerns depend on the types of contaminants in the stormwater. Metals and phosphorus, for instance, require caution in handling. They are skin irritants. Protective gear should be worn when handling contaminants such as fecal coliform. Proper personal protection equipment is, therefore, recommended. In addition, care should be taken when working with sealed systems, as gas may accumulate.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any of these technologies.

 
Benefits:
  • Sand filters, in particular those mentioned previously, achieve high removal efficiencies for suspended solids, BOD, and fecal coliform bacteria, and total phosphorous.
  • Hydrocarbons and nutrients also are removed by sand filters.
  • Sand filters designed with impermeable basins limit the potential for groundwater contamination while treating storm water.
  • Sand filters can be used in small sites (e.g., gas stations or other urban settings) where a wet pond is not possible due to spacial constraints.

 

Disadvantages:
  • Nitrates are not removed.
  • Sand filters are ineffective in removing dissolved pollutants except by adsorption.

Economic Analysis: Construction costs vary depending on the sand filter system being designed. The Austin sand filtration system costs approximately $18,500 for treatment of a 1-acre drainage area. In this instance, the cost decreases with increasing drainage area. Cost per acre decreases as the number of acres served increases. For example, the cost for a sand filter decreases to approximately $2,360/acre when treating 30 acres. The precast cost for one impervious acre for a Washington, DC, sand filter is approximately $25,000 to $30,000. Costs for the Delaware sand filter are $20,000 per impervious acre treated.

Assumptions:

  • The following comparison uses an average cost of sand filters.
  • Maintenance costs for a sand filter average 5 percent of the construction cost.
  • Labor costs for operating a wet pond include mowing and debris removal.
  • Labor costs for operating a sand filter include filter changing, gravel and sand replacement, and debris removal, estimated at approximately 3 hours/year.
  • Material costs for the gravel layer, filter fabric, and top portion of sand based on the experience of the Washington, D.C., sand filter are approximately $1,700 annually.
  • The figures in the table are based on one impervious acre treated.
  • The cost per pound of pollutant removed equals $8.30 based on the experience for the Washington, D.C. sand filter.
  • Labor costs are $45/hour.
  • Materials disposed are not hazardous. Solid waste disposal costs are $40/ton or $0.02/lb.
  • Annual disposal of sediments is 350 lbs.

Table 2. Annual Operating Cost Comparison for Wet Ponds and Sand Filter

 

Wet Pond

Sand Filter

Operational Costs:

    

Labor:

$1,620

$135

Materials:

$0

$1,700

Waste Disposal:

$7

$7

Total Costs:

$1,627

$1,842

Total Income:

    

Annual Benefit:

-$1,627

-$1,842

Economic Analysis Summary:

  • Annual Savings: -$215
  • Capital Cost for Equipment/Process: $20,000
  • Payback Period for Investment in Equipment/Process: N/A

Overall costs for installing and operating a sand filter system appear to be higher than that of using a wet pond system. However, in many urban situations, it is not feasible to install a wet pond. A sand filter is an effective alternative for treating stormwater runoff.

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NSN/MSDS: None identified.
Approving Authority: Appropriate authority for making process changes should always be sought prior to procuring or implementing any of the technologies identified herein.

 
Points of Contact: For more information

Vendors: This is not meant to be a complete list, as there may be other manufacturers of this type of equipment.

Pipe & Precast Construction Products, Inc.
Old Phoenixville Pike
P.O. Box 425
Devault, PA  19432
Phone: (610) 644-7338
FAX: (610) 644-8682
Contact: Mr. Bruce Smith

Gillespie & Son, Inc.
P.O. Box 450
Chestertown, MD  21620
Phone (800) 638-6884 or (410) 778-0900
FAX: (410) 758-0361
Contact: Mr. James Talbott

National Concrete Products
P.O. Box 2001
Greenwood, DE  19950
Phone: (302) 349-5528
FAX:  (302) 349-9435
Contact: Mr. Matthew McCombs

 

Related Links: Do You Discharge Non-Point Source Pollution To Water Supplies? -- Navy Environmental Quality Initiative (EQI)
Do You Maintain A Storm Water Pollution Prevention Plan? -- Navy Environmental Quality Initiative (EQI)
Storm Water Phase II Final Rule Fact Sheet Series, EPA


Sources:

Mr. Randy Greer, Department of Natural Resources and Environmental Control, November 1999.
Mr. Peter B. Drottar, Bolling Air Force Base, January 1999.
Bell, W. M. and T. N. Nguyen, 1993. Structural Best Management Practices for Stormwater Quality in the Ultra-Urban Environment. Water Environment Federation 66th Annual Conference & Exposition. AC93-032-007.
Bell, W.M. and T.N. Nguyen, 1996. BMP Technologies for Ultra-Urban Settings. Effective Land Management for Reduced Environmental Impact. Tidewater’s Land Management Conference on Water Quality.
Bell, W.M. and T.N. Nguyen, 1995. Intermittent Sand Filter BMPs for Stormwater Quality. Watershed Protection Through Stormwater Management Regulation and Design for New Developments, Montgomery County, Maryland.
Bell W.M. et al., Assessment of the Pollutant Removal Efficiencies of Delaware Sand Filter BMPs, City of Alexandria, Virginia, Department of Transportation and Environmental Services.
Shaver, Earl, 1991. Sand Filter Design for Water Quality Treatment. Delaware Department of Natural Resources and Environmental Control.
Troung, H. 1989. The Sand Filter Water Quality Structure. District of Columbia.
City of Austin, Texas, 1988. Design Guidelines for Water Quality Control Basins. Environmental Criteria Manual.
Galli, John, 1990. Peat-sand Filters: A Proposed Storm Water Management Practice for Urbanized Areas. Metropolitan Washington Council of Governments, Washington, DC.