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Sand Filter Septic System Design, Use, Maintenance, Repair InspectAPedia®  -

• Design & use of septic media filters using sand
• Septic filter capacity, maintenance, dosing control

This document discusses design and use of septic media filters using sand.

When using a septic media filter system, effluent treatment is by both actual filtration and ultimately by a biochemical process as the filter "matures" and includes its own biomass. This is particularly true of sand-bed filter septic systems which also often use a recirculating sand bed design to move septic effluent multiple passes through the sand filter system.

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Septic Media Filters Using Sand

Various texts cite the critical importance of selecting the proper sand for a septic media filter. New York's standard specifies a sand grain size of 0.25 to 1.0 mm; if nitrification is required (which may be specified by the local health department), the grain size is larger, 0.5mm to 1.0 mm., and all sand is passed through a 1/4" sieve and must be uniform to a coefficient of 4.0.

The effluent collector pipes below the sand bed discharge the treated effluent to an absorption system such as a drain field placed below the original ground level or possibly into a raised bed or mound system. The raised bed or mound receiving the treated effluent may itself be constructed of sand or other fill material with a percolation rate of not faster than 5 minutes per inch.

Typical sand filter construction (NY State Wastewater Standards) involves an excavated bed area which is filled in layers of material as follows (bottom up):

1. Collector pipe system set in gravel sized 3/4" to 1.5" aggregate.
2. 4" of aggregate above the collector pipes
3. 3" of crushed stone or clean gravel sized 1/8 to 1/4" atop the aggregate.
4. 24" of approved sand. Jantrania points out that a geotextile fabric should not be placed below the sand and atop the gravel. Though some installers think that's a great idea to keep the sand out of the gravel, he points out that the fabric is likely to clog and lead to early sand filter bed failure.
5. Distribution pipes placed in a layer of aggregate providing 4" or more across the whole surface of the sand filter and with aggregate of at least 2" underneath and above the distribution pipes.
6. A geotextile, 2" of hay or straw, or untreated building paper is placed atop the bed to keep soil fines out of the filter.
7. 6" to 12" of topsoil is placed atop the sand filter bed system, mounded to encourage surface water runoff to drain off of the system. The topsoil is seeded to grass.

Sand filter problems: keep deep rooting plants, surface runoff, and heavy traffic (that could compact the media) off of the system. Don't block air movement over the surface of the system with buildings or plantings.

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More Reading on Sand Filter Systems

Using a Sand Bed Effluent Disposal System as a Component of Alternative Septic Systems for Difficult Sites. This document includes the NYS Appendix 75-A section on sand filter beds (next citation) as well as sand filter bed design comments and advice from other experts

Sand Septic Filters - New York State Appendix 75-A Design Details for Intermittent Sand Bed Filter Septic Systems

References for this Septic Media Filters Discussion

My text draws heavily on Dr. Jantrania &Gross's work and on New York State Water Treatment Standards.

New York State Wastewater Treatment Standards - Individual Household Systems, Appendix 75-A (1990), Public Health Law 201(1)(1).

New York State Alternative Septic System Design Regulations, Wastewater Treatment Standards - Individual Household Systems, Appendix 75-A, of Public Health Law 201(1)(1) 1990.

Anish Jantrania, Ph.D., P.E., M.B.A., Consulting Engineer, Mechanicsville VA, 804-550-0389
NOTE: be sure to examine Dr. Jantrania's new (2006) book,
Advanced Onsite Wastewater Systems Technologies which can be
ordered from his publisher.

The Septic System Owners's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000. IS N 0-936070-20-X

Onsite wastewater treatment systems, Bennette D. Burks & Mary Margaret Minnis. Textbook and reference manual on all aspects of onsite treatment. This is one of the best books we've reviewed on the subject, with an excellent balance of clear simple explanation and solid engineering. Topics: Soil & Site Selection, Hydraulics, System Selection & Design, Wastewater Biology, History & Mythology of Onsite Wastewater Treatment. $49.95, Hogarth House, Ltd, 800-993-2665 x327 to order *800 -993-2665 x327 (Univ. Wisc. Bookstore)

Boxerwood Gardens is an arboretum and nature center in Lexington VA, and the generous contributor of the illustration of a gravel-bed natural septic media filter system discussed above.

More Information on Building Diagnostic Inspections and Repairs

• Septic Filters & Graywater Filters in-tank septic filters or graywater filters to keep solids out of the absorption system


• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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