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Fact Sheet: Septic Systems – Subsurface Sandfilters

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Septic Systems – Subsurface Sandfilters

Distribution Box: This box, located at the inlet to the sandfilter, divides the effluent flow from the septic tank and spreads it over the surface of the filter. Effluent from the septic tank either flows by gravity or is pumped into this box.

Perforated Leaching Pipes: These pipes distribute effluent over the sandfilter bed.

Subsurface Sandfilter: The sandfilter is constructed from two layers of gravel and one layer of filter sand. Effluent passes through perforated pipes and trickles through the upper gravel layer.

This process slows and aerates the water. As the water passes through the sand and bottom gravel layer, naturally occurring bacteria remove toxins, bacteria, viruses and other pollutants.

Chlorinator: As filtered effluent passes through the chlorinator it is further treated with chlorine tablets. The disinfected effluent is then discharged to a stream or other drainage course.



Check your chlorinator regularly. Keep a small number (5-10) of chlorine tablets in each supply tube. Do not fill to capacity. If moisture causes tablets to swell, clogging the supple tube, the clog must be removed for proper chlorination to occur.

Caution: Tablet chlorine is a strong irritant. Protective gloves and eyewear should be used when handling tablets. When purchasing tablets, ask your supplier for a safety data sheet and always follow the instructions.

Warning: Chlorine used for swimming pool disinfection is not formulated for use in sewage system chlorinators. Using pool chlorine tablets in a sewage system chlorinator is a Federal offense.


Risers and Lids

To prevent entrance of surface water, access ports used for inspection and maintenance should be extended 4-6 inches above the surrounding ground surface. If access lids are at the surface or buried, use concrete or plastic riser sections to bring the lids above the grade. Lids that cannot be moved without cracking or falling apart must be replaced.


Discharge Point

Periodically check the location where your system discharges. If discharged effluent is not clear, black/grey in color or smells like sewage, call a service contractor. The end of the discharge line must be uncovered, free of debris and free-flowing. Discharge points are not appropriate play areas for children even when systems are operating properly.


Why Maintain your System?

There are three main reasons why septic system maintenance is so important:

  • Money – Poor maintenance is a common cause of early system failure. The minimal amount of preventive maintenance a septic system requires costs very little compared to the cost of repair and replacement.
  • Health – When a septic system fails, inadequately treated household wastewater is released into the environment. Direct contact with poorly treated human waste can pose significant health risks. Untreated wastewater can also contaminate nearby ground and surface water.
  • Economic Health of Community – Failed septic systems lower property values and contribute to the pollution of local rivers, lakes, and ponds used for commercial or recreational activities.


Managing your System

Protect your septic system from potential damage. Only plant grass near your septic system – roots from shrubs and trees can cause damage. Don’t allow heavy machinery over any part of the system. Never build anything over the drainfield.



All contracted repairs must be performed by registered professionals. A list of registered pumpers and contractors is available on the Health District’s Web site,, or by calling 513/946-7862.

Permission granted by The National Small Flows Clearinghouse, Pipeline Newsletter.



For more information, contact the Water Quality Division at 513.946.7862 or visit


Download a printable version of this fact sheet here.


250 William Howard Taft Road
2nd Floor, Cincinnati, OH 45219
Phone 513.946.7800 Fax 513.946.7890