Septic Tank Styles & Systems

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Septic systems provide private sewage treatment for properties that are not connected to city sewer lines. Choosing the right septic tank style for you largely depends on the soil composition on your property. Gravity and pressurized systems typically require 2 to 3 vertical feet of native soil. The less soil available, the more complicated the septic system becomes.

Septic Tank Styles & Systems
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Understanding Septic Systems

Septic systems have three layers of materials: The sludge layer, the effluent and the scum layer. The sludge layer contains all of the solid waste that enters the septic tank and settles to the bottom. The effluent is the run-off water that sits above the sludge layer. The final layer is the scum layer, which floats on top of the effluent and contains lighter waste products.

Without removing the effluent in some way, septic tanks would fill up incredibly fast. Different septic tank styles have different ways of handling the effluent in order to safely and filter it out into the soil efficiently.

Gravity Septic Systems

A gravity system uses the force of gravity to move effluent from the first compartment to the second, then through an outlet pipe and to a distribution box. The distribution box ensures that the effluent passes through the drain field in an even manner. Long pipes with small holes distribute the effluent into the drain field, where microbes purify the water of any harmful bacteria before it settles into the surrounding soil and groundwater.

Pressurized Septic Systems

In a pressurized system, the effluent flows out of the second compartment and into another tank. A pump sitting at the bottom transfers the effluent from this tank to the distribution field. A pressurized septic system is preferable when the distribution field is located far away from the home. The pump does not run at all times – either a timer or an on-demand system can be used to ensure the pump remains efficient.

Mound System

A mound system is used in locations that lack the 2 to 3 vertical feet of soil required by conventional gravity and pressurized septic systems. Sand is built up into a mound to cover the drain pipes, which sit on top of the native soil instead of below. This tactic creates a suitable drain field for proper wastewater treatment.

Sand Filter System

In areas with less than 2 feet of native soil, a box with specially engineered sand creates an artificial drain field that cleans the effluent. Once the water is clean, it can then be pumped out – or flow via gravity – to the top of the native soil to filter into the groundwater.

ATU and Bio Filter

Manufactured systems, such as the Aerobic Treatment Unit (ATU) or the Bio Filter, use chemicals and special filters to clean the wastewater. These are typically used in locations with little to no suitable native soil to adequately clean the effluent naturally.


Cathy Habas enjoys distilling even the most complicated home improvement tasks into bite-sized pieces. She believes in empowering homeowners one article at a time.

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