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types of septic systems

Septic Designs Are Changing with the Times

Conventional: gravity feed with no pump.

On sites with downhill slope, the pull of gravity usually is all that’s needed to take effluent (filtered wastewater) from a septic tank to the drain field for dispersion without the help of a pump. Wastewater entering the tank pushes the effluent out through an array of perforated pipes that feed it into a drain field.

A standard conventional system should consist of a good quality tank, sized appropriately for the number of household drains it serves, and a drain field that’s also adequate for the property.

A good tank, properly installed, should filter about two-thirds of the contaminants from the wastewater, and an effluent filter removes large particles before the effluent flows out into the drain field.

Pump Delivery: through a distribution box for even distribution, ultimately through a gravity feed.

On sites where the drain field is uphill from the septic tank, gravity obviously won’t work. Instead, one or more pumps are installed to send the effluent out to another treatment unit and/or into the drain field. Some high-quality pumps operate with a control panel that evenly distributes effluent throughout the day.


Pressure Dosed: pumped uphill, then sent to a system of pipes for even distribution.

Among non-standard septic systems, the least expensive to install and operate is a low-pressure dosing system that pumps effluent into the drain field several times a day.

This system consists of a series of tanks, or a compartmented tank, in which wastewater settles out, connected to a pump tank where a pump sends the effluent in “doses” to a system of pipes with holes drilled into them, laid in narrow trenches. Wastewater seeps from the pipes into the trenches and percolates into the ground, returning to the water table.

“Dosing” occurs three or four times a day, which allows time for the percolation process, in which soil particles filter solids and organic matter from the wastewater. Microbes in the soil break down the solids and kill the bacteria and pathogens in the wastewater.

Advanced Wastewater Treatment Systems/Pressurized Infiltrator

In protected wetlands or other environmentally fragile areas, or on lots too small for conventional drain fields, an alternative to a traditional septic system is needed. The solution is an advanced treatment system with an Aerobic Treatment Unit (ATU).

Advanced treatment systems are more expensive to install than traditional septic systems, but they are also more energy-efficient and are designed to reduce accumulated solid waste more quickly.

Just as a conventional septic system uses natural processes to properly treat waste materials, an Advanced Treatment System pumps oxygen into the ATU tank to naturally treat the wastewater and solids. The added oxygen breaks down sewage material, reduces bacteria and transforms nutrients.

ATU systems are easy to maintain and are relatively affordable. Regulations are changing to allow these systems for land areas that do not qualify for traditional septic systems, and they are rapidly becoming a viable option in challenging situations.