Today’s Septic Systems

gravity septic system The Gravity System, the Most Basic

The most basic type of septic system permitted today for long-term use is the conventional gravity system. It is comprised of the septic tank, the drain field, and the soil beneath the drain field. Wastewater flows from the house into the septic tank through the inlet baffle.

Heavy solids settle to the sludge layer on the bottom of the tan, while lighter materials float to the top forming the scum layer. The clear liquid in the middle is known as effluent. The effluent flows through the outlet baffle into the next component of the system. Filters designed to fit into the outlet baffle of your septic tank add an extra barrier to help prevent solids from moving into the drain field or other components.

Important Parts of the System 

If your system does not have a baffle filter, consider having one installed. And if you have a concrete baffle, you may want to have a retrofitted plastic baffle installed in its place. Baffles tend to degrade in septic tanks due to corrosive gases, so it’s important to clean your filter every 6 to 12 months.

Gravity systems typically utilize a distribution box (D box) to direct an equal amount of effluent into each lateral pipe in the drain field. Once the effluent reaches the laterals, it flows out of small holes and into the surrounding soil. As it percolates through the soil, aerobic or oxygen-loving bacteria and other microbes remove pathogens. This treatment is critical in protecting groundwater and surface water resources.

The perforated drain pipe sits on a level grade with a gravel layer, which provides a space for the effluent to move. A fabric layer is generally installed above the gravel to prevent the upper level of fine soil from moving down into the gravel.

Pressurized Systems Used to Move Wastewater On the Property

Sometimes, the wastewater needs to be moved to a specific part of the property. In that case, pressurized systems may be used to pump the wastewater to the proper location. They are also used when the soil type requires a specific dosing, or when vertical separation is not deep enough.

The pressurized system starts with the septic tank , but after the septic tank the wastewater flows into a pump tank. From there it's pumped to the drain field where it is spread equally throughout the drain field lines. A pump tank requires a certain water level ensure the pump is covered; if the water level drops below the pump, the pump could overheat and become damaged. There are, however, elements built into the pump tank to help minimize that eventuality.

Alternative Systems

mound septic system
The Mound System

Mounds are used when there are only one or two feet of suitable native soil. Building a mound provides additional vertical separation, and the mound is created from specially engineered sand. Wastewater enters at the top of the mound, then percolates down through the sand to the native soil below.

sand filter septic system

The Sand Filter System

A sand filter is basically a box of engineered sand and gravel which treats the wastewater. This system requires only 1 ½  to 2 ½ feet of suitable native soil. Wastewater enters at the top of the sand filter and is treated as it flows down through the sand and gravel. The pre-treated wastewater then flows either by pressure or gravity to a drain field. There it receives final treatment and is dispersed.

Proprietary Systems

There are several proprietary systems for properties lacking sufficient native soil depth.

An anaerobic treatment unit needs only a minimum of 12 to 18 inches of soil. In this system, a blower aerator injects air into a tank, which enhances the aerobic microbial action. Often, this type of system requires some form of disinfection (like chlorine or UV treatment) before the wastewater enters the drain field. The manufacturers of this type of proprietary device generally require inspection by their certified representative once, and sometimes twice, annually.

Another type of proprietary system is the bio filter. Bio filters are designed and installed where there is as little as one foot of suitable soil available. Bio filter-approved professionals are needed to design, install and perform maintenance on these systems. Your local health department can provide more details.


Less Vertical Separation Means Simpler Systems, Higher Costs

In general, as the vertical separation decreases, the complexity of the system increases. Unfortunately, so does the cost, with alternative systems running thousands of dollars more than your basic system. Maintenance requirements are greater, too.

Give us a call today, and we will be glad to help you determine what sort of system your property requires.

All images courtesy of the US EPA