Septic System Components: Drainfields – Part I


The Septic System Owners Manual / Septic System Components: Drainfields – Part I

  • Learn about the different types of drainfields.
  • Discover that the primary function of all drainfields is to return wastewater to the ground.
  • Learn that drainfields are designed to filter wastewater before it returns to the water table.
  • Learn that the most common cause of septic system failure is the drainfield becoming clogged and impermeable.
  • Discover that Aero-Stream can save a failed or failing drainfield by executing a controlled aerobic septic system conversion for under $1700!

Many people with septic system problems such as odor, slow draining sinks and tubs, gurgling pipes, backups and sewage water ponding in their yard mistakenly assume the cause of these issues is their septic tank.

This, however, is not true.

The most common cause of septic system failure is their septic system absorption component, more commonly known as a drainfield, becoming impermeable so that the wastewater can no longer be absorbed into the soil.

Drainfield Ponding1 - Septic System Components: Drainfields - Part I
Sewage collecting on ground above drainfield

Variations of Drainfields

There are many design variations of drainfields. A drainfield design depends upon many variables such as the size and topographical features of the lot, depth of the water table, soil conditions and types and other criteria. The size of the drainfield can vary infinitely, but most have minimum size requirements based on state and municipal codes.

The designs reviewed in this chapter are:

  • Gravity Drainfields
  • Pressure Distribution Drainfields
  • Cesspool (or Cesspit)
  • Drywell (or Seepage Pit)in Part II
  • Mound Systemsin Part II
  • Holding Tank in Part II
  • Aerobic Treatment Unit (ATU)in Part II


Gravity Drainfields:

As implied, gravity drainfields work by allowing the effluent to flow from the septic tank into a series of trenches by gravity. To allow this, the drainfield must be below the outlet level of the septic tank.

A conventional gravity system consists of a network of distribution components laid in gravel filled trenches. The trenches are dug in natural, undisturbed soil typically 3 feet above any natural occurring restrictive layer, such as a hardpan or the seasonal high water table.

in situ anaerobic typical - Septic System Components: Drainfields - Part I
Typical anaerobic gravity drainfield returning wastewater to the water table

The undisturbed soil filters out the remaining solids in the effluent which are then processed by anaerobic bacteria transported from the septic tank in the effluent.The anaerobic biochemical process cleans the effluent before it reaches the groundwater.

Maximum effectiveness of the final treatment occurs when the soil is dry and permeable. The size of the drainfield depends on the estimated daily wastewater flow (generally based on the number of occupants), soil type, and soil conditions.

Pressure Distribution Drainfields:

A pressure distribution drainfield is installed when the site conditions do not allow the drainfield to be installed at a lower elevation than the septic tank outlet, preventing the effluent to flow to the drainfield by gravity.Pressure distribution systems are similar in design to a gravity field and differ only by the use of a mechanical effluent pump to distribute the effluent from the pumping chamber or settling chamber to the drainfield.The pump is activated intermittently by use of a mechanical float device in the chamber where the pump is located.

Cesspool (or Cesspit):

A cesspool is a single chamber pit dug into the ground.

The soil walls are loosely lined with stone or brick to allow liquid effluent to seep out of the cesspool into the surrounding ground while holding the solids in the pit.

Cesspools used to be much more common and can still be found in some older homes. There are many problems associated with failing cesspools. As a cesspool fills with solids, the soil walls clog and become impermeable, preventing fluids to escape from the cesspool. This causes overflows until the cesspool is cleaned or a new cesspool is created.


All of these designs are subject to the same failure mode over time: they eventually become impermeable so that the sewage outflow from your septic tank cannot be absorbed into the ground.

Fortunately, you do not have to replace your drainfield to return your septic system to an operational condition. Aero-Stream® has developed a product and process that will fix and restore any type of failed drainfield. Learn more about our product and septic systems, in general, by navigating through our website, reading the Septic System Owners Manual, downloading the Septic System Report and calling us toll free.

cesspooll anerobic typical - Septic System Components: Drainfields - Part I
Typical anaerobic cesspool returning wastewater to the water table

The Septic System Owners Manual

Nobody plans for the expense of having septic tank problems. Whether your septic system is new or failing, this manual is a must read for any homeowner.Understand the causes and discover the solutions to your septic system and septic tank problems.