Septic System Components: Drainfields – Part I

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

Introduction

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.

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 Systems – in 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.

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.

Conclusions

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.