Types of  Septic Systems

All septic systems have a septic tank.  The type of septic system is defined by the type of absorption field used to treat and dispose of the wastewater.  There are basically four types of septic systems allowed in Utah:

• Conventional  Septic Systems

and the following  Alternative Onsite Sewer Systems:

• At-Grade Systems*

• Earth Fill Systems*

• Mound Systems*

* There are three types of "Alternative Systems" allowed in Utah.  These systems may or may not be allowed by your local Health Department.

Conventional Septic Systems

Conventional Septic Systems are defined in "What is a Septic System."  These systems can be subcategorized by the type of absorption system used. 

Standard Absorption Trench.  Standard trenches are narrow, 1 to 3 feet wide, and have one distribution pipe per trench.  Trenches are generally more desirable than absorption beds because trenches can provide five times more absorption area than beds and can be used to follow contours on sloping sites.

Absorption Bed.  Absorption beds consist of a wide trench with more than one distribution pipe.  Absorption beds may be preferred when the potential site is level and soils consist of sands and loamy sands (perc rate between 1 and 30 min/in).

Deep Wall Trench.  A deep wall trench is similar to the standard trench except the  depth of the trench below the distribution pipe is 2 or more feet.  A deep wall trench may be used to reach more permeable soils at depth if groundwater is not a problem.

Chambered Trench Systems. 

Chambered systems, typically made of plastic, with a large internal void space, are placed end to end in the bottom of a trench and backfilled with natural soil.  Chambered systems are used in a trench instead of gravel fill.  You can find out more about chambered trench systems at www.infiltratorsystems.com.

Alternative Onsite Sewer Systems

There are three types of "Alternative Systems" allowed in Utah.  These systems may or may not be allowed by your local Health Department.  At the time this was written, there were only a few Health Departments in Utah that allowed Alternative Onsite Sewer Systems.   Since other Health Departments are in the progress of getting approval to allow these Alternative Systems in their districts, it is recommended that you check with your local health department.  For those who live up in the mountains, keep in mind, you can build a conventional septic system on an existing site slope of 25% or less.  Alternative Onsite Sewer Systems in Utah may only be built on an existing site slope of 4% or less.

At-Grade Systems

At grade systems are similar to a conventional system except that they are installed at the soil surface.  They are generally used in areas where a shallow groundwater table or shallow bedrock prohibits the use of a conventional system.  In Utah, the bottom of the absorption field must be 24" from groundwater and 48" from bedrock.  An advantage of the At-Grade System is that effluent enters natural soils that usually have the highest permeability and provide the best treatment. 

Earth Fill Systems

An Earth Fill System is a system where suitable soil (earth fill) is brought in between the bottom of the absorption system and the natural soil surface.  These systems are used where a high groundwater table or inadequate depth to an impervious layer are encountered.  These systems can be costly because they must be sized for a minimum of 3 bedrooms, perc rate of 60 min/in, and the area of fill must include a 100% replacement area.  The earth fill must sit for a minimum of a one year for stabilization and must have a perc rate of 15 to 45 min/in after that time.

Mound Systems

Mound systems are a proven alternative system that are used when a high groundwater table or impervious layer is encountered.  The three components of a mound system are a septic tank, dosing (pumping) chamber, and an elevated mound.

The dosing chamber provides:

• Dosing and resting cycles.

• Uniform distribution of effluent.

• Known level of sewage treatment in the sand fill before disposal.

• Greater distance for effluent to travel before reaching groundwater.

The fill consists of a coarse sand and minimum amount of fines that result in an acceptable treatment at an acceptable loading rate.