Exploring The Different Types of Septic Systems in Oklahoma

If you’ve had a soil profile or perk test done in Oklahoma, you may have noticed the 7 types of septic system distribution methods shown under the system design.  We often get questions about what these mean or what types of septic systems are legal in Oklahoma.  

Most of these systems require a soil test to size them properly.  The sizing takes into account the occupancy of the house and the amount of water the ground will absorb.

You will see a lot of these are simply variations of a similar design.  Keep reading to understand each type and the pros and cons of each.

(CSA) Conventional Subsurface Absorption

Conventional subsurface absorption is known by many names: leach field, lateral lines, drain field and more.  This is the type you probably think of when you hear the words ‘septic system’.  It is a subsurface distribution system.

The septic tank used will be at least 1000 gallons and can be a tank with a single compartment or divided into two compartments.  A line is then ran from the tank to the distribution area.  

The subsurface lines are excavated and either perforated pipe with gravel or a manufactured system like chambers are laid in the trenches.  The trenches are then covered.  

Grass should be the only thing planted above the lines and you should avoid driving on them.

Conventional Septic System Pros

  • Lower maintenance cost (no moving parts)
  • Can handle lower flows (less than 100 gpd) better
  • Will last 40+ years with proper maintenance
  • Low flow systems may be less expensive than other options

Conventional Septic System Cons

  • Maintenance is often ignored
  • Large footprint
  • High flow systems may be more expensive than other options

(LPD) Low Pressure Dosing

A low pressure dosing system is another subsurface distribution type of septic system.  

The pump tank is placed downstream from the septic tank and the wastewater is pumped to the distribution field in measured amounts.

While they are considered a standard system in Oklahoma, they are very rare.  In fact, the DEQ estimated in 2023 that less than 2 per year are installed in Oklahoma.  

They have made moves to have them removed as a standard system.  This should go into effect in late 2024 or early 2025 so we won’t spend much time on them.

LPD Septic System Pros

  • One of only 2 subsurface systems that can be installed in a Group 1 soil
  • Only standard option for a low flow system in Group 1 soil

LPD Septic System Cons

  • Very limited applications
  • Requires electric service and maintenance

(SE) Shallow Extended

A shallow extended septic system is almost identical to a conventional system.

As the name implies, the difference lies in how the lateral lines are installed.  They are shallower and longer than regular lateral lines.

This system is installed when you have shallow rock or another natural barrier that doesn’t allow for a conventional system.  To make up for the lack of good soil, more laterals are required. 

If you buy a home with one of these systems you will likely never know you have anything other than a regular septic unless you receive a copy of the paperwork.

SE Septic System Pros

  • Lower maintenance cost (no moving parts)
  • Can handle lower flows (less than 100 gpd)
  • Will last 40+ years with proper maintenance

SE Septic System Cons

  • Maintenance is often ignored
  • Very large footprint
  • May be more expensive than other options

(ET/A) Evapotranspiration / Absorption

Evapotranspiration.  That’s a mouthful!

In simple terms, an ETA septic system is designed to depend on evaporation in addition to absorption.  These systems are installed in heavy clay soils.

Clays swell when they absorb water.  When the clay is saturated absorption can no longer occur so you will start to have water surface or backup.  ETA’s are designed to maximize the amount of evaporation to help handle the excess water.

They do this a few ways:

  • They are installed shallower than conventional systems.  
  • They require more lateral lines
  • The soil above the laterals is mounded to maximize surface area

In the past, a lot of conventional septic systems were installed in clay soils without any changes and they have worked for the most part.  However, you’re more likely to have soggy ground above them or problems with your plumbing when it rains.

Even with newer homes that have ETA’s we find the mounded lines are removed either by the builder or homeowner.  So, if you buy a home with this type of system you may not realize it without the paperwork.

Infographic showing the differences between a conventional and evapotranspiration septic system

ETA Septic System Pros

  • Lower maintenance cost (no moving parts)
  • Can handle lower flows (less than 100 gpd)
  • Will last 40+ years with proper maintenance
  • The only standard subsurface system available for low flow systems in clay soils

ETA Septic System Cons

  • Maintenance is often ignored
  • Very large footprint
  • More expensive than other options
  • Mounds may be undesirable in yard

(L) Lagoon

Lagoons are a favorite among DEQ regulators.  They are easy to maintain and the wastewater is treated by evaporation instead of absorption so the chance of groundwater pollution is minimal.  

Once common in rural areas, lagoons are now becoming largely undesirable for homeowners.

Despite common belief, lagoons have a septic tank in front of them.  The only water going into the pond is the same water that would go into lateral lines.  If properly maintained, they should not smell.

You should plan on pumping the septic tank every 3-5 years to keep the lagoon working properly and odor free.

Lagoon Septic System Pros

  • Lower maintenance cost (no moving parts)
  • Low cost for large flow systems
  • Will last 40+ years with proper maintenance

Lagoon Septic System Cons

  • Maintenance is often ignored
  • Large footprint
  • Lagoon may be undesirable in yard
  • Neighbors may complain about the lagoon if they are unfamiliar with them
  • Cannot be used for low flows

(DI) Drip Irrigation

Aerobic drip irrigation isn’t used much in Oklahoma but it is a great option when a small footprint is needed.  

The system uses the same aerobic tank you may already be familiar with.  Instead of sending the water to spray heads, it goes to an underground drip field.

One thing that has been observed in Oklahoma is the state recommended sizes are too small.  Therefore, don’t be surprised if your installer recommends doubling the drip area.  

They aren’t doing it just to increase the cost.  They are trying to save you from a failed system.  

Drip System Pros

  • Only subsurface system that can be installed in any soil
  • Smallest footprint of any system
  • New systems include 2 yrs of warranty and maintenance

Drip System Cons

  • Highest maintenance cost
  • Most expensive system to install
  • Needs to be pumped more often due to smaller trash tank size

(SI) Spray Irrigation

An aerobic system with spray distribution is the primary choice for developers and the most common system installed in Oklahoma.

The aerobic system can be installed in a few hours with minimal disruption to your yard.

Aerobic systems can get a lot of hate but most of the issues people complain about are simply due to a lack of maintenance. Pumping the tank every 2-3 years will prevent a lot of problems.

If the sprayers smell, you should call a septic company to have the tank looked at!

Spray System Pros

  • Can be installed in any soil
  • New systems include 2 yrs of warranty and maintenance
  • Flexible footprint

Spray System Cons

  • Moderate maintenance cost
  • Needs to be pumped more often due to smaller trash tank size

Alternative Septic System

This isn’t a single type of system but you may need to submit an alternative review for your septic system project.  You will want an experienced septic installer to manage a complex project like this.

This can happen for a number of reasons with the most common being:

  • A lot smaller than the allowed size
  • A system won’t ‘fit’ into the standard designs due to soil or flow limitations

A certified septic installer should know right away if your system will need to be approved under this process.  It’s best to get the installer and profiler together to discuss the project before submitting any paperwork (or hire a company that does both like Cyclone!)

The application process can be involved and take several submissions so prepare well in advance if you believe you may need to an alternative review application.

Learn more from the OSU Extension Office.

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