Leach Field Design For Clay Soil

This post may contain affiliate links. This means I will make a commission at no extra cost to you should you click through and make a purchase. Read the Affiliate Disclaimer and Privacy Policy.


At first glance, clay soil may seem like an unfavorable environment for a leach field. However, with the right design and maintenance practices, a leach field can work efficiently and effectively in clay soil. In this article, we’ll explore the unique challenges of leach fields in clay soils and provide insights on how to optimize their performance.

What Is A Leach Field

A leach field, also known as a drain field, is an essential component of a septic system. It comprises a network of perforated pipes that are buried underground, adjacent to the septic tank. The leach field plays a critical role in the wastewater treatment process, which involves the natural breakdown of organic matter and the removal of contaminants from the water before it is released into the environment.

The perforations in the leach field pipes allow the partially treated effluent from the septic tank to seep through the pipes and into the surrounding gravel, where it is further treated by the soil and microorganisms. The soil acts as a natural filter, removing contaminants and bacteria from the effluent as it passes through the gravel and into the ground. The microorganisms present in the soil break down any remaining organic matter and further purify the effluent. By the time the water reaches the groundwater or surface water, it is generally safe for the environment.

Leach Field Design For Clay Soil: Understanding Clay Soils

Leach Field Design For Clay Soil

Clay soils are known for their high water retention capabilities, which can make them challenging to work with in certain situations. When it comes to designing leach fields for septic systems, understanding the properties of clay soils is crucial for ensuring the system functions effectively and sustainably over time. The two main types of clay soils are:

1. Kaolinite Clay

One type of clay soil that is well-suited for conventional septic systems is kaolinite clay. With a chemical formula of Al2Si2O5(OH)4, this type of clay has a low shrink-swell ability, which means it doesn’t expand and contract significantly in response to changes in moisture levels. This makes it less prone to cracking and shifting, which can cause issues with leach field performance.

Related Post  What Type Of Soil Is Best For A Septic Tank?

2. Montmorillonite Clay

On the other hand, montmorillonite clay soil can be problematic for leach field design. This type of clay has a high shrink-swell ability and can expand up to 150 times its size when wet, which can cause significant damage to septic systems. In addition to its high shrink-swell ability, another major drawback of montmorillonite clay is its tendency to contract when it dries out. This can exert a significant amount of strain on concrete septic systems, causing them to crack and crumble over time. Even plastic septic systems are not immune to the effects of montmorillonite clay, as they may buckle or cave in under the constant pressure of the expanding and contracting soil. As a result, it’s generally not recommended for use in leach fields.

When designing a leach field for clay soils, it’s important to take several factors into consideration, including the soil’s texture, structure, and drainage capabilities. Working with a qualified septic system designer or installer (+1 877-851-7125) can help ensure that the leach field is designed to accommodate the unique properties of the soil and that the system will function effectively and sustainably over time.

Overall, understanding the properties of clay soils is essential for effective leach field design. By choosing the right type of clay soil and designing the system appropriately, homeowners can ensure their septic systems function effectively and avoid costly repairs or replacements down the line.

Leach Field Design For Clay Soil: Septic System

Leach Field Design For Clay Soil

The type of septic system that works best for kaolinite clay soil is one that can effectively filter and treat wastewater while still allowing for proper drainage. In general, there are two main types of septic systems that are suitable for clay soil:

  1. Conventional Septic Systems Conventional septic systems, also known as gravity-fed systems, are the most common type of septic system. These systems use a septic tank to separate solid waste from wastewater. The wastewater then flows through a series of perforated pipes in the leach field, where it is filtered and treated by the soil. While conventional septic systems can work well in kaolinite clay soil, they may require more maintenance and monitoring to ensure proper drainage and prevent clogging.
  2. Alternative Septic Systems are designed to address specific issues with conventional septic systems, such as poor drainage or soil conditions. These systems use advanced treatment technologies to filter and treat wastewater before it enters the leach field. Some of the most common alternative septic systems for clay soil include:
  • Aerobic Treatment Units (ATUs): ATUs use aeration to break down organic matter and remove pathogens from wastewater before it is discharged into the leach field. These systems are often used in areas where soil conditions are poor, and drainage is a concern.
  • Mound Septic Systems, which elevate the leach field above the ground level to facilitate better drainage and reduce soil saturation.
  • Peat Filter Systems: Peat filter systems use layers of peat moss to filter and treat wastewater. These systems are ideal for areas with poor soil conditions and high levels of nitrogen.
Related Post  Septic Systems In Clay Soils

Each type of septic system has its advantages and disadvantages. The best option for your specific needs will depend on several factors, including soil conditions, site characteristics, and budget.

Designing Leach Field for Clay Soil

Proper leach field design is crucial for ensuring the effective and efficient performance of a septic system in clay soil. When designing a leach field for clay soil, there are several factors that need to be considered, including:

Soil Characteristics

The type of soil in the leach field area, including texture, permeability, and compaction, will play a significant role in the design and performance of the leach field.

Leach Field Design For Clay Soil: Site Characteristics

The topography, slope, and location of the leach field area will also need to be taken into consideration when designing a leach field in clay soil.

Size of Leach Field

The size of the leach field will depend on several factors. These include the number of bedrooms in the home, the size of the septic tank, and the soil characteristics. If the leach field is located in clay soil, it may need to be larger than if it were in a more porous soil type. This is because the slow percolation rate of clay soil can limit the ability of the effluent to be absorbed and treated by the soil.

A larger leach field can help to compensate for the reduced percolation rate. This is because it allows effluent to be distributed more evenly and provides more area for absorption. It’s important to work with a licensed professional to determine the appropriate size for a leach field in clay soils, as it will depend on a variety of factors, including soil characteristics, system design, and local regulations.

Related Post  What Type Of Soil Is Best For A Septic Tank?

Depth of Leach Field

The depth of the leach field will depend on several factors, including the depth of the water table, the soil characteristics, and local regulations.

Maximum Slope for Leach Field

The maximum slope for a leach field in clay soil is typically around 20%, but this can vary depending on local regulations and site conditions.

By taking these factors into consideration, a properly designed leach field can effectively treat and filter wastewater in clay soil while still allowing for proper drainage and preventing clogging.

Leach Field Design For Clay Soil: Montmorillonite Clay

If you have Montmorillonite clay soil and are in need of a septic system, it is recommended that you explore alternative options such as a municipal sewer or a cesspool. A municipal sewer system is a network of pipes that connect your home to a central sewage treatment facility.

A cesspool, on the other hand, is a large underground container that collects and stores wastewater. While this option can be less expensive than a municipal sewer system, it requires more maintenance and may need to be emptied more frequently.

To sum up, if you have Montmorillonite clay soil and are in need of a septic system, it is important to explore alternative options to ensure the safety and effectiveness of your wastewater treatment. Consult with a qualified professional to determine the best solution for your specific needs and circumstances.


In conclusion, designing and installing a septic system in clay soil requires careful consideration of factors such as drainage, absorption rates, and soil structure. Consulting with a professional septic system installer can provide valuable guidance and expertise in designing and installing a proper septic system. It’s important to choose the appropriate septic system and installation techniques to ensure optimal performance and long-term cost-effectiveness.