A septic drain field is a series of perforated tubes through which the liquid end products of waste treatment, i.e. the leachate, drain into a subsurface absorption area known as a leach field. A drainage field is part of a subsurface absorption system that treats sewage from homes and small businesses. The wastewater drains through a perforated pipe leading from the leach tanks to the soil absorption area (or leach field). The septic system uses naturally occurring soil bacteria to decompose the waste and turn it into harmless elements by providing a way for solid waste and excess water in the tank to be absorbed into the ground.
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| Step | Description |
|---|---|
Determine the Correct Size | To calculate the size of the leach field:
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Choose the Location | Location factors to consider include:
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Dig the Hole | The digging process involves:
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Install Perforated Pipe | The following details about the pipe are important:
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Pour Concrete | Concrete pouring involves:
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Function of the Leach Field | Key functions include:
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Materials Used | Common materials for construction:
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Types of Leach Fields
🌱 1. What Type of Field?
- Absorption Field (aka Leach Field, Drain Field, or Soil Absorption System)
- The effluent from your septic tank flows into perforated pipes laid in gravel trenches.
- It then absorbs into the soil, where microbes further treat the wastewater.
- Infiltration Field is just another name for the same setup—highlighting the process of effluent infiltrating the ground.
⚠️ In practice, these terms are interchangeable, all describing the final stage of a septic system where effluent is released into the surrounding soil for purification.
🧱 2. How It Works
- Wastewater enters the septic tank, where solids settle and are partially decomposed.
- The clarified liquid then travels to a distribution device, like a D-box, which evenly sends it to the field pipelines.
- The liquid seeps (leaches/infiltrates) through the gravel and into the soil. Root-zone microbes and soil particles complete the filtering process before it reaches groundwater.
✔️ 3. Design & Sizing Essentials
- Soil type determines how much area is needed.
- A percolation test measures how quickly water drains, guiding field size and layout.
- Soil absorption rates (gallons/day/sq ft) drive field dimension calculations.
⚠️ 4. Common Field Designs
- Gravel Trenches: Traditional filled with gravel and perforated pipe.
- Chamber Systems: Use above-ground plastic chambers instead of gravel—easier installation and larger capacity.
- Mound Systems: Built above ground when native soil is too permeable or shallow; uses pumped effluent.
- Advanced Types: Drip distribution, recirculating sand filters, aerobic units—used for challenging soil or site conditions.
✅ 5. Pros & Cons Comparison
| Field Type | Advantages | Drawbacks |
|---|---|---|
| Gravel Trenches | Simple, low-cost, widely used | Large footprint; can clog (biomat) if not maintained |
| Chamber Systems | Fewer materials, compact, easy to repair | Plastic may degrade; still large footprint |
| Mound Systems | Great for poor soils, shallow or high-water sites | Expensive, needs maintenance |
| Advanced Systems | Work on tricky sites with higher treatment needs | Higher cost, mechanical, requires power/maintenance |
🧰 6. Maintenance Tips
- Pump septic tank every 2–5 years—prevent solids from clogging the field.
- Avoid heavy traffic or plant roots over the field to prevent soil compaction and damage.
- Keep roof water and drives clear of the field to avoid flooding and saturation.
How To Build A Leach Field In Clay
If you’re building a leach field on clay soil, it’s important that you dig down at least 24 inches before installing any leach lines or drain tile because clay doesn’t allow for good drainage. You may also need to install layers of gravel or crushed stone beneath the pipes so that they drain properly.
There are many different types of septic field lines, and each serves a different purpose. The main ones are:
Septic drainfields: These lines carry wastewater from the house to the leach field, where it is treated and drained into the soil.
Waste discharge line: This pipe carries wastewater from a septic tank to a drainfield or leach pit. Waste discharge lines can be made from plastic or PVC pipe, or from concrete or clay tile.
Inflow line: Also known as an inlet line, this is the pipe that brings wastewater into your home through a junction box that’s located near your home’s foundation.
Septic systems are used to treat wastewater from homes and commercial buildings. The system uses a septic tank and a drainfield, which can be made up of gravel or crushed stone. The septic tank is underground and the drainfield is above ground. Septic systems can be used on any type of soil, but clay soils have special considerations.
Clay Soils
Clay soils are heavy and compacted, making holes for pipes difficult to dig. They also lack air pockets, which makes it difficult for roots to grow and penetrate the soil. Clay soil has poor drainage, so water tends to sit on top of the ground instead of sinking into the earth as it does in sandy soils. These characteristics make it difficult for septic systems to work well in clay soils.
Gravel Field Lines
A gravel field line consists of perforated pipe laid across an open area between two trees or shrubs in your yard or around your home. The pipe runs under the surface of your lawn but emerges above ground at both ends so you can connect it to other lines that run under your lawn surface as well as to a drainfield pipe that runs downslope toward a drywell or ejector pump pit located downhill from where water enters your home’s le
The leach field is the part of a septic system that is buried in the ground. The purpose of the leach field is to receive and filter the wastewater from your home before it enters the soil.
The leach field can be made up of several different types of lines, including:
Aerobic pipe: Aerobic pipe is made out of PVC or ABS plastic and connects the drainfield with the septic tank. Aerobic pipe has very small holes on one side and a larger hole on the other side that allows air into the pipe. Air helps aerobic bacteria break down wastewater in the drainfield, so this type of pipe must be buried below grade and not covered by any vegetation.
Aerobic drainfield: This type of drainfield allows water to seep through perforated pipes into gravel or sand beneath them at a slow rate. The aerobic drainfield uses aerobic bacteria as its primary treatment method for breaking down waste products in wastewater.
A leach field is a system of underground pipes that drains wastewater from a septic tank. The pipes are made of plastic or concrete, and are buried in the ground near the home’s foundation.
Leach fields can be as simple as one pipe running from the tank to the ground, or as complex as multiple lines that branch out from the main pipe to form an underground grid.
Septic tanks are designed to treat wastewater by allowing it to trickle down through gravel and filtering it through natural processes. This process can take up to six months before the water is safe to return back into the ground. As wastewater flows through the leach field, it seeps into cracks in the soil, where it’s absorbed into the groundwater supply.
In some cases, your local health department may require you to install a leach field if there isn’t enough topsoil to absorb all of the wastewater that would have gone into your septic system’s drainfield (a large hole dug in sandy soil). In others, you may choose a leach field as an alternative means of disposing of your household’s waste water because it reduces environmental pollution and protects groundwater supplies from contamination.
👷 Next Steps
Need help with:
- Calculating field size based on percolation test or bedroom count
- Choosing between trench, chamber, mound, or advanced system
- Understanding code requirements or permits in your area
✅ Bottom Line
“Absorption field” and “infiltration field” are just different terms for the same septic system component—the part where effluent disperses into and is treated by the soil. The design you choose—traditional trench, chamber, mound, or advanced system—depends on your soil type, local code requirements, budget, and site conditions.