7.2.2 Drain Fields Explained

Key Concepts

• Drain Field Function
• Types of Drain Fields
• Components of Drain Fields
• Installation Process
• Maintenance and Troubleshooting

Drain Field Function

A drain field, also known as a leach field or soil absorption system, is a critical component of a septic system. Its primary function is to disperse treated wastewater from the septic tank into the soil, where it is further filtered and purified before it reaches groundwater.

Types of Drain Fields

There are several types of drain fields, each designed to suit different soil conditions and site requirements:

• Conventional Drain Field: The most common type, consisting of trenches filled with gravel and perforated pipes.
• Chamber Drain Field: Uses plastic chambers instead of gravel to provide a larger surface area for wastewater distribution.
• Mound System: Used in areas with poor soil conditions, where the drain field is elevated above the natural ground level.
• Evapotranspiration System: Designed for arid regions, where the drain field is covered with a layer of gravel and a waterproof membrane to allow water to evaporate.

Components of Drain Fields

Key components of a drain field include:

• Perforated Distribution Pipes: Pipes with holes that allow wastewater to seep into the surrounding soil.
• Gravel or Chambers: Provides a medium for wastewater to spread out and be absorbed by the soil.
• Trenches: Channels dug into the ground to house the distribution pipes and gravel or chambers.
• Soil: Acts as a natural filter, removing contaminants from the wastewater.

Installation Process

The installation of a drain field involves several steps:

• Site Evaluation: Assess the soil type, slope, and groundwater level to determine the best location and type of drain field.
• Excavation: Dig trenches according to the design specifications.
• Pipe Laying: Install perforated pipes in the trenches, ensuring proper slope and alignment.
• Gravel or Chamber Placement: Fill the trenches with gravel or place plastic chambers around the pipes.
• Covering: Backfill the trenches with soil and cover the drain field with grass or other vegetation to prevent erosion.

Maintenance and Troubleshooting

Proper maintenance and troubleshooting are essential to ensure the longevity and effectiveness of a drain field:

• Regular Inspection: Periodically check the drain field for signs of failure, such as standing water or odors.
• Pumping the Septic Tank: Ensure the septic tank is pumped regularly to prevent solids from entering the drain field.
• Water Usage Management: Avoid excessive water usage that can overwhelm the drain field.
• Repair and Replacement: Address any issues promptly, such as repairing damaged pipes or replacing failed components.

Examples and Analogies

Think of a drain field as a "natural purification plant" where the soil acts as a filter, cleaning the water before it reaches groundwater sources. The perforated pipes are like "irrigation channels" that distribute water evenly across the field, while the gravel or chambers are like "sponges" that absorb and spread the water.

A conventional drain field can be compared to a "garden bed" where water is slowly released into the soil, allowing plants to absorb it. A mound system is like an "elevated garden" designed to overcome poor soil conditions, ensuring proper filtration.