Why are liners laid down at the bottom of a landfill before waste is deposited in the landfill ?
It's probably an attempt to keep toxic stuff from seeping into the ground ... and thus into any ground water.
Liners are laid down at the bottom of a landfill before waste is deposited to prevent harmful pollutants and contaminants from seeping into the surrounding soil and groundwater. The main purpose of the liner is to create a barrier that prevents the waste from directly contacting and polluting the natural environment.
To understand why liners are necessary, we need to consider the composition of landfills. Landfills consist of various types of waste, including household garbage, industrial waste, and construction debris, which can contain hazardous substances. Over time, these substances may leach out and migrate into the ground, potentially contaminating soil and groundwater, which are sources of drinking water for many communities.
The liner system typically consists of multiple layers, each with a specific function:
1. Compacted Clay Liner: The bottom layer is made of compacted clay, which is a low-permeability material. This clay liner acts as a primary barrier, reducing the flow of leachate (liquid that forms from waste decomposition) into the underlying soil and groundwater.
2. Synthetic Liner (usually made of plastic): Above the clay liner, a synthetic liner is placed, acting as a secondary barrier. It is usually made of materials such as high-density polyethylene (HDPE) or similar plastics. This liner enhances the impermeability and durability of the system, providing an additional defense against leachate leakage.
3. Geotextile Fabric: A geotextile fabric is often placed between the clay liner and the synthetic liner to prevent any potential damage to the latter and provide a protective cushioning layer.
4. Leachate Collection System: At the base of the landfill, a network of pipes and drains is installed to collect the leachate that accumulates in the bottom liner system. The collected leachate is then transported to a treatment facility to remove contaminants before being discharged.
In addition to liners, modern landfills also employ other engineering controls, such as daily soil cover, gas collection systems, and groundwater monitoring wells, to further safeguard the environment.
To summarize, liners are laid down at the bottom of a landfill before waste deposition to prevent the migration of pollutants into the soil and groundwater. These liners form a multi-layer barrier system that minimizes the environmental impact of the landfill.