Why are liners laid down at the bottom of a landfill before waste in the landfill?

They don't want all the liquified crud in the landfill to sink into the ground and pollute the aquifer.

Liners are typically laid down at the bottom of a landfill before waste is dumped to serve as a protective barrier between the waste and the underlying soil and groundwater. They are critical in minimizing the potential negative impacts that landfill waste can have on the environment.

There are several reasons why liners are used:

1. Preventing groundwater contamination: One of the major concerns with landfills is the contamination of groundwater, which can occur when harmful chemicals and pollutants from the waste seep down into the groundwater table. Liners act as a barrier, preventing these substances from leaching into the surrounding soil and groundwater.

2. Controlling landfill gas migration: Landfill waste undergoes decomposition, which produces landfill gas, mainly comprised of methane and carbon dioxide. Liners help to control the migration of these gases, reducing the risk of them entering the surrounding environment and contributing to air pollution or even explosions.

3. Limiting soil contamination: By preventing direct contact between the waste and the underlying soil, liners help to minimize soil contamination. This is important because contamination of soil can have adverse effects on plant and animal life in the area surrounding the landfill.

The design of liners typically includes multiple layers, each serving a specific purpose. The most commonly used liner system consists of a combination of clay and synthetic materials such as geomembranes (plastic sheets) or geosynthetic clay liners. These layers are overlapped and sealed properly to form an impermeable barrier.

Overall, the use of liners is an essential part of modern landfill engineering, as it helps prevent or minimize the release of harmful substances into the surrounding environment, protecting both groundwater and soil from contamination.