Hydrogeology and Contaminant transport

Question 1

Why are clays suitable as liner materials in landfill constructions?

Answer 1

• low hydraulic conductivity (permeability)
• ability to sorb and retain chemical compounds

Question 2

What is CEC? Why is it important for a contaminant transport in soil?

Answer 2

Cation exchange capacity – the amount of cations a soil can hold. Clay particles provide
surface for adsorption of cations (positively charged ions, metals).

Question 3

: Explain how the hydraulic gradient influences contaminant transport in soil. What happens to the contaminant spread when the hydraulic gradient is equal to 0?

Answer 3

The hydraulic gradient (i) is a loss in pressure head per distance unit in the direction of
the flow. The higher the hydraulic gradient, the higher the water and contaminant movement
(v) through the soil: v=ki.
If the hydraulic gradient equals to zero, the velocity of the water is zero. At i=0, contaminant
spread is diffusion driven.

Question 4

What types of geological materials have permeability of 10^-9 to 10^-11?

Answer 4

Clayey till. (they can also add clays)

Question 5

How were clayey tills formed?

Answer 5

• Clayey tills were formed by glacial drift deposited directly by the glacial.
• If students answered also “clay”, these were formed by slow melt of glacial as deposits
  in glacial lakes.