In soil texture classification, which texture would be most appropriate for an aquitard due to low permeability?

In soil texture classification, which texture would be most appropriate for an aquitard due to low permeability?

• A. SW (Well-Graded Sand)
• B. SP (Sandy)
• C. SM (Silt)
• D. CL (Clay)

Answer: (D)

The key idea is that permeability drops as soil becomes finer. An aquitard is a layer that resists groundwater flow, so you want a texture with very low hydraulic conductivity. Clay fits this best because clay minerals are extremely fine and plate-like, producing tiny pore spaces and strong attraction between particles. That combination makes water move very slowly through clay, keeping it from transmitting groundwater easily. In contrast, well-graded sand or sandy textures have much larger pores and far higher permeability, so they would not act as effective barriers. Silt is finer than sand and has lower permeability than sand, but it still conducts water more readily than clay. Therefore, among the options, clay is the texture most appropriate for an aquitard.

The key idea is that permeability drops as soil becomes finer. An aquitard is a layer that resists groundwater flow, so you want a texture with very low hydraulic conductivity. Clay fits this best because clay minerals are extremely fine and plate-like, producing tiny pore spaces and strong attraction between particles. That combination makes water move very slowly through clay, keeping it from transmitting groundwater easily.

In contrast, well-graded sand or sandy textures have much larger pores and far higher permeability, so they would not act as effective barriers. Silt is finer than sand and has lower permeability than sand, but it still conducts water more readily than clay. Therefore, among the options, clay is the texture most appropriate for an aquitard.