Which of the following is NOT a classification for low hydraulic conductivity?

Low hydraulic conductivity refers to the rate at which water can move through soil pores. Soil texture and composition play significant roles in determining hydraulic conductivity. Generally, finer textured soils, such as clay and silt, exhibit low hydraulic conductivity due to their small particle sizes and small pore spaces, which can restrict water movement.

In the given options, the classifications C, SiC, and SC represent textures that are either clayey or have a significant amount of silt and clay, all of which are known to contribute to low hydraulic conductivity. Sandy soils, however, are composed of larger particles with larger pore spaces, allowing water to flow through them more freely. Therefore, sandy soils are typically associated with high hydraulic conductivity, making them distinct from the other mentioned textures.

Consequently, "D" serves as the correct answer as it identifies a classification that does not fit within the context of low hydraulic conductivity.