Hydrology of Soil Types

Group A

• Soil types in Group A allow water to transmit freely through the soil since they have a low runoff potential when thoroughly wet. These soils are usually 10 percent clay and 90 percent sand or gravel. Their textures are sandy. There can be soil type variances within Group A, such as loamy sand and silt loam, if they have more than 35 percent rock fragments. The depth of the water-impermeable layer is more than 20 inches for this group, and the depth of the water table is more than 24 inches.

Group B

• Soil types in Group B allow water to transmit through the soil unimpeded since they have a moderately low runoff potential when thoroughly wet. These soils are usually 10 to 20 percent clay, and 50 to 90 percent sand. They have loamy sand and sandy loam textures. Also, loam, silt loam, silt and sandy clay loam textures are placed in this group if they have more than 35 percent rock fragments. The depth of the water-impermeable layer in this group is greater than 20 inches, and the depth of the water table must be greater than 24 inches.

Group C

• Soil types in Group C allow water to transmit through the soil in a somewhat restricted way since they have a moderately high runoff potential. These soils are usually 20 to 40 percent clay and more than 50 percent sand, They include loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures. Also, clay, silty clay, or sandy clay textures are placed in this group if they have 35 percent rock fragments. The depth of the water impermeable layer in this group must be greater than 20 inches, and the depth of the water table must be greater than 24 inches.

Group D

• Soil types in Group D allow water to transmit through the soil in a restricted or very restricted way since they have high runoff potential when thoroughly wet. These soils are usually more than 40 percent clay and less than 50 percent sand. They have clayey textures. The depth of the water-impermeable layer in this group must be greater than 20 inches, and the depth of the water table must be greater than 24 inches.