Hydrologic Soil Group Classification

Group A Soil

• Group A soil has low runoff potential and a high infiltration rate even when wet. The group consists of soil that is deep and well-to-excessively draining. The soil ranges from sandy loam to high gravel content. The water transmission rate is greater than 0.30 inch per hour. Sandy loam in this hydrologic soil group is recommended for normal home gardening. Sandy loam garden soil forms small clumps and falls easily from the hand.

Group B Soil

• Group B hydrologic soil classification indicates silt loam or loam soil. It has moderately fine-to-moderately course texture created by its mineral particle content relative to its organic matter content. It has small amounts of sand and clay in silt-size particles. Group B soils have moderate water infiltration rates 0.15 to 0.30 inch per hour. They are moderately well-to-well-draining soils.

Group C Soil

• Group C soils have slow infiltration rates even when thoroughly wetted. They have a layer that impedes the movement of water downward. Group C hydrologic soils are moderately fine-to-fine in texture. It forms a more cohesive ball than Group B soils when squeezed in the hand. The rate of water filtration is 0.05 to 0.15 inch per hour. Garden soil of this group type benefits from adding compost increasing its water filtration rate.

Group D Soil

• Hydrologic soil classification Group D consists of soils with high clay content and very low rate of water transmission. Clay is the finest textured soil of all classifications. It forms hard clods or clumps when dry or squeezed in the hand. It is sticky and plastic when wet. Group D soils have a permanently high water table and high swelling potential. Its rate of water filtration and transmission is 0 to 0.05 inch per hour.