Soil Characteristics Depth Depth to groundwater is important primarily because it determines the volume of soil through which a contaminant must travel before reaching an aquifer. It also determines the amount of time that a contaminant is in contact with the soil. Where the soil is fairly deep, the processes of filtration, sorption, biodegradation, and volatilization operate effectively. The pollution potential increases where the soils are thin and the underlying bedrock is permeable, or where the water table is near the surface. Texture influences the movement of water through a soil by its effect on size of pores and total surface area.
Sandy soils have large pores and low surface areas, allowing water to drain rapidly.
Rapid leaching of some potential groundwater pollutants may result. The sandhills region is characterized by soils of sandy texture. Clay particles provide a vast surface area on which sorption can take place. Most of the piedmont region is characterized by soils with clay subsoils. The influence of soil texture on the leaching of three popular herbicides is shown in Figure 3 .