Careful management of the amount and timing of irrigation water applications can be very effective in reducing the risk of groundwater contamination. The position of a soil in the landscape also influences its hydraulic loading. Soils near a hilltop often shed water, either by runoff over the surface or by lateral flow within the soil. Soils lower on the hillside and where the slope begins to flatten out often receive excess water from the higher positions. These soils are more susceptible to leaching from the added hydraulic loading.
Sorption refers to the binding of chemicals to particles of organic matter and clay in the soil.
Sorption retains chemicals in the soil, where they can be degraded. Thus the higher the sorption potential, the lower the risk of groundwater contamination. Sorption potential depends on organic matter content and clay content. Organic matter content is the most important variable affecting sorption of pesticides. Organic matter provides the greatest number of binding sites because it has an extremely large surface area and is very reactive chemically.