Groundwater vulnerability also depends on pesticide properties, management practices, site conditions, and environmental factors, all of which must be evaluated to determine the actual risk of groundwater contamination. Intrinsic leaching potential is a soil's ability to transmit water independent of water availability. It is calculated using only soil permeability and depth to groundwater. Water moving through soils with high intrinsic leaching potential is more likely to carry dissolved materials, including pesticides, to groundwater. Hydraulic loading is the amount of water available at the soil surface to create leaching conditions.
Hydraulic loading depends on rainfall, irrigation, and surface runoff.
Sandy soils may have high leaching potentials, but if the only source of hydraulic loading is from rainfall in an 8-inch precipitation zone, the actual amount of leaching is extremely low. Irrigating such soils may substantially increase the actual leaching potential. Runoff decreases the amount of water that enters the soil, thus decreasing the amount of hydraulic loading available to drive chemicals toward groundwater. Soils with high runoff potentials are more likely to contribute to surface water contamination. Dryland, or nonirrigated leaching potential , corrects the intrinsic leaching potential for hydraulic loading due only to rainfall.