The soil layer that perches water acts as a barrier to prevent contaminants from moving to the permanent groundwater supply. Perched water, however, is more likely to move into a surface water source, creating a concern for surface water quality. Soil survey reports contain information on water table conditions in soils. The depth to the water table, the months during which it persists, and whether it is perched or apparent all are given in tabular format. This information is very useful in assessing soil sensitivity.
Hydraulic loading refers to the total amount of water applied to the soil.
No matter how permeable the soil, the leaching potential remains low if there is insufficient water to move completely through the soil. Where rainfall exceeds both plant consumptive use and the soil's ability to store water, leaching occurs. Water moving below the root zone ultimately reaches groundwater, carrying with it soluble soil constituents. In these soils, the leaching potential is highly correlated with soil permeability. Irrigation compensates for water deficits in dry areas.