How do soils affect the potential for groundwater contamination?
Soil characteristics are very important in determining 1) how a contaminant breaks down to harmless compounds; and 2) whether it leaches into groundwater. Because most breakdown occurs in the soil; there is a greater potential for groundwater contamination in areas where contaminants move quickly through the soil. Sandy soils have large “pore” spaces between individual particles, and the particles provide relatively little surface area for “sorption” or physical attachment of most contaminants. Large amounts of rainfall or excessive irrigation water can percolate through these soils, and can carry dissolved contaminants down through the soil and into groundwater. Clay soils, on the other hand, are made up of extremely small particles that slow the movement of water and dissolved contaminants through the soil. Contaminants also stick tightly to clay surfaces. Even with clay soils, movement of water may be through rather large cracks (preferential flow) and treatment may be questionable.
