An aquifer is a layer of sand, gravel, soil, or rock that is saturated, meaning all pore spaces are filled with water, and able to transmit groundwater in sufficient quantities for uses such as drinking water and irrigation. Groundwater does not continually dilute contaminants that reach it. Flushing a plume of contamination from groundwater may take many years. Hence, there is very little, if any, breakdown of pesticides once they reach an aquifer. When aquifers are relied upon as a source of drinking water, any pesticide contamination can be devastating.
For more information, refer to The Problem of Leaching and Glossary of Surface and Groundwater Terms from the Pesticide Environmental Stewardship website.
