Aquifer An underground formation or group of formations in rocks and soils containing enough ground water to supply wells and springs.
Backflow A reverse flow in water pipes. A difference in water pressures pulls water from sources other than the well into a homes water system, for example waste water or flood water. Also called back siphonage.
Bacteria Microscopic living organisms; some are helpful and some are harmful. Good bacteria aid in pollution control by consuming and breaking down organic matter and other pollutants in septic systems, sewage, oil spills, and soils. However, bad bacteria in soil, water, or air can cause human, animal, and plant health problems.
Confining layer Layer of rock that keeps the ground water in the aquifer below it under pressure. This pressure creates springs and helps supply water to wells.
Contaminant Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health.
Cross-connection Any actual or potential connection between a drinking (potable) water supply and a source of contamination.
Heavy metals Metallic elements with high atomic weights, such as, mercury chromium cadmium, arsenic, and lead. Even at low levels these metals can damage living things. They do not break down or decompose and tend to build up in plants, animals, and people causing health concerns.
Leaching field The entire area where many materials (including contaminants) dissolve in rain, snowmelt, or irrigation water and are filtered through the soil.
Microorganisms Also called microbes. Very tiny life forms such as bacteria, algae, diatoms, parasites, plankton, and fungi. Some can cause disease.
Nitrates Plant nutrient and fertilizer that enters water supply sources from fertilizers, animal feed lots, manures, sewage, septic systems, industrial wastewaters, sanitary landfills, and garbage dumps.
Protozoa One-celled animals, usually microscopic, that are larger and more complex than bacteria. May cause disease.
Radon A colorless, odorless naturally occurring radioactive gas formed by the breakdown or decay of radium or uranium in soil or rocks like granite. Radon is fairly soluble in water, so well water may contain radon.
Radionuclides Distinct radioactive particles coming from both natural sources and human activities. Can be very long lasting as soil or water pollutants.
Recharge area The land area through or over which rainwater and other surface water soaks through the earth to replenish an aquifer, lake, stream, river, or marsh. Also called a watershed.
Saturated zone The underground area below the water table where all open spaces are filled with water. A well placed in this zone will be able to pump ground water.
Unsaturated zone The area above the ground water level or water table where soil pores are not fully saturated, although some water may be present.
Viruses Submicroscopic disease-causing organisms that grow only inside living cells.
Watershed The land area that catches rain or snow and drains it into a local water body (such as a river, stream, lake, marsh, or aquifer) and affects its flow, and the local water level. Also called a recharge area.
Water table The upper level of the saturated zone. This level varies greatly in different parts of the country and also varies seasonally depending on the amount of rain and snowmelt.
Well cap A tight-fitting, vermin-proof seal designed to prevent contaminants from flowing down inside of the well casing.
Well casing The tubular lining of a well. Also a steel or plastic pipe installed during construction to prevent collapse of the well hole.
Wellhead The top of a structure built over a well. Term also used for the source of a well or stream.