The Water Cycle:
Just because you have a well that yields plenty of water doesn't mean you can go ahead and just take a drink. Because water is such an excellent solvent it can contain lots of dissolved chemicals. And since groundwater moves through rocks and subsurface soil, it has a lot of opportunity to dissolve substances as it moves. For that reason, groundwater will often have more dissolved substances than surface water will.
Even though the ground is an excellent mechanism for filtering out particulate matter, such as leaves, soil, and bugs, dissolved chemicals and gases can still occur in large enough concentrations in groundwater to cause problems. Undergroundwater can get contaminated from industrial, domestic, and agricultural chemicals from the surface. This includes chemicals such as pesticides and herbicides that many homeowners apply to their lawns.
Contamination of groundwater by road salt is of major concern in northern areas of the United States. Salt is spread on roads to melt ice, and, with salt being so soluble in water, excess sodium and chloride is easily transported into the subsurface groundwater. The most common water-quality problem in rural water supplies is bacterial contamination from septic tanks, which are often used in rural areas that don't have a sewage-treatment system. Effluent (overflow and leakage) from a septic tank can percolate (seep) down to the water table and maybe into a homeowner's own well. Just as with urban water supplies, chlorination may be necessary to kill the dangerous bacteria.
The U.S. Geological Survey is involved in monitoring the Nation's groundwater supplies. A national network of observation wells exists to measure regularly the water levels in wells and to investigate water quality.
Contaminants can be natural or human-induced
Naturally occurring contaminants are present in the rocks and sediments. As groundwater flows through sediments, metals such as iron and manganese are dissolved and may later be found in high concentrations in the water. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants from leaking fuel tanks or fuel or toxic chemical spills may enter the groundwater and contaminate the aquifer. Pesticides and fertilizers applied to lawns and crops can accumulate and migrate to the water table.
The physical properties of an aquifer, such as thickness, rock or sediment type, and location, play a large part in determining whether contaminants from the land surface will reach the groundwater. The risk of contamination is greater for unconfined (water-table) aquifers than for confined aquifers because they usually are nearer to land surface and lack an overlying confining layer to impede the movement of contaminants. Because groundwater moves slowly in the subsurface and many contaminants sorb to the sediments, restoration of a contaminated aquifer is difficult and may require years, decades, centuries, or even millennia.
Inorganic contaminants found in groundwater
|Contaminant||Sources to groundwater||Potential health and other effects
||Occurs naturally in some rocks and drainage from mines.
||Can precipitate out of water after treatment, causing increased turbidity or discolored water.
||Enters environment from natural weathering, industrial production, municipal
waste disposal, and manufacturing of flame retardants, ceramics, glass,
batteries, fireworks, and explosives.
||Decreases longevity, alters blood levels of glucose and cholesterol in
laboratory animals exposed at high levels over their lifetime.
|Arsenic||Enters environment from natural processes, industrial activities, pesticides, and industrial waste, smelting of copper, lead, and zinc ore.||Causes acute and chronic toxicity, liver and kidney damage; decreases blood hemoglobin. Possible carcinogen.
||Occurs naturally in some limestones, sandstones, and soils in the eastern United States.
||Can cause a variety of cardiac, gastrointestinal, and neuromuscular
with hypertension and cardiotoxicity in animals.
|Beryllium||Occurs naturally in soils, groundwater, and surface water. Often used in electrical industry
equipment and components, nuclear power and space industry. Enters the environment
from mining operations, processing plants, and improper waste disposal.
Found in low concentrations in rocks, coal, and petroleum and enters the ground and
||Causes acute and chronic toxicity; can cause damage to lungs and bones.
||Found in low concentrations in rocks, coal, and petroleum and enters the ground and
surface water when dissolved by acidic waters. May enter the environment from industrial
discharge, mining waste, metal plating, water pipes, batteries, paints and pigments,
plastic stabilizers, and landfill leachate.
||Replaces zinc biochemically in the body and causes high blood pressure,
liver and kidney
damage, and anemia. Destroys testicular tissue and red blood cells. Toxic
|Chloride||May be associated with the presence of sodium in drinking water when present in high
concentrations. Often from saltwater intrusion, mineral dissolution, industrial and
||Deteriorates plumbing, water heaters, and municipal water-works equipment
at high levels.
Above secondary maximum contaminant level, taste becomes noticeable.
|Chromium||Enters environment from old mining operations runoff and leaching into groundwater,
fossil-fuel combustion, cement-plant emissions, mineral leaching, and waste incineration.
Used in metal plating and as a cooling-tower water additive.
||Chromium III is a nutritionally essential element. Chromium VI is much
more toxic than
Chromium III and causes liver and kidney damage, internal hemorrhaging,
damage, dermatitis, and ulcers on the skin at high concentrations.
|Copper||Enters environment from metal plating, industrial and domestic waste, mining, and mineral leaching.||Can cause stomach and intestinal distress, liver and kidney damage, anemia in high
doses. Imparts an adverse taste and significant staining to clothes and fixtures. Essential
trace element but toxic to plants and algae at moderate levels.
|Cyanide||Often used in electroplating, steel processing, plastics, synthetic fabrics, and fertilizer
production; also from improper waste disposal.
||Poisoning is the result of damage to spleen, brain, and liver.
|Dissolved solids||Occur naturally but also enters environment from man-made sources such as landfill
leachate, feedlots, or sewage. A measure of the dissolved "salts" or minerals in the
water. May also include some dissolved organic compounds.
||May have an influence on the acceptability of water in general. May
be indicative of the
presence of excess concentrations of specific substances not included
in the Safe Water
Drinking Act, which would make water objectionable. High concentrations
solids shorten the life of hot water heaters.
|Fluoride||Occurs naturally or as an additive to municipal water supplies; widely used in industry.
||Decreases incidence of tooth decay but high levels can stain or mottle
teeth. Causes crippling
bone disorder (calcification of the bones and joints) at very high levels.
||Result of metallic ions dissolved in the water; reported as concentration
of calcium carbonate.
Calcium carbonate is derived from dissolved limestone or discharges from
or abandoned mines.
|Decreases the lather formation of soap and increases scale formation
in hot-water heaters
and low-pressure boilers at high levels.
||Occurs naturally as a mineral from sediment and rocks or from mining,
and corroding metal.
|Imparts a bitter astringent taste to water and a brownish color to laundered
||Enters environment from industry, mining, plumbing, gasoline, coal,
and as a water
|Affects red blood cell chemistry; delays normal physical and mental
babies and young children. Causes slight deficits in attention span, hearing,
in children. Can cause slight increase in blood pressure in some adults.
|Manganese||Occurs naturally as a mineral from sediment and rocks or from mining
and industrial waste.
||Causes aesthetic and economic damage, and imparts brownish stains to
taste of water, and causes dark brown or black stains on plumbing fixtures.
non-toxic to animals but toxic to plants at high levels.
|Mercury||Occurs as an inorganic salt and as organic mercury compounds. Enters the environment from industrial waste, mining, pesticides, coal, electrical equipment (batteries, lamps, switches), smelting, and fossil-fuel combustion.||Causes acute and chronic toxicity. Targets the kidneys and can cause nervous system disorders.
|Nickel||Occurs naturally in soils, groundwater, and surface water. Often used in electroplating, stainless steel and alloy products, mining, and refining.||Damages the heart and liver of laboratory animals exposed to large amounts over their lifetime.
|Nitrate (as nitrogen)||Occurs naturally in mineral deposits, soils, seawater, freshwater systems, the atmosphere, and biota. More stable form of combined nitrogen in oxygenated water. Found in the highest levels in groundwater under extensively developed areas. Enters the environment from fertilizer, feedlots, and sewage.||Toxicity results from the body's natural breakdown of nitrate to nitrite. Causes "bluebaby disease," or methemoglobinemia, which threatens oxygen-carrying capacity of the blood.
|Nitrite (combined nitrate/nitrite)||Enters environment from fertilizer, sewage, and human or farm-animal waste.||Toxicity results from the body's natural breakdown of nitrate to nitrite. Causes "bluebaby disease," or methemoglobinemia, which threatens oxygen-carrying capacity of the
|Selenium||Enters environment from naturally occurring geologic sources, sulfur, and coal.||Causes acute and chronic toxic effects in animals--"blind staggers" in cattle. Nutritionally essential element at low doses but toxic at high doses.
|Silver||Enters environment from ore mining and processing, product fabrication, and disposal. Often used in photography, electric and electronic equipment, sterling and electroplating, alloy, and solder. Because of great economic value of silver, recovery practices are typically used to minimize loss.||Can cause argyria, a blue-gray coloration of the skin, mucous membranes, eyes, and organs in humans and animals with chronic exposure.
|Sodium||Derived geologically from leaching of surface and underground deposits of salt and decomposition of various minerals. Human activities contribute through de-icing and washing products.||Can be a health risk factor for those individuals on a low-sodium diet.
|Sulfate||Elevated concentrations may result from saltwater intrusion, mineral dissolution, and domestic or industrial waste.||Forms hard scales on boilers and heat exchangers; can change the taste of water, and has a laxative effect in high doses.
|Thallium||Enters environment from soils; used in electronics, pharmaceuticals manufacturing, glass, and alloys.||Damages kidneys, liver, brain, and intestines in laboratory animals when given in high doses over their lifetime.
|Zinc||Found naturally in water, most frequently in areas where it is mined. Enters environment from industrial waste, metal plating, and plumbing, and is a major component of sludge.||Aids in the healing of wounds. Causes no ill health effects except in very high doses. Imparts an undesirable taste to water. Toxic to plants at high levels.
Organic contaminants found in groundwater
|Contaminant||Sources to groundwater||Potential health and other effects
|Volatile organic compounds||Enter environment when used to make plastics, dyes, rubbers, polishes, solvents, crude oil, insecticides, inks, varnishes, paints, disinfectants, gasoline products, pharmaceuticals, preservatives, spot removers, paint removers, degreasers, and many more.||Can cause cancer and liver damage, anemia, gastrointestinal disorder, skin irritation, blurred vision, exhaustion, weight loss, damage to the nervous system, and respiratory tract irritation.
|Pesticides||Enter environment as herbicides, insecticides, fungicides, rodenticides, and algicides.||Cause poisoning, headaches, dizziness, gastrointestinal disturbance, numbness, weakness, and cancer. Destroys nervous system, thyroid, reproductive system, liver, and kidneys.
|Plasticizers, chlorinated solvents, benzo[a]pyrene, and dioxin||Used as sealants, linings, solvents, pesticides, plasticizers, components of gasoline, disinfectant, and wood preservative. Enters the environment from improper waste disposal, leaching runoff, leaking storage tank, and industrial runoff.||Cause cancer. Damages nervous and reproductive systems, kidney, stomach, and liver.
Microbiological contaminants found in groundwater
|Coliform bacteria||Occur naturally in the environment from soils and plants and in the intestines of humans and other warm-blooded animals. Used as an indicator for the presence of pathogenic bacteria, viruses, and parasites from domestic sewage, animal waste, or plant or soil material.||Bacteria, viruses, and parasites can cause polio, cholera, typhoid fever, dysentery, and infectious hepatitis.
Radiological contaminants found in groundwater
|Gross alpha-particle activity||A category of radioactive isotopes. Occurs from either natural or man-made sources including weapons, nuclear reactors, atomic energy for power, medical treatment and diagnosis, mining radioactive material, and naturally occurring radioactive geologic formations. Primary concern is natural sources, which are ubiquitous in the environment (Durrance, 1986); secondary concern is man-made sources.||Damages tissues and destroys bone marrow.
|Combined radium-226 and radium-228||Enters environment from natural and man-made sources. Historical industrial-waste sites are the main man-made source.||Causes cancer by concentrating in the bone and skeletal tissue.
|Beta-particle and photon radioactivity||A category of radioactive isotopes from either natural or man-made sources including weapons, nuclear reactors, atomic energy for power, medical treatment and diagnosis, mining radioactive material, and naturally occurring radioactive geologic formations. Primary concern is man-made sources because of widespread use (Durrance, 1986); secondary concern is natural sources.||Damages tissues and destroys bone marrow.
Physical characteristics of groundwater
|Turbidity||Caused by the presence of suspended matter such as clay, silt, and fine particles of organic and inorganic matter, plankton, and other microscopic organisms. A measure how much light can filter through the water sample.||Objectionable for aesthetic reasons. Indicative of clay or other inert suspended particles in drinking water. May not adversely affect health but may cause need for additional treatment. Following rainfall, variations in groundwater turbidity may be an indicator of surface contamination.
|Color||Can be caused by decaying leaves, plants, organic matter, copper, iron, and manganese, which may be objectionable. Indicative of large amounts of organic chemicals, inadequate treatment, and high disinfection demand. Potential for production of excess amounts of disinfection byproducts.||Suggests that treatment is needed. No health concerns. Aesthetically unpleasing.
|pH||Indicates, by numerical expression, the degree to which water is alkaline or acidic. Represented
on a scale of 0-14 where 0 is the most acidic, 14 is the most alkaline, and 7 is
neutral.||High pH causes a bitter taste; water pipes and water-using appliances become encrusted;
depresses the effectiveness of the disinfection of chlorine, thereby causing the need for
additional chlorine when pH is high. Low-pH water will corrode or dissolve metals and
|Odor||Certain odors may be indicative of organic or non-organic contaminants that originate
from municipal or industrial waste discharges or from natural sources.||
|Taste||Some substances such as certain organic salts produce a taste without an odor and can be evaluated by a taste test. Many other sensations ascribed to the sense of taste actually are
odors, even though the sensation is not noticed until the material is taken into the mouth.||
Some information on this page is from Waller, Roger M., Ground Water and the Rural Homeowner, Pamphlet, U.S. Geolgoical Survey, 1982