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Common Contaminants

The Illinois Department of Public Health (IDPH) and the Illinois EPA recommend testing your well at least once a year for coliform bacteria and nitrates. It is also recommended to test for VOCs, if you live in an urban or suburban area with a business, industry or gas station nearby, or if you are in a rural area that may be affected by leaking fuel tanks. VOCs are capable of traveling long distances in groundwater and can persist for a long time. They also have the potential to cause adverse health effects. You may also want to consider testing for pesticides if they have been mixed, loaded or stored close to your well, especially if you have a sand point well or a large diameter dug or bored well. Consult your local health department regarding testing frequency for VOCs and pesticides.

A homeowner sampling for nitrate from an outside spigot.

Coliform Bacteria

Coliform bacteria are a group of several bacterial species that live naturally in the intestinal tracts of humans and animals. Some types of coliform bacteria also live naturally in soil and surface water. Coliform bacteria are used as a standard for bacterial quality in drinking water, as their presence in groundwater indicates sewage or surface water is entering and contaminating the water supply. Bacteria are common in the environment and generally are not harmful; however, some types can cause serious illness. Moreover, it is likely other harmful germs are present if the result is positive.

Additional information is available on the web:


This pollutant may be found at elevated levels due to nearby septic systems, manure storage areas, feedlots or farm fields. Wells vulnerable to nitrate contamination include shallow sand point wells and large diameter dug or bored wells, and wells with damaged, leaking casing or fittings. It is especially important that mothers-to-be and infants less than 6 months old are cautious about their drinking and cooking water because too much nitrate in drinking water can cause blue baby syndrome in infants, which is a result of the blood not being able to transport oxygen, causing asphyxiation. Although nitrate occurs naturally in soil and water and low levels are not toxic, nitrate can be harmful especially to babies when water levels are greater than 10 milligrams per liter. Testing for nitrate should be done at least once a year or more often if an infant or a pregnant woman is in the household. Nitrate levels may indicate that your well is vulnerable to other contaminants, including pesticides.

The following web sites contain additional information:

Pesticides, Herbicides and other Synthetic Organic Chemicals (SOCs)

These manufactured chemicals do not occur naturally, and are widely used on farmland throughout Illinois. The majority of SOCs are made up of pesticides, herbicides and insecticides, while others are used as plasticizers, wood preservatives, flame retardants, and solvents, and produced as by-products or waste materials. Some man-made chemicals are undetectable through sight and smell; however, certain aromatic chemicals, such as those in coal tar, have a very noticeable odor. Testing your drinking water is the only way to know for sure if your water is safe, especially if you live near farmland where pesticides are applied. Being aware of any farming activities that occur near your well, such as learning the specific chemicals being used, can narrow the range of chemicals to be tested.

More information is available on the web at the following sites:

  • Alachlor and atrazine are two herbicides that are widely used on corn and soybean fields for controlling grasses and broadleaf weeds. IDPH offers an online fact sheet, Alachlor and Atrazine in Groundwater
  • University of Illinois at Urbana-Champaign Cooperative Extension Service fact sheet, Pesticides and Groundwater: Pesticides as Potential Pollutants
  • The following report and contaminant specific fact sheets provide more detailed information regarding man-made chemicals and pesticides:

Volatile Organic Chemicals (VOCs): fuels (e.g., gasoline and diesel fuel) and solvents

VOCs are man-made substances that tend to evaporate or break down easily in surface water, but they can persist for many years in groundwater and can travel long distances from where they were spilled or dumped. They also can have a variety of potential health effects. These chemicals are commonly used as solvents, degreasers, dry-cleaning chemicals, and as octane enhancers in gasoline. Although these substances evaporate readily, they can enter the body through ingestion, inhalation and skin absorption as well as ingestion. Some VOCs have a chemical, fuel or fruity odor and may taste bitter, but many man-made chemicals can go unnoticed. Most VOCs do not have any detectable taste or smell; therefore testing is the only way of knowing for sure if they are present in your drinking water. Please note: if you are collecting your own sample for a VOC test, it is imperative to remove the faucet aerator prior to collecting your sample. See the general procedures for collecting water samples for VOC testing fact sheet for more information. ( Procedimiento general para recoger muestras de agua para hacerles la prueba de químicos orgánicos volátiles)

More information is available at the following web sites:

For more detailed information regarding VOCs, visit the following web sites:

The following list contains VOCs that are commonly tested for by public water supplies and can be used as a guide for testing private well water in Illinois. Please note that this list provides general guidance and is not meant to be an all inclusive parameter list.

Constituent Standard (ug/L)
Benzene* 5
Dichloromethane* 5
ortho-Dichlorobenzene 600
para-Dichlorobenzene 75
1,2-Dichloroethane* 5
1,1-Dichloroethylene 7
cis-1,2-Dichloroethylene 70
trans-1,2-Dichloroethylene 100
1,2-Dichloropropane* 5
Ethylbenzene 700
Methyl Tertiary-Butyl Ether 70
Monochlorobenzene 100
Styrene 100
Tetrachloroethylene* 5
Toluene 1000
1,1,1-Trichloroethane 200
1,1,2-Trichloroethane 5
1,2,4-Trichlorobenzene 70
Trichloroethylene* 5
Vinyl Chloride* 2
Xylenes 10000
*Denotes a carcinogen