Current Groundwater Standards

Acetochlor

The groundwater standards for acetochlor were adopted in Cycle 9 (2010).

• Enforcement standard = 7 µg/L
• Preventive action limit = 0.7 µg/L

Acetochlor is a pesticide used to control weeds in corn. Animal studies show that acetochlor can affect the nose, lungs, liver, kidneys, brain, and reproductive organs.

Acetochlor ESA and OXA

The groundwater standards for acetochlor ESA and OXA were adopted in Cycle 9 (2010).

• Enforcement standard = 230 µg/L
• Preventive action limit = 46 µg/L

Acetochlor ethane sulfonic acid (ESA) and acetochlor oxanilic acid (OXA) are breakdown products of the pesticide, acetochlor. Animal studies have shown that to acetochlor ESA and OXA can affect thyroid hormones and body weight.

Acetone

The groundwater standards for acetone were adopted in Cycle 5 (1994) and updated in Cycle 9 (2010).

• Enforcement standard = 9 mg/L
• Preventive action limit = 1.8 mg/L

Acetone is an industrial solvent that is both naturally occurring and manufactured to make plastic, fibers, drugs, and other chemicals. Acetone is also found in home products, such as nail polish and varnish remover. Animal studies have shown that acetone can cause kidney, liver, and nerve damage, birth defects, and affect reproductive organs.

Alachlor

The groundwater standards for alachlor were adopted in Cycle 2 (1988) and updated in Cycle 5 (1994).

• Enforcement standard = 2 µg/L
• Preventive action limit = 0.2 µg/L

Alachlor is a pesticide used for weed control in a variety of agricultural crops including corn, soybeans, and woody ornaments. Animal studies have shown that alachlor can affect the kidneys, spleen, blood, and offspring development.

Alachlor ESA

The groundwater standards for alachlor ESA were recommended in Cycle 8 (2006) and adopted in Cycle 9 (2010).

• Enforcement standard = 20 µg/L
• Preventive action limit = 4 µg/L

Alachlor ESA is the breakdown product of the pesticide alachlor. Animal studies have shown that alachlor ESA can affect physical appearance, body weight, blood, reproductive organs, and cause lesions to the eye.

Aldicarb

The groundwater standards for aldicarb were recommended in Cycle 1 (1985).

• Enforcement standard = 10 µg/L
• Preventive action limit = 2 µg/L

Aldicarb is a pesticide used to control insects in potato crops. Animal studies have shown that aldicarb can affect neurotransmitter levels, weight gain, and cause deaths at high levels.

Aluminum

The groundwater standards for aluminum were adopted in Cycle 9 (2010) and reviewed as part of Cycle 10.

• Enforcement standard = 200 µg/L
• Preventive action limit = 40 µg/L

Aluminum is a naturally occurring metal that is used in a variety of industrial and commercial applications including cookware, food containers, and water treatment. Animal studies have shown that aluminum can affect reproductive organs, brain, and kidney function. Certain groups may be at a greater risk for aluminum toxicity such as infants and people with impaired kidney function.

Ammonia

The groundwater standards for ammonia were adopted in Cycle 9 (2010).

• Enforcement standard = 9.7 mg/L
• Preventive action limit = 0.97 mg/L

Ammonia is a naturally occurring substance that is common in nature and has agricultural, industrial, and commercial applications such as fertilizers, refrigeration systems, household cleaners, and manufacturing processes. Animal studies have shown that ammonia can affect the bones, increase blood pressure, and reduce body weight.

Anthracene

The groundwater standards for anthracene were adopted in Cycle 7 (1999).

• Enforcement standard = 3,000 µg/L
• Preventive action limit = 600 µg/L

Anthracene is a polycyclic aromatic hydrocarbon (PAH). It is used in the production of dyes and its oil is used to dilute wood preservatives. Human exposure will occur mainly through ingestion of contaminated food and water and from smoking tobacco products and inhaling polluted air. Animal studies have also shown that PAHs can affect the skin, body fluids, and immune system.

Antimony

The groundwater standards for antimony were adopted in Cycle 6 (1995).

• Enforcement standard = 6 µg/L
• Preventive action limit = 1.2 µg/L

Antimony is a metal that is used as an alloy with lead and other metals and used in the manufacturing of semiconductor devices and fire retardant chemicals. Antimony can have beneficial effects when used for medical reasons. However, animal studies have shown that high levels of antimony can affect the liver, blood sugar, and development. Human exposure has suggested that antimony exposure can affect the heart.

Arsenic

The groundwater standards for arsenic were adopted in Cycle 1 (1985) and updated in 2003.

• Enforcement standard = 10 µg/L
• Preventive action limit = 1 µg/L

Arsenic is a naturally occurring mineral that is used make other metals, glass, electronics, and wood preservatives. Additionally, some commercial pesticides contain arsenic. Studies among people have shown that exposure to high levels of arsenic for years may increase risk of certain types of cancer, affect the skin and nails, and impact the nervous system.

Asbestos

The groundwater standards for asbestos were adopted in Cycle 5 (1994).

• Enforcement standard = 7 million fibers per liter (MFL)
• Preventive action limit = 0.7 MFL

Asbestos is a group of minerals that occur naturally in the environment. They have been used in building materials, vehicle components, heat-resistant fabrics, packaging, and coatings. While the biggest health concerns come from breathing asbestos, studies among people have shown that drinking water with high levels of asbestos may increase the risk for certain types of cancer.

Atrazine

The groundwater standards for atrazine were adopted in Cycle 2 (1988) and updated in Cycle 4 (1992). These standards apply to atrazine, 2−chloro−4−amino−6−isopropylamino−s−triazine (formerly deethylatrazine), 2−chloro−4−amino−6−ethylamino−s−triazine (formerly deisopropylatrazine), and 2−chloro−4,6−diamino−s−triazine (formerly diaminoatrazine) combined.

• Enforcement standard = 3 µg/L
• Preventive action limit = 0.3 µg/L

Atrazine is a herbicide used for control of weeds in agricultural crops. Animal studies have shown that atrazine can damage the liver, kidney, and heart.

Bacteria (total coliform)

The groundwater standards for bacteria (total coliform) was first adopted in Cycle 1 (1985), updated in Cycle 6 (1995), and reviewed as part of Cycle 10.

• Enforcement standard = 0 colony forming units (CFU)
• Preventive action limit = 0 CFU

Coliforms are a group of bacteria that are naturally present in the environment. They are used to indicate the possible presence of microbial pathogens in groundwater. Pathogens in drinking water can lead to flu-like symptoms (diarrhea, nausea, vomiting, fever). Young children, the elderly, and people with weakened immune systems are more likely to be impacted than others.

Barium

The groundwater standards for barium was first adopted in Cycle 1 (1985), updated in Cycle 5 (1994), and reviewed as part of Cycle 10.

• Enforcement standard = 2 mg/L
• Preventive action limit = 0.4 mg/L

Barium is a naturally occurring metal found in many types of rock. Barium can also get into the environment from power plants and vehicle paints and from drilling mud. Studies among people have shown that barium may cause gastrointestinal disturbances and muscular weakness.

Bentazon

The groundwater standards for bentazon were adopted in Cycle 7 (1999).

• Enforcement standard = 300 µg/L
• Preventive action limit = 60 µg/L

Bentazon is a pesticide used to control weeds in a variety of agricultural crops. Animal studies have shown that bentazon can affect the intestinal tract and blood, and alter body and organ weight.

Benzene

The groundwater standards for benzene were adopted in Cycle 1 (1985). The enforcement standard was updated in Cycle 3 (1990) and in Cycle 5 (1994).

• Enforcement standard = 5 µg/L
• Preventive action limit = 0.5 µg/L

Benzene is a widely used industrial chemical that evaporates quickly and is flammable. Benzene is found in crude oil and is a major part of gasoline. It is used to make plastics, resins, synthetic fibers, rubber lubricants, dyes, detergents, drugs and pesticides. Animals studies have shown that exposure to benzene can affect bone marrow and can cause anemia (low red blood cells). Studies among people have shown that high levels of benzene exposure can cause vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate, and death.

Benzo[b]fluoranthene

The groundwater standards for benzo[b]fluoranthene were adopted in Cycle 7 (1999).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Benzo[b]fluoranthene is a polycyclic aromatic hydrocarbon (PAH) that is formed when fossil fuels, wood, or other organic material is burned. Animal studies have also shown that PAHs can affect the skin, body fluids, and immune system.

Benzo[a]pyrene

The groundwater standards for benzo[a]pyrene were adopted in Cycle 4 (1992) and updated in Cycle 6 (1995).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Benzo[a]pyrene is a polycyclic aromatic hydrocarbon (PAH) that is formed when fossil fuels, wood, or other organic material is burned. Animal studies have also shown that PAHs can affect the skin, body fluids, and immune system.

Beryllium

The groundwater standards for beryllium were adopted in Cycle 6 (1995).

• Enforcement standard = 4 µg/L
• Preventive action limit = 0.4 µg/L

Beryllium is a metal naturally found in mineral rocks, coal, and soil. Beryllium compounds are commercially mined and used in applications ranging from x-ray machines to bicycle frames to dental implants. Animal studies have shown that beryllium can cause ulcers and affect development.

Boron

The groundwater standards for boron were adopted in Cycle 7 (1999), updated in Cycle 9 (2010), and reviewed as part of Cycle 10.

Enforcement standard = 1,000 µg/L Preventive action limit = 200 µg/L

Boron is commonly found in soil and rocks. Boron compounds are used in glass production, and the manufacturing of leather tanners, fire-retardant materials, cosmetics, and photographic materials. Additionally, boron can be used in some pesticides to control cockroaches and preserve wood. Recent studies in people suggest that small amounts of boron in the diet have beneficial effects. However, animal studies have shown that large amounts of boron can affect reproduction and development. Human exposure to large amounts of boron can affect the stomach, intestines, liver, kidney, and brain.

Bromodichloromethane

The groundwater standards for bromodichloromethane were adopted in Cycle 3 (1990) and updated in Cycle 6 (1995).

• Enforcement standard = 0.6 µg/L
• Preventive action limit = 0.06 µg/L

Bromodichloromethane is a liquid that quickly evaporates into air. Most bromodichloromethane is formed during the disinfection of drinking water. Animal studies have shown that high levels of bromodichloromethane can damage the liver and kidneys, decrease immune response, and increase miscarriages.

Bromoform

The groundwater standards for bromoform were adopted in Cycle 4 (1992).

• Enforcement standard = 4.4 µg/L
• Preventive action limit = 0.44 µg/L

Bromoform is a liquid that is formed during the disinfection of drinking water. Animal studies have shown that high levels of bromoform can damage the liver, kidneys, and brain.

Bromomethane

The groundwater standards for bromomethane were adopted in Cycle 6 (1995).

• Enforcement standard = 10 µg/L
• Preventive action limit = 1 µg/L

Bromomethane is a gas that is used to make other chemicals. It has historically been used as a pesticide. While the biggest health concerns come from breathing bromomethane, animal studies have shown that ingesting high levels of bromomethane may damage the stomach.

Butylate

The groundwater standards for butylate were adopted in Cycle 2 (1988) and updated in Cycle 8 (2006).

• Enforcement standard = 400 µg/L
• Preventive action limit = 80 µg/L

Butylate is a herbicide used on corn to control weeds. When used, butylate is commonly formulated with atrazine and/or cyanazine. Animal studies have shown that butylate can affect the liver, blood, thyroid, kidneys, and body weight.

Cadmium

The groundwater standards for cadmium were adopted in Cycle 1 (1985) and updated in Cycle 3 (1990).

• Enforcement standard = 5 µg/L
• Preventive action limit = 0.5 µg/L

Cadmium is a naturally occurring metal that is used in metal plating, rechargeable batteries, paint pigments, and plastics and produced as a byproduct of zinc, lead, and copper refining. Short-term exposure to high levels of cadmium can cause stomach irritation. Long-term exposure to lower levels can cause kidney damage.

Carbaryl

The groundwater standards for carbaryl were adopted in Cycle 3 (1990) and updated in Cycle 9 (2010).

• Enforcement standard = 40 µg/L
• Preventive action limit = 4 µg/L

Carbaryl is a pesticide used to control a variety of outdoor insects. Animal studies have shown that exposure to carbaryl can increase risk of kidney and liver damage and exposure to carbaryl during pregnancy can affect survival, body weight, brain development, and bone formation in developing offspring.

Carbofuran

The groundwater standards for carbofuran were adopted in Cycle 1 (1985) and updated in Cycle 3 (1990).

• Enforcement standard = 40 µg/L
• Preventive action limit = 8 µg/L

Carbofuran is a pesticide used to control a variety of outdoor insects. Animal studies have shown that exposure to carbofuran can affect the nervous system and reproduction.

Carbon disulfide

The groundwater standards for carbon disulfide were adopted in Cycle 7 (1999).

• Enforcement standard = 1000 µg/L
• Preventive action limit = 200 µg/L

Carbon disulfide is a liquid used to make industrial chemicals. Animal studies have shown that high levels of carbon disulfide can damage the liver and heart and affect behavior. Reproductive studies in animals have shown that high levels of carbon disulfide can cause birth defects and lead to newborn death.

Carbon tetrachloride

The groundwater standards for carbon tetrachloride were adopted in Cycle 3 (1990).

• Enforcement standard = 5 µg/L
• Preventive action limit = 0.5 µg/L

Carbon tetrachloride (carbon tet) is a liquid that has historically been used a cleaning fluid in homes and industries, fire extinguishers, and grain fumigant. Carbon tet is still used to manufacture propellants and other chemicals. Studies among people have shown that exposure to high levels of carbon tetrachloride can cause nerve damage, digestive disorders, weight loss, tiredness, confusion, depression, loss of color vision and liver damage.

Chloramben

The groundwater standards for chloramben were adopted in Cycle 3 (1990).

• Enforcement standard = 150 µg/L
• Preventive action limit = 30 µg/L

Chloramben is a herbicide used to control weeds in a variety of vegetable crops, field corn, and peanuts. Animal studies have shown that high levels of chloramben can affect the liver.

Chlordane

The groundwater standards for chlordane were adopted in Cycle 5 (1994).

• Enforcement standard = 2 µg/L
• Preventive action limit = 0.2 µg/L

Chlordane is a man-made chemical that has historically been used as a pesticide, but was banned by the EPA in 1988. Animal and people studies have shown that chlordane can affect the nervous system, digestive system, and the liver. Additional animal studies have shown chlordane can cause behavioral effects in newborns when exposed before birth or while nursing.

Chlorodifluoromethane

The groundwater standards for chlorodifluoromethane were adopted in Cycle 9 (2010).

• Enforcement standard = 7 mg/L
• Preventive action limit = 0.7 mg/L

Chlorodifluoromethane is a type of Freon gas. Before the 1970s, it was used as coolant in refrigeration and air conditioning. Animal studies have shown that high levels of chlorodifluoromethane can affect kidney weight, adrenal gland weight, pituitary gland weight, and cause eye deformities in unborn rats.

Chloroethane

The groundwater standards for chloroethane were adopted in Cycle 4 (1992).

• Enforcement standard = 400 µg/L
• Preventive action limit = 80 µg/L

Chloroethane is a gas used in the production of cellulose, dyes, medicinal drugs, and other commercial products, and as a solvent and refrigerant and was historically used in leaded gasoline. Animal studies have shown that long-term exposure can cause developmental delays in unborn mice during pregnancy and uterine cancer in female rats. Chloroethane can cause muscle coordination and unconsciousness, stomach cramps, nausea, vomiting, and eye irritation.

Chloroform

The groundwater standards for chloroform were adopted in Cycle 3 (1990).

• Enforcement standard = 6 µg/L
• Preventive action limit = 0.6 µg/L

Chloroform is a liquid that is a member of a group of chemicals called "trihalomethanes." It is used to make coolants, as a fumigant for grain, and as a dry cleaning spot remover. Chloroform can be formed during the breakdown of chlorine-containing compounds and may be found in small amounts in chlorinated drinking or swimming pool water. Animal studies have shown that chloroform can cause liver and kidney tumors.

Chloromethane

The groundwater standards for chloromethane were adopted in Cycle 6 (1995) and updated in Cycle 9 (2010).

• Enforcement standard = 30 µg/L
• Preventive action limit = 3 µg/L

Chloromethane (methyl chloride) is a gas that is given off when certain materials are burned. It is also found in cigarette smoke, polystyrene insulation, aerosol propellants, and chlorinated water. The biggest health concerns come from breathing chloromethane. Animal studies have shown that chloromethane can also affect growth, damage the brain, and reduce male fertility. Studies among people have shown that long-term exposure to chloromethane in air can affect the liver, kidneys, heart rate, and blood pressure.

Chlorpyrifos

The groundwater standards for chlorpyrifos were adopted in Cycle 9 (2010).

• Enforcement standard = 2 µg/L
• Preventive action limit = 0.4 µg/L

Chlorpyrifos is a pesticide that has been widely used to control cockroaches, fleas, termites, and ticks in houses and on farms. Studies among people have shown that high levels of chlorpyrifos exposure can cause severe sweating and muscle tremors, loss of bowel control, seizures, and affect behavior.

Chromium

The groundwater standards for total chromium were adopted in Cycle 1 (1985) and updated in Cycle 5 (1994). DHS recommended standalone standards for hexavalent chromium as part of Cycle 10.

• Enforcement standard = 100 µg/L
• Preventive action limit = 10 µg/L

Chromium is a naturally occurring metal that is used in stainless steel production, pigment, manufacturing, metal finishing, leather tanning, and wood preservation. It can exist in many forms in the environment. Hexavalent chromium is the most toxic form of chromium. Animal studies show that hexavalent chromium can affect the immune system, reduce male reproduction, and damage unborn babies. Studies among people have shown that hexavalent chromium can cause liver and kidney damage.

Chrysene

The groundwater standards for chrysene were adopted in Cycle 7 (1999).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Chrysene is a polycyclic aromatic hydrocarbon (PAH) that is formed when fossil fuels, wood, or other organic material is burned. Animal studies have also shown that PAHs can affect the skin, body fluids, and immune system.

Cobalt

The groundwater standards for cobalt were adopted in Cycle 7 (1999) and reviewed as part of Cycle 10.

• Enforcement standard = 40 µg/L
• Preventive action limit = 8 µg/L

Cobalt is a naturally occurring element that is used to produce alloys and color glass, ceramics and paints. Small amounts of cobalt are found in the vitamin B12. Animal studies have shown that cobalt can affect the liver and kidneys and cause birth defects. Studies among people have shown that high levels of cobalt can affect the lungs, heart, and skin.

Copper

The groundwater standards for copper were adopted in Cycle 5 (1994).

• Enforcement standard = 1,300 µg/L
• Preventive action limit = 130 µg/L

Copper is a naturally occurring metal that is used to make wires and pipes, treat plants, control algae, and preserve wood, leather, and fabrics. Small amounts of copper are needed for good health, but studies among people have shown that high levels of copper exposure can cause stomach problems (nausea, vomiting, diarrhea) and very high levels can damage the liver and kidneys.

Cyanazine

The groundwater standards for cyanazine were adopted in Cycle 2 (1988) and updated in Cycle 7 (1999).

• Enforcement standard = 1 µg/L
• Preventive action limit = 0.1 µg/L

Cyanazine is a herbicide used to control weeds in a variety of agricultural crops. Animal studies have shown that cyanazine can cause vomiting, affect body weight, damage the kidney and livers, change blood chemistry, and cause birth defects.

Cyanide

The groundwater standards for free cyanide were adopted in Cycle 1 (1985) and updated in Cycle 6 (1995).

• Enforcement standard = 200 µg/L
• Preventive action limit = 40 µg/L

Cyanide is used in the electroplating industry, in metal-cleaning operations, and as an industrial insect killer. Animal studies have shown that cyanide can cause birth defects. Studies among people have shown that high levels of cyanide exposure can cause sudden loss of consciousness or death, and exposure to low levels of cyanide over long periods of time can cause nerve damage and may impact the thyroid.

Dacthal

The groundwater standards for dacthal were adopted in Cycle 6 (1995) and updated in Cycle 8 (2006).

• Enforcement standard = 70 µg/L
• Preventive action limit = 14 µg/L

Dacthal (dimethyl tetrachloroterephthalate) is a pesticide product used for the control of annual grasses and certain broad-leaved weeds affecting various fruit and vegetable crops and ornamental turfs. Animal studies have shown that dacthal exposure for long periods of time can cause damage to the liver and kidneys.

Di (2-ethylhexyl) phthalate

The groundwater standards for di (2)-ethylhexyl) phthalate were adopted in Cycle 4 (1992) and updated in Cycle 6 (1995).

• Enforcement standard = 6 µg/L
• Preventive action limit = 0.6 µg/L

Di (2-ethylhexyl) phthalate is a man-made chemical that is commonly added to plastics to make them flexible. Animal studies have shown that di (2-ethylhexyl) phthalate can affect sperm and delay sexual maturity.

1,2-Dibromo-3-chloropropane (DBCP)

The groundwater standards for 1,2-dibromo-3-chloropropane were adopted in Cycle 3 (1990) and updated in Cycle 6 (1995).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

1,2-Dibromo-3-chloropropane is a man-made chemical used to make materials that resist burning. While the biggest health concerns come from breathing 1,2-dibromo-3-chloropropane, animal studies have shown that swallowing high levels can cause birth defects.

Dibromochloromethane

The groundwater standards for dibromochloromethane were adopted in Cycle 1 (1985) and updated in Cycle 5 (1994).

• Enforcement standard = 60 µg/L
• Preventive action limit = 6 µg/L

Dibromochloromethane is a naturally occurring liquid that can be formed when water is treated with chlorine to kill germs. Animal studies have shown that dibromochloromethane exposure can damage the liver and kidneys.

1,2-Dibromoethane (EDB)

The groundwater standards for 1,2-dibromoethane were adopted in Cycle 1 (1985) and updated in Cycle 5 (1994).

• Enforcement standard = 0.05 µg/L
• Preventive action limit = 0.005 µg/L

1,2-Dibromoethane (EDB) is a man-made chemical that is used as a pesticide on lumber and beehives, and to prepare dyes and waxes. It has also historically been used as a pesticide on soil and crops, and an additive in leaded gasoline. Studies among people have shown that long-term exposure to 1,2-dibromoethane can affect sperm and reduce fertility.

Dibutyl phthalate

The groundwater standards for dibutyl phthalate were adopted in Cycle 7 (1999) and updated in Cycle 9 (2010).

• Enforcement standard = 1,000 µg/L
• Preventive action limit = 100 µg/L

Dibutyl phthalate is a man-made chemical that is added to plastics to make them more flexible. Animal studies have shown that dibutyl phthalate exposure can affect the liver and blood.

Dicamba

The groundwater standards for dicamba were adopted in Cycle 3 (1990).

• Enforcement standard = 300 µg/L
• Preventive action limit = 60 µg/L

Dicamba is a pesticide used to control weeds on a variety of plants. Animal studies have shown that dicamba can affect body weight.

1,2-Dichlorobenzene

The groundwater standards for 1,2-dichlorobenzene were adopted in Cycle 2 (1988) and updated in Cycle 5 (1994).

• Enforcement standard = 600 µg/L
• Preventive action limit = 60 µg/L

1,2-Dichlorobenzene is a man-made chemical that is used to make herbicides. Animal studies have shown that 1,2-dichlorobenzene exposure can affect the liver, kidneys, blood, and body weight.

1,3-Dichlorobenzene

The groundwater standards for 1,3-dichlorobenzene were adopted in Cycle 2 (1988) and updated in Cycle 9 (2010).

• Enforcement standard = 600 µg/L
• Preventive action limit = 120 µg/L

1,3-Dichlorobenzene is a man-made chemical that is used to make herbicides, insecticides, medicine, and dyes. Animal studies have shown that 1,3-dichlorobenzene exposure can affect the liver, thyroid, and pituitary gland.

1,4-Dichlorobenzene

The groundwater standards for 1,4-dichlorobenzene were adopted in Cycle 1 (1985) and updated in Cycle 3 (1990).

• Enforcement standard = 75 µg/L
• Preventive action limit = 15 µg/L

1,4-Dichlorobenzene is a man-made chemical that is used to make mothballs, bathroom deodorants, and some resins. Animal studies have shown that 1,4-dichlorobenzene can affect the kidneys and blood, cause liver tumors, and may affect the development of the nervous system.

Dichlorodifluoromethane

The groundwater standards for dichlorodifluoromethane were adopted in Cycle 5 (1994).

• Enforcement standard = 1,000 µg/L
• Preventive action limit = 200 µg/L

Dichlorodifluoromethane (Freon 12) is a chlorofluorocarbon (CFC) that is a commonly used refrigerant gas and propellant for insect aerosol bombs. Animal studies have shown that dichlorodifluoromethane exposure can affect body weight.

1,1-Dichloroethane

The groundwater standards for 1,1-dichloroethane were adopted in Cycle 2 (1988) and reviewed as part of Cycle 10.

• Enforcement standard = 850 µg/L
• Preventive action limit = 85 µg/L

1,1-Dichloroethane is a man-made chemical that is used to make other chemicals and plastic wrap, adhesives, and synthetic fibers. Animal studies have shown that 1,1-dichloroethane can cause kidney and liver damage, affect weight gain in pregnant animals, delay bone development of offspring, and may cause cancer. Studies among people have shown that high levels of 1,1-dichloroethane cause irregular heartbeats and central nervous system depression.

1,2-Dichloroethane

The groundwater standards for 1,2-dichloroethane were adopted in Cycle 1 (1985) and updated in Cycle 3 (1990).

• Enforcement standard = 5 µg/L
• Preventive action limit = 0.5 µg/L

1,2-Dichloroethane is a man-made chemical that is used to make other chemicals, as a solvent for cleaning and degreasing, and to remove lead from gasoline. Animal studies have shown that 1,1-dichloroethane exposure can affect the immune and nervous systems, kidneys, and liver, and may cause stomach, lung, breast, and other types of cancer.

1,1-Dichloroethylene

The groundwater standards for 1,1-dichloroethylene were adopted in Cycle 2 (1988) and updated in Cycle 3 (1990).

• Enforcement standard = 7 µg/L
• Preventive action limit = 0.024 µg/L

1,1-Dichloroethylene (1,1-DCE) is a man-made chemical used to make fire-retardant materials and food packaging. Animal studies have shown that 1,1-DCE can affect the lungs, liver, and kidneys and may cause kidney and adrenal gland tumors.

1,2-Dichloroethylene (cis)

The groundwater standards for 1,2-dichloroethylene (cis) were adopted in Cycle 2 (1988) and updated in Cycle 5 (1994).

• Enforcement standard = 70 µg/L
• Preventive action limit =7 µg/L

1,2-Dichloroethylene (cis) is a man-made chemical that is used to produce solvents. While biggest health concerns come from breathing 1,2-dichloroethylene (cis), animal studies have shown that 1,2-dichloroethylene (cis) exposure can affect the blood and liver.

1,2-Dichloroethylene (trans)

The groundwater standards for 1,2-dichloroethylene (trans) were adopted in Cycle 2 (1988).

• Enforcement standard = 100 µg/L
• Preventive action limit =20 µg/L

1,2-Dichloroethylene (trans) is a man-made chemical that is used to produce solvents. While the biggest health concerns come from breathing 1,2-dichloroethylene (trans), animal studies have shown that 1,2-dichloroethene (trans) exposure can affect the lungs, liver, and heart.

2,4-dichlorophenoxyacetic acid

The groundwater standards for 2,4-dichlorophenoxyacetic acid were adopted in Cycle 1 (1985), enforcement standard was updated in Cycle 3 (1990), and the preventive action limit was updated in Cycle 5 (1994).

• Enforcement standard = 70 µg/L
• Preventive action limit =7 µg/L

2,4-dichlorophenoxyacetic acid (2,4-D) is a herbicide that is used to control weeds and invasive species in ponds and lakes. Animal studies have shown that 2,4-D can damage the kidneys and liver and may cause birth defects at high levels.

1,2-Dichloropropane

The groundwater standards for 1,2-Dichloropropane were adopted in Cycle 4 (1992).

• Enforcement standard = 5 µg/L
• Preventive action limit =0.5 µg/L

1,2-Dichloropropane (1,2-DCP) was previously used as an oil, fat solvent, degreaser, and dry cleaning solvent; however, it is currently only used in research and is not currently found in household products. Animal studies have shown that 1,2-DCP can affect the testes and decrease male fertility and can damage the liver, kidney, and brain.

1,3-Dichloropropene

The groundwater standards for 1,3-dichloropropene were adopted in Cycle 6 (1995) and were updated in 2010 (Cycle 9).

• Enforcement standard = 0.4 µg/L
• Preventive action limit =0.04 µg/L

1,3-Dichloropropene is a pesticide used to control nematodes (roundworms) in agricultural crops. Animal studies have shown that 1,2-dichloroproprene exposure can damage the stomach lining, cause skin and eye irritation, and cause anemia.

Dimethenamid

The groundwater standards for dimethenamid were adopted in Cycle 9 (2010).

• Enforcement standard = 50 µg/L
• Preventive action limit = 5 µg/L

Dimethenamid is a herbicide used to control a variety of weeds. Animal studies have shown that dimethenamid can impact the liver, body weight, and impact female reproduction.

Dimethoate

The groundwater standards for Dimethoate were adopted in Cycle 3 (1990).

• Enforcement standard = 2 µg/L
• Preventive action limit =0.4 µg/L

Dimethoate is a pesticide used to kill a wide range of insects. Animal studies have shown that dimethoate exposure can cause gastrointestinal and neurological effects.

2,4-Dinitrotoluene

The groundwater standards for 2,4-dinitrotoluene were adopted in Cycle 4 (1992).

• Enforcement standard = 0.05 µg/L
• Preventive action limit =0.005 µg/L

Dinitrotoluenes (DNTs) are man-made chemicals used to make other chemicals, dyes, and polyurethane foams. 2,4-Dinitrotoluene (2,4-DNT) is one form of DNT and it is usually found as a mixture with 2,6-DNT. Animal studies have shown that DNTs can damage the lungs, nervous system, male reproductive system, and liver and cause anemia (low blood count). Among studies in people, exposure to DNTs was shown to cause anemia, headaches, and dizziness.

2,6-Dinitrotoluene

The groundwater standards for 2,6-dinitrotoluene were adopted in Cycle 4 (1992).

• Enforcement standard = 0.05 µg/L
• Preventive action limit =0.005 µg/L

Dinitrotoluenes (DNTs) are man-made chemicals used to make other chemicals, dyes, and polyurethane foams. 2,6-Dinitrotoluene (2,6-DNT) is one form of DNT and it is usually found as a mixture with 2,4-DNT. Animal studies have shown that DNTs can damage the lungs, nervous system, male reproductive system, and liver, and cause anemia (low blood count). Among studies in people, 2,6-DNT exposure was shown to cause anemia, headaches, and dizziness.

Dinitrotoluene (total residues)**

The groundwater standards for dinitrotoluene (total residues) were adopted in Cycle 9 (2010).

• Enforcement standard = 0.05 µg/L
• Preventive action limit = 0.005 µg/L

Dinitrotoluenes (DNTs) are man-made chemicals used to make other chemicals, dyes, and polyurethane foams. They are found in six forms and are typically found in mixtures of 2,4-DNT and 2,6-DNT with smaller amounts of 2,3-DNT, 2,5-DNT, 3,4-DNT, and 3,5-DNT. Animal studies have shown that DNTs can damage the lungs, nervous system, male reproductive system, and liver and cause anemia (low blood count). Among studies in people, 2,4-DNT exposure was shown to cause anemia, headaches, and dizziness.

Dinoseb

The groundwater standards for dinoseb were adopted in Cycle 1 (1985) and were updated in 1995 (Cycle 6).

• Enforcement standard = 7 µg/L
• Preventive action limit = 1.4 µg/L

Dinoseb is a pesticide used to kill or control plants. Animal studies have shown that dinoseb can cause neurological effects, weight loss, and damage the thyroid, testes, and intestines.

1,4-Dioxane

The groundwater standards for 1,4-dioxane were adopted in Cycle 9 (2010) and reviewed as part of Cycle 10.

• Enforcement standard = 0.35 µg/L
• Preventive action limit = 0.035 µg/L

1,4-Dioxane is a man-made chemical used to make other chemicals. Animal studies have shown that 1,4-dioxane can result in liver and kidney damage and nasal irritation and inflammation.

Dioxin

The groundwater standards for dioxin were adopted in Cycle 3 (1990) and were updated in 1995 (Cycle 6).

• Enforcement standard = 0.00003 µg/L
• Preventive action limit = 0.000003 µg/L

Dioxin (2,3,7,8-tetrachlorodibenzodioxin) is formed during the chlorine bleaching process at pulp and paper mills and during chlorination by waste and drinking water treatment plants. Animal studies have shown that dioxin can cause weight loss, liver damage, disruption of the endocrine system, weaken the immune system, death, and severe birth defects when exposed during pregnancy.

Endrin

The groundwater standards for endrin were adopted in Cycle 1 (1985) and were updated in 1995 (Cycle 6).

• Enforcement standard = 2 µg/L
• Preventive action limit = 0.4 µg/L

Endrin is a pesticide used to control insects, rodents, and birds. Animal studies have shown that endrin can cause death, convulsions, and severe impacts to the central nervous system (brain and spinal cord).

EPTC

The groundwater standards for EPTC were adopted in Cycle 2 (1988).

• Enforcement standard = 250 µg/L
• Preventive action limit = 50 µg/L

EPTC (S-Ethyl dipropylthiocarbamate) is a herbicide used to control broadleaf weeds, grasses, and sedges in several food and non-food crops. Animal studies have shown that EPTC can cause brain cell death, developmental effects, cardiac damage, and nerve and muscle deterioration.

Ethyl ether

The groundwater standards for ethylene glycol were adopted in Cycle 9 (2010).

• Enforcement standard = 1000 µg/L
• Preventive action limit = 100 µg/L

Ethyl ether is a liquid that is used in the production of plastics and starting fuel for gasoline engines. Ethyl ether was a popular anesthetic in the late 1800s and early 1900s; however, it is no longer used today. Animal studies have shown that ethyl ether exposure can cause damage to the liver and blood and high levels of ethyl ether exposure can lead to respiratory arrest and death. Studies among people have shown ethyl ether exposure can cause irregular respiration, lung irritation, and loss of consciousness.

Ethylbenzene

The groundwater standards for ethyl ether were adopted in Cycle 2 (1988) and updated in Cycle 5 (1994).

• Enforcement standard = 700 µg/L
• Preventive action limit = 140 µg/L

Ethylbenzene is naturally found in coal tar and petroleum and is found in manufactured products such as inks, pesticides, and paints. Animal studies have shown that ethylbenzene can cause eye and throat irritation, dizziness, inner ear and hearing damage, and kidney damage.

Ethylene glycol

The groundwater standards for ethylene glycol were adopted in Cycle 5 (1994) and updated in Cycle 9 (2010).

• Enforcement standard = 14 mg/L
• Preventive action limit = 2.8 mg/L

Ethylene glycol is used to make antifreeze and de-icing solutions for cars, airplanes, and boats and is also used in hydraulic brake fluids. Animal studies have shown that high levels of ethylene glycol can affect kidney function, the nervous system, lungs, and heart.

Fluoranthene

The groundwater standards for fluoranthene were adopted in Cycle 7 (1999).

• Enforcement standard = 400 µg/L
• Preventive action limit = 80 µg/L

Fluoranthene is a polyaromatic hydrocarbon (PAH). It is released naturally during the burning of fossil fuels and wood. Animal studies have shown that fluoranthene exposure for long periods of time can cause kidney disease, increase liver weight, and increase liver enzyme levels.

Fluorene

The groundwater standards for fluorene were adopted in Cycle 6 (1995).

• Enforcement standard = 400 µg/L
• Preventive action limit = 80 µg/L

Fluorene is a polyaromatic hydrocarbon (PAH). It is used in resins, dyes, and other chemicals and is released naturally during the burning of fossil fuels and wood. Animal studies have shown that fluorene can irritate and burn eyes and skin and long-term exposure to fluorene can affect respiration, blood, and liver enzymes.

Fluoride

The groundwater standards for fluoride were adopted in Cycle 1 (1985) and was updated in cycle 2 (1988) and again in Cycle 3 (1990).

• Enforcement standard = 4 mg/L
• Preventive action limit = 0.8 mg/L

Fluoride is a naturally occurring mineral that is sometimes added to drinking water supplies to prevent dental cavities. It can also be found in a variety of dental compounds including toothpaste and mouth rinses. Animal studies have shown that very high levels of fluoride exposure can cause bones to be brittle and fragile.

Fluorotrichloromethane

The groundwater standards for fluorotrichloromethane were adopted in Cycle 2 (1988).

• Enforcement standard = 3490 µg/L
• Preventive action limit = 698 µg/L

Fluorotrichloromethane is a type of Freon gas. Before the 1970s, it was used as coolants or pressurizers in spray can products. The biggest health concerns come from breathing fluorotrichloromethane. Studies among people have shown that exposure to fluorotrichloromethane in air can cause irritation of the mouth, throat, lungs, and nose; heart palpitations; and dizziness.

Formaldehyde

The groundwater standards for formaldehyde were adopted in Cycle 5 (1994).

• Enforcement standard = 1000 µg/L
• Preventive action limit = 100 µg/L

Formaldehyde is used to make fabrics in permanent-press clothing and draperies and was used in foam insulation in the 1970s. The biggest health concerns come from breathing formaldehyde. Studies among people have shown that exposure to formaldehyde in the air can irritate the eyes, throat, and nose with higher levels being associated with nausea, chest tightness, and wheezing.

Heptachlor

The groundwater standards for heptachlor were adopted in Cycle 5 (1994).

• Enforcement standard = 0.4 µg/L
• Preventive action limit = 0.04 µg/L

Heptachlor is a pesticide used for fire ant control in power transformers but was previously used for killing insects in homes, buildings, and on food crops. Animal studies have shown that heptachlor can cause liver damage, excitability, and decreased fertility.

Heptachlor epoxide

The groundwater standards for heptachlor epoxide were adopted in Cycle 5 (1994).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Heptachlor epoxide is a breakdown product of the pesticide, heptachlor. Since heptachlor and heptachlor epoxide are similar, it is likely that heptachlor epoxide causes health effects similar to those caused by heptachlor, such as liver damage, excitability, and decreased fertility.

Hexachlorobenzene

The groundwater standards for hexachlorobenzene were adopted in Cycle 6 (1995).

• Enforcement standard = 1 µg/L
• Preventive action limit = 0.1 µg/L

Hexachlorobenzene is a waste product formed during the manufacture of other chemicals and can be found as an impurity in some pesticides. Hexachlorobenzene has been shown to affect the nervous system through weakness, tremors, and convulsions; cause skin sores; and damage the liver, kidney, and thyroid.

n-Hexane

The groundwater standards for n-hexane were adopted in Cycle 7 (1999).

• Enforcement standard = 600 µg/L
• Preventive action limit = 120 µg/L

n-Hexane is a chemical made from crude oil that is used as a solvent for extracting vegetable oils from crops; component of gasoline; and in the production of tires, glues, tape, and bandages. The biggest health concerns come from breathing n-hexane. Studies among people have shown that breathing in large amounts of n-hexane can cause numbness in lower legs and feet.

Hydrogen Sulfide

The groundwater standards for hydrogen sulfide were adopted in Cycle 7 (1999).

• Enforcement standard = 30 µg/L
• Preventive action limit = 6 µg/L

Hydrogen sulfide is a gas that is formed naturally and is a common byproduct of industrial processes like petroleum refining, natural gas production, and food processing. The biggest health concerns come from breathing hydrogen sulfide. Breathing in large amounts of hydrogen sulfide can cause irritation to the eyes, nose, or throat; headaches; poor memory; tiredness; and balance problems.

Lead

The groundwater standards for lead were adopted in Cycle 1 (1985) and were updated in Cycle 5 (1994).

• Enforcement standard = 15 µg/L
• Preventive action limit = 1.5 µg/L

Lead is a heavy metal found in old paint, leaded gasoline, plumbing materials, and certain household items. There is no safe level of lead. Lead has been shown to effect neurological and cognitive development; health; behavior, like aggression and violence; and learning and school performance.

Lindane

The groundwater standards for lindane were adopted in Cycle 1 (1985) and were updated in Cycle 5 (1994).

• Enforcement standard = 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Lindane, also known as gamma-hexachlorocyclohexane, is a pesticide used on fruit, vegetables, and forest crops, and is an ingredient in shampoos that treat for head and body lice. Animal studies have shown that lindane can cause convulsions, liver and kidney effects, reduced ability to fight infection, and injury to the ovaries and testes.

Manganese

The groundwater standards for manganese were adopted in Cycle 9 (2010).

• Enforcement standard = 300 µg/L
• Preventive action limit = 60 µg/L

Manganese is a common element found in minerals, rocks, and soil but is also a product of human activities like steel production and mining. Animal studies have shown that manganese exposure can affect reproduction and damage the kidneys. Studies among people have shown that high levels of manganese can affect the nervous system and suggest that people over the age of 50 and infants less 6 months are the most sensitive to these effects.

Mercury

The groundwater standards for mercury were adopted in Cycle 1 (1985).

• Enforcement standard = 2 µg/L
• Preventive action limit = 0.2 µg/L

Mercury is a naturally occurring metal that is used in a number of industrial and household products. The nervous system is very sensitive to all forms of mercury. Studies among people have shown that high levels of mercury exposure can permanently damage the brain, kidneys, and developing babies.

Methanol

The groundwater standards for methanol were adopted in Cycle 7 (1999).

• Enforcement standard = 5000 µg/L
• Preventive action limit = 1000 µg/L

Methanol (also known as wood alcohol) is a naturally occurring liquid that is used in the production of formaldehyde, plastics and other chemicals and is used in antifreeze, fuels, and pharmaceuticals. Animal studies have shown that exposure to lower levels of methanol during pregnancy can cause birth defects. Studies among people have shown that drinking high levels of methanol can result in headaches, blurred vision, muscle pain, blindness, and death.

Methoxychlor

The groundwater standards for methoxychlor were adopted in Cycle 1 (1985) and updated in 1994 (Cycle 5).

• Enforcement standard = 40 µg/L
• Preventive action limit = 4 µg/L

Methoxychlor is a man-made pesticide used on flies, mosquitoes, cockroaches, and other insects. Animals studies have shown that high levels of methoxychlor can cause tremors, convulsions, and seizures.

Methyl ethyl ketone

The groundwater standards for methyl ethyl ketone were adopted in Cycle 4 (1992) and updated in Cycle 9 (2010).

• Enforcement standard = 4 mg/L
• Preventive action limit = 0.8 mg/L

Methyl ethyl ketone (also known as 2-butanone) is a man-made chemical used in paints and other coatings and in glues and cleaning agents. Animal studies have shown that methyl ethyl ketone exposure can cause nervous system effects including drooping eyelids and uncoordinated muscle movements.

Methyl isobutyl ketone

The groundwater standards for methyl isobutyl ketone were adopted in Cycle 5 (1994).

• Enforcement standard = 500 µg/L
• Preventive action limit = 50 µg/L

Methyl isobutyl ketone (MIBK), also called isopropylacetone, is a naturally occurring chemical that is used in home products like hard surface cleaners, dyes and tints, laundry starches, paints, and varnish products. While the biggest health concerns come from breathing methyl isobutyl ketone, animal studies have shown that methyl isobutyl ketone can cause liver and kidney damage.

Methyl tert-butyl ether

The groundwater standards for methyl tert-butyl ether were adopted in Cycle 4 (1992).

• Enforcement standard= 60 µg/L
• Preventive action limit = 12 µg/L

Methyl tert-butyl ether (MTBE) is a chemical added to gasoline so that engines produce less carbon monoxide and other carbon-containing air pollutants. Animal studies have shown that exposure to high levels of methyl tert-butyl ether over long periods of time may increase the risk of certain types of cancer.

Methylene chloride

The groundwater standards for methylene chloride were adopted in Cycle 1 (1985) and updated in Cycle 6 (1995).

• Enforcement standard= 5 µg/L
• Preventive action limit = 0.5 µg/L

Methylene chloride (also known as dichloromethane) is a man-made liquid that is used as paint remover, industrial solvent, and grain disinfectant. It can also be formed when drinking water is disinfected with chlorine. While biggest health concerns come from breathing methylene chloride, animal studies have shown that swallowing high levels of methylene chloride over long periods of time can damage the liver and cause liver tumors.

Metolachlor

The groundwater standards for metolachlor were adopted in Cycle 2 (1988) and updated in Cycle 9 (2010).

• Enforcement standard= 100 µg/L
• Preventive action limit = 10 µg/L

Metolachlor is a pesticide used to treat weeds in a number of agricultural, lawn, and forest plants. Animal studies have shown that metolachlor can affect the liver, body weight, and offspring development.

Metolachlor ESA and OXA

The combined groundwater standards for metolachlor ethane sulfonic acid (ESA) and metolachlor oxanilic acid (OSA) were adopted in Cycle 9 (2010).

• Enforcement standard= 1.3 mg/L
• Preventive action limit = 0.26 mg/L

Metolachlor ESA and metolachlor OXA are breakdown products of the pesticide, metolachlor. Animal studies have shown that metolachlor ESA and OXA have very little toxicity.

Metribuzin

The groundwater standards for metribuzin were adopted in Cycle 3 (1990) and updated in Cycle 9 (2010).

• Enforcement standard= 70 µg/L
• Preventive action limit = 14 µg/L

Metribuzin is a pesticide used to control weeds in corn, soybeans, potatoes, and other crops. Animal studies have shown that metribuzin exposure can affect the thyroid, liver, blood, development, and body weight.

Molybdenum

The groundwater standards for molybdenum were adopted in Cycle 8 (2006) and reviewed as part of Cycle 10.

• Enforcement standard= 40 µg/L
• Preventive action limit = 8 µg/L

Molybdenum is a natural mineral that is used in the production of cast iron and stainless steel, biofuels, solar panels, catalysts, lubricants, and pigments. Animal studies have shown that molybdenum exposure may cause kidney and liver damage and high levels of molybdenum exposure can cause reproductive and developmental effects (decreases in growth).

Monochlorobenzene

The groundwater standards for monochlorobenzene were adopted in Cycle 4 (1992).

• Enforcement standard= 100 µg/L
• Preventive action limit = 20 µg/L

Monochlorobenzene (also known as chlorobenzene) is a man-made chemical used to degrease automobile parts and to make other chemicals and pesticides. Animal studies have shown that monochlorobenzene exposure can damage the liver, kidney, and central nervous system.

Naphthalene

The groundwater standards for naphthalene were adopted in Cycle 4 (1992) and updated in Cycle 8 (2006).

• Enforcement standard= 100 µg/L
• Preventive action limit = 10 µg/L

Naphthalene is found naturally in crude oil and is used to make dyes, explosives, plastics, and lubricants. Animals studies have shown that naphthalene exposure can cause anemia and liver and kidney damage. Studies among people have shown that high levels of naphthalene exposure can cause headaches, nausea, anemia, and damage to the liver, kidneys and the eyes.

Nickel

The groundwater standards for nickel were adopted in Cycle 6 (1995).

• Enforcement standard= 100 µg/L
• Preventive action limit = 20 µg/L

Nickel is a naturally occurring metal that is used with other metals to make coins, jewelry, valves, heat exchangers, and to make stainless steel. Animal studies have shown that high levels of nickel impacted the lungs, stomach, blood, liver, kidneys, immune system, reproduction, and development. Studies among people have shown that high levels of nickel exposure from water consumption experienced stomachaches and blood and kidney effects.

Nitrate

The groundwater standards for nitrate were adopted in Cycle 5 (1994).

• Enforcement standard= 10 mg/L (as nitrate-nitrogen)
• Preventive action limit = 2 mg/L (as nitrate-nitrogen)

Nitrate is a naturally occurring molecule that can enter groundwater from fertilizers and animal and human waste. Exposure to high levels of nitrate may cause methemoglobinemia (also known as blue baby syndrome), certain types of birth defects, and increase the risk of thyroid disease and colon cancer.

Nitrite

The groundwater standards for nitrite were adopted in Cycle 5 (1994).

• Enforcement standard= 1 mg/L (as nitrite-nitrogen)
• Preventive action limit = 0.2 mg/L (as nitrite-nitrogen)

Nitrite is a naturally occurring molecule that is can enter groundwater from fertilizers and animal and human waste. It is also used in food preservation, some medications, and the production of munitions and explosives. High levels of nitrite can cause methemoglobinemia (also known as blue baby syndrome).

Nitrite + Nitrate

The groundwater standards for nitrite and nitrate combined were adopted in Cycle 1 (1985).

• Enforcement standard= 10 mg/L (as nitrogen)
• Preventive action limit = 2 mg/L (as nitrogen)

Nitrate and nitrite are naturally occurring molecules that can enter groundwater from fertilizers and animal and human waste. Exposure to high levels of nitrate and nitrite may cause methemoglobinemia (also known as blue baby syndrome), certain types of birth defects, and increase the risk of thyroid disease and colon cancer.

N-Nitrosodiphenylamine

The groundwater standards for n-nitrosodiphenylamine were adopted in Cycle 7 (1999).

• Enforcement standard= 7 µg/L
• Preventive action limit = 0.7 µg/L

N-Nitrosodiphenylamine is a chemical that was used by several companies in the United States to make rubber until the early 1980s. Currently there is only one company using it. Animal studies have shown that high levels of n-nitrosodiphenylamine can cause swelling, cancer of the bladder, changes in body weight, and death.

Pentachlorophenol

The groundwater standards for pentachlorophenol were adopted in Cycle 3 (1990) and updated in Cycle 5 (1994).

• Enforcement standard= 1 µg/L
• Preventive action limit = 0.1 µg/L

Pentachlorophenol is a man-made chemical that is used as a pesticide and wood preservative. Animal studies have shown that pentachlorophenol can cause liver and immune system damage. Studies among people have shown that high levels of pentachlorophenol can cause cells in the body to produce excess heat leading to high fever, sweating, difficulty breathing, organ and tissue injury, and potentially death.

Perchlorate

The groundwater standards for perchlorate were adopted in Cycle 9 (2010).

• Enforcement standard= 1 µg/L
• Preventive action limit = 0.1 µg/L

Perchlorates are a class of chemicals that are used in explosives, fireworks, rocket motors, and used for making other chemicals. Animal studies have shown that perchlorates can result in thyroid damage and affect hormone levels. Studies among people have shown that high levels of perchlorate for long periods of time can affect the thyroid gland and cause anemia.

Phenol

The groundwater standards for phenol were adopted in Cycle 4 (1992) and updated in Cycle 9 (2010).

• Enforcement standard= 2 mg/L
• Preventive action limit = 0.4 mg/L

Phenol is a chemical that is used to make resins, nylon, other man-made fibers; as a disinfectant and antiseptic; and to kill bacteria in slime. Animal studies have shown that high levels of phenol can cause muscle tremors and loss of coordination.

Picloram

The groundwater standards for picloram were adopted in Cycle 6 (1995).

• Enforcement standard= 500 µg/L
• Preventive action limit = 100 µg/L

Picloram is a man-made pesticide used for killing weeds along roadways, ditches, and on non-productive land, forest land, and commercial or industrial properties. Animal studies have shown that picloram exposure can cause weakness, diarrhea, weight loss, liver damage, and damage to the central nervous system.

Polychlorinated biphenyls

The groundwater standards for polychlorinated biphenyls were adopted in Cycle 4 (1992).

• Enforcement standard= 0.03 µg/L
• Preventive action limit = 0.003 µg/ L

Polychlorinated biphenyls (PCBs) were manufactured for use as coolants in electrical equipment, in metal-cutting oils, in microscope lens oils, and in inks, dyes, and carbonless copy paper. In 1977, the U.S. Environmental Protection Agency (EPA) banned PCB use. PCBs can accumulate in the environment. Animal studies have shown that PCBs may cause liver cancer, liver damage, and may affect the immune system, reproduction, and the development of unborn babies.

Prometon

The groundwater standards for prometon were adopted in Cycle 7 (1999) and revised in Cycle 9 (2010).

• Enforcement standard= 100 µg/L
• Preventive action limit = 20 µg/L

Prometon is a man-made pesticide used for weed control on industrial sites. Animal studies have shown that consuming high levels of prometon can result in adverse effects on growth.

Propazine

The groundwater standards for propazine were adopted in Cycle 9 (2010).

• Enforcement standard= 10 µg/L
• Preventive action limit = 2 µg/L

Propazine is a man-made pesticide used to control broadleaf weeds that can be applied before planting, at planting, and after crop emergence. Animal studies have shown that propazine may cause weight loss and affect the endocrine system, which is a system of glands that produce hormones.

Pyrene

The groundwater standards for pyrene were adopted in Cycle 7 (1999).

• Enforcement standard= 250 µg/L
• Preventive action limit = 50 µg/L

Pyrene is used to make dyes, plastics, and pesticides. Animal studies have shown that pyrene may affect the liver, kidneys, and blood.

Pyridine

The groundwater standards for pyridine were adopted in Cycle 7 (1999).

• Enforcement standard= 10 µg/L
• Preventive action limit = 2 µg/L

Pyridine is used to dissolve other substances and to make a variety of products including medicines, vitamins, food flavorings, paints, dyes, rubber products, adhesives, and pesticides. Animal studies have shown that pyridine exposure can cause liver and kidney damage and skin and eye irritation.

Selenium

The groundwater standards for selenium were adopted in Cycle 1 (1985) and revised in Cycle 5 (1994).

• Enforcement standard= 50 µg/L
• Preventive action limit = 10 µg/L

Selenium is a naturally occurring element that is used in the electronics industry, glass, paints, enamels, inks rubber, and as a nutritional supplement. Selenium has both beneficial and harmful effects. Animal studies have shown that high levels of selenium exposure can cause nausea, vomiting, and diarrhea and long term exposure can lead to selenosis with symptoms of hair loss, nail brittleness, and neurological abnormalities.

Silver

The groundwater standards for silver were adopted in Cycle 1 (1985).

• Enforcement standard= 50 µg/L
• Preventive action limit = 10 µg/L

Silver is a naturally occurring element that can be combined with other elements for producing a wide range of products, including jewelry, silverware, electronic equipment, and dental fillings. Exposure to high levels of silver for a long period of time may result in a condition called argyria, a blue-gray discoloration of the skin and other body tissues.

Simazine

The groundwater standards for simazine were adopted in Cycle 1 (1985) and updated in Cycles 2 (1988), 4 (1992), and 6 (1995).

• Enforcement standard= 4 µg/L
• Preventive action limit = 0.4 µg/L

Simazine is an pesticide used to control broadleaf and grass weeds. Animal studies have shown that long-term exposure to high levels of simazine can affect body weight, thyroid function, impact the blood, and cause tumors.

Styrene

The groundwater standards for styrene were adopted in Cycle 5 (1994).

• Enforcement standard= 100 µg/L
• Preventive action limit = 10 µg/L

Styrene is widely used to make plastics and rubber. Products containing styrene include insulation, fiberglass, plastic pipes, automobile parts, shoes, drinking cups, and other food containers. Animal studies have shown that high levels of styrene can cause hearing loss, changes to the lining of the nose, and liver damage.

Tertiary butyl alcohol

The groundwater standards for tertiary butyl alcohol were adopted in Cycle 1 (1985).

• Enforcement standard= 12 µg/L
• Preventive action limit = 1.2 µg/L

Tertiary butyl alcohol is a man-made chemical that is added to gasoline to make it burn more efficiently. Animal studies have shown that long-term exposure to high levels of tertiary butyl alcohol damages the kidneys and thyroid and delayed development.

1,1,1,2-Tetrachloroethane

The groundwater standards for 1,1,1,2-tetrachloroethane were adopted in Cycle 1 (1985).

• Enforcement standard= 70 µg/L
• Preventive action limit = 7 µg/L

1,1,1,2-Tetrachloroethane (1,1,1,2-TCA) is used as a solvent and in the production of wood stains and varnishes. Animal studies have shown that high levels over long periods of time can affect the kidneys, liver, and nervous system.

1,1,2,2-Tetrachloroethane

The groundwater standards for 1,1,2,2-tetrachloroethane were adopted in Cycle 6 (1995).

• Enforcement standard= 0.2 µg/L
• Preventive action limit = 0.02 µg/L

1,1,2,2-Tetrachloroethane (1,1,2,2-TCA) is a manufactured chemical used as an industrial solvent to clean and degrease metals, and as an ingredient in paints and pesticides. Animal studies have shown that exposure to high levels of 1,1,2,2-TCA can cause liver damage, stomachaches, and dizziness.

Tetrachloroethylene

The groundwater standards for tetrachloroethylene were adopted in Cycle 1 (1985), updated in Cycle 5 (1994), and reviewed as part of Cycle 10.

• Enforcement standard= 5 µg/L
• Preventive action limit = 0.5 µg/L

Tetrachloroethylene (PCE) is a liquid solvent used in many applications, including dry cleaning and metal degreasing. Animal studies have shown that PCE exposure can cause liver, kidney, and central nervous system damage. Studies among people have shown that PCE exposure can cause mental confusion, loss of consciousness, liver and kidney damage, and affect unborn babies.

Tetrahydrofuran

The groundwater standards for tetrahydrofuran were adopted in Cycle 2 (1988).

• Enforcement standard= 50 µg/L
• Preventive action limit = 10 µg/L

Tetrahydrofuran is a solvent used for making rubber, resins, plastics, dyes, lacquers, spandex, adhesives, and food storage and packaging materials. Animal studies have shown that long-term exposure to high levels of tetrahydrofuran can damage the kidneys and affect development.

Thallium

The groundwater standards for thallium were adopted in Cycle 6 (1995).

• Enforcement standard= 2 µg/L
• Preventive action limit = 0.4 µg/L

Thallium is used to manufacture electronic devices, switches, and closures primarily for the semiconductor industry. Animal studies have shown that high levels of thallium exposure can affect reproduction and development. Studies among people who ingested large amounts of thallium over a short time have reported vomiting, diarrhea, temporary hair loss, and damage on the nervous system, lungs, heart, liver, and kidneys.

Toluene

The groundwater standards for toluene adopted in Cycle 1 (1985) and updated in Cycle 9 (2010).

• Enforcement standard= 800 µg/L
• Preventive action limit = 160 µg/L

Toluene occurs naturally in crude oil and is used in oil refining and the manufacturing of paints, lacquers, explosives, and glues. While the biggest health concerns come from toluene, animal studies have shown that high levels of toluene exposure over long periods of time can affect the liver, kidneys, and nervous system.

Toxaphene

The groundwater standards for toxaphene were adopted in Cycle 1 (1985) and updated in Cycle 5 (1994).

• Enforcement standard= 3 µg/L
• Preventive action limit = 0.3 µg/L

Toxaphene is a mixture of hundreds of different chlorinated compounds primarily used to control insect pests on cotton and other crops. The EPA banned all uses of toxaphene in 1990. Animal studies have shown that long-term exposure to high levels of toxaphene can damage the liver, kidneys, alter the immune system, and cause cancer.

1,2,4-Trichlorobenzene

The groundwater standards for 1,2,4-trichlorobenzene were adopted in Cycle 6 (1995).

• Enforcement standard= 70 µg/L
• Preventive action limit = 14 µg/L

1,2,4-Trichlorobenzene is a man-made chemical used to dissolve materials such as oils, waxes, resins, greases, and rubber. Animal studies have shown that high levels of 1,2,4-trichhlorobenzene exposure for prolonged periods of time can cause liver and kidney damage.

1,1,1-Trichloroethane

The groundwater standards for 1,1,1-Trichloroethane were adopted in Cycle 1 (1985).

• Enforcement standard= 200 µg/L
• Preventive action limit = 40 µg/L

1,1,1-Trichloroethane (1,1,1-TCA) is a man-made chemical used for metal degreasing, dry-cleaning solvent, and to make other chemicals. Animal studies have shown that long-term exposure to high levels of 1,1,1,-TCA can cause liver, lung, and brain damage.

1,1,2-Trichloroethane

The groundwater standards for 1,1,2-trichloroethane were adopted in Cycle 1 (1985) and updated in Cycle 6 (1995).

• Enforcement standard= 5 µg/L
• Preventive action limit = 0.5 µg/L

1,1,2-Trichloroethane is used as a solvent and is sometimes present as an impurity in other chemicals. It can be formed when another chemical breaks down in the environment. Animal studies have shown that long-term exposure to high levels of 1,1,2-Trichloroethane can affect the stomach, blood, liver, kidneys, and nervous system.

Trichloroethylene

The groundwater standards for trichloroethylene were adopted in Cycle 1 (1985), updated in Cycle 3 (1990), and reviewed as part of Cycle 10.

• Enforcement standard= 5 µg/L
• Preventive action limit = 0.5 µg/L

Trichloroethylene (TCE) is a man-made chemical that is used as a metal degreaser and can be found in paint, spot removers, carpet-cleaning fluids, metal cleaners, and varnishes. Animal studies have shown that exposure to large amounts of TCE over long periods of time can affect the kidneys, liver, lung, and immune system. TCE may cause certain heart defects in unborn babies.

2,4,5-Trichlorophenoxyporpionic acid

The groundwater standards for 2,4,5-trichlorophenoxyporpionic acid were adopted in Cycle 1 (1985) and updated in Cycle 5 (1994).

• Enforcement standard= 50 µg/L
• Preventive action limit = 5 µg/L

2,4,5-Trichlorophenoxyporpionic acid (2,4,5-TP or Silvex) is a pesticide that used to be used on farms, lawns, pastures, ditches, riverbanks and in lakes and ponds. Most uses of 2,4,5-TP were prohibited in 1984 due to concerns about contamination with dioxin. Animal studies have shown that large amounts of 2,4,5-TP can affect the liver and cause birth defects.

1,2,3-Trichloropropane

The groundwater standards for 1,2,3-trichloropropane were adopted in Cycle 7 (1999) and reviewed as part of Cycle 10.

• Enforcement standard= 60 µg/L
• Preventive action limit = 12 µg/L

1,2,3-Trichloropropane is a man-made chemical used to make other chemicals, industrial solvents, paint and varnish remover, and in cleaning and degreasing agents. Animal studies have shown that exposure to high levels of 1,2,3-trichloropropane over long periods of time can cause liver and kidney damage, blood disorders, and stomach irritation.

Trifluralin

The groundwater standards for trifluralin were adopted in Cycle 3 (1990).

• Enforcement standard= 7.5 µg/L
• Preventive action limit = 0.75 µg/L

Trifluralin is a pesticide used to control weeds in foods and other crops. Animal studies have shown that exposure to high levels of trifluralin over long periods of time can cause liver and kidney damage and may increase the risk of cancer.

Trimethylbenzenes

The combined groundwater standards for 1,2,4- and 1,3,5-trimethylbenzenes were adopted in Cycle 7 (1999).

• Enforcement standard= 480 µg/L
• Preventive action limit = 96 µg/L

A mixture of 1,2,4- and 1,3,5-trimethylbenzenes is commonly used as an industrial solvent in the manufacture of dyes, perfumes and resins and can also be found in some gasolines and paint solvents. While biggest health concerns come from breathing trimethylbenzenes, animal studies have shown that swallowing large amounts of trimethylbenzenes over long periods of time can affect the liver, blood, and overall health.

Vanadium

The groundwater standards for vanadium were adopted in Cycle 7 (1999.

• Enforcement standard= 30 µg/L
• Preventive action limit = 6 µg/L

Vanadium is a naturally occurring metal that is used in producing steels, ceramics, and superconductive magnets. Animal studies have shown that exposure to high levels of vanadium over long periods of time may affect red blood cells, increased blood pressure, and cause mild neurological effects.

Vinyl chloride

The groundwater standards for vinyl chloride were adopted in Cycle 1 (1985) and updated in Cycle 3 (1990).

• Enforcement standard= 0.2 µg/L
• Preventive action limit = 0.02 µg/L

Vinyl chloride is used to make polyvinyl chloride (PVC) pipes, wire coatings, vehicle upholstery, and plastic kitchenware. Animal studies have shown that long-term exposure to high levels of vinyl chloride may affect the nervous and immune systems, decrease in bone strength in fingers, arms, and joints, and increase the risk of liver, lung, and several other types of cancer.