Aquifer An underground water supply. A geologic formation that is water bearing and may store or transmit water to wells and springs. Aquifers may be used as a source of water for drinking or for other purposes.

Carcinogen– A cancer-causing substance.

Contaminant– Anything found in environmental media such as soil, water, or air (including microorganisms, minerals, chemicals, radionuclides, etc.) that may be harmful to human health.

Detection Limit– The lowest concentration of a contaminant that can be detected by laboratory analyses.

GenotoxicA substance that is damaging to DNA, therefore capable of causing mutations or cancer.

Groundwater– Groundwater is found under the earth’s surface “between rocks and soils” and in aquifers. Groundwater is typically composed of rain and snowmelt that seep through the soil and collect in the hollow spaces between soil and rocks.

Inorganic contaminant– According to the US EPA, inorganic contaminants are mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. The EPA has set legal limits on 15 inorganic contaminants in private drinking water.

Maximum Contaminant Level (MCL)– The MCL is a legally enforceable standard for the highest level of a contaminant that is allowed in drinking water. The MCL is established to protect human health from contaminants in drinking water while also considering the best available treatment technology and costs. The MCL is an enforceable standard for drinking water.

Maximum Contaminant Level Goal (MCLG)– The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.

Method Detection Limit (MDL)– The minimum concentration of a substance that can be measured and reported with 99-percent confidence that its concentration is greater than zero. In the TrAC project, values that were reported as below the method detection limits of the State Laboratory were assigned half of the detection limit for all county-level calculations. Half of the detection limit is assigned because it is known that all “below detects” fall somewhere between the detection limit and 0; this calculation assumes that they will follow a normal distribution and will be clustered around the median value in this range.

Mg/L– Milligrams per liter. Equivalent to parts per million (PPM). 1 mg/L is 1,000 times larger than 1 µg/L.

Non-point source pollution– Unlike point source pollution, non-point source pollution comes from different sources and usually accumulates as runoff occurs and pollutants are picked up by rain or snowmelt that flows across the land and into waterways.

Organic contaminant– Organic contaminants are carbon-based compounds such as solvents and pesticides, which can get into water through runoff from cropland, leaking from underground storage tanks and vehicles, or discharge from factories. The EPA has set legal limits on 56 organic contaminants.

Parts per billion (PPB)– Equivalent to µg/L (micrograms per Liter).

Parts per million (PPM)– Equivalent to mg/L (milligrams per Liter).

Point source pollution– Point source reflects any distinct and separate source of pollution. According to the US EPA, point source pollution may enter the environment from any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged. Point source pollution does not include agricultural storm water discharges and return flows from irrigated agriculture.

Primary contaminant– Primary Drinking Water Regulations are legally enforceable standards for public drinking water systems. Primary standards are designed to protect public health by limiting the levels of contaminants in drinking water. Primary contaminants are contaminants that in excess of the Maximum Contaminant Level (MCL) may pose a risk to human health.

Private well– Private wells are sources of water that are not provided by public drinking water systems and are therefore not regulated by the government. Private wells are typically drilled, dug, or bored into an underground aquifer and the water in the underground aquifer is pumped into the home. Many homes have a filter to reduce the likelihood that any contamination in groundwater will be released to household taps. Since 2008, all newly constructed wells in North Carolina must be tested for bacterial and chemical contaminants within 30 days of well completion. Some households with older wells or with wells that are not tested periodically may not know whether there are contaminants in their well water. According to the EPA, about 15 percent of Americans have their own sources of drinking water, such as wells, cisterns, and springs. Over 3 million people in North Carolina use domestic wells as their primary drinking water source.

Remediation– Actions taken by federal, state, or local agencies to remove contamination from a site and ensure that the site is no longer a threat to human or environmental health. Once all cleanup goals have been achieved, the site may be returned to safe and productive use or redeveloped. For more information about remediation, view the EPA explanation of the Superfund cleanup process.

Secondary contaminant– Secondary contaminants may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water.

Secondary Maximum Contaminant Level (SMCL)– Non-enforceable standards for secondary contaminants in drinking water. SMCLs may be based upon a contaminants likelihood to cause changes to the aesthetic (taste and odors), cosmetic (do not damage the body but are undesirable), or technical (may damage water fixtures or increase the availability of other contaminants) qualities of water.

Surface water– Water that is on the Earth’s surface and open to the atmosphere, such as in a stream, river, lake, or reservoir.

Trace– Presence of a contaminant that is not quantitatively detectable or large enough to be determined by current analytical laboratory methods. This is typically reported on the results form for organic contaminants that are below the detection limit.

µg/L– Micrograms per liter. Equivalent to parts per billion (PPB). 1 µg/L is 1,000 times smaller than 1 mg/L.


Director: Rebecca Fry, PhD
Deputy Director: Fernando Pardo-Manuel de Villena, PhD
Funding provided by NIEHS grant #P42 ES031007

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253 Rosenau Hall, CB #7431
Chapel Hill, NC, 27599-7431