Glossary
Water-quality terminology you'll see on lab reports, product spec sheets, and our blog — defined plainly.
No terms match
A
Air Quality Monitor A regulatory or research instrument, usually fixed at a known location, that continuously measures concentrations of specific air pollutants to determine compliance with standards like NAAQS. American Community Survey An ongoing U.S. Census Bureau survey collecting detailed annual data on income, race, education, language, and housing across the country. Asthma Rate The percentage of a population diagnosed with asthma. Frequently used as a public-health indicator of air-pollution exposure, since particulate matter and ozone trigger attacks.
C
Cancer Cluster A greater-than-expected number of cancer cases occurring within a specific group of people in a defined geographic area over a certain period. The CDC's official designation requires intense, long-term statistical analysis. Cancer Cluster Designation The official, statistically validated finding by a public health authority (such as the CDC or a state health department) that an area's cancer rates exceed expectations and warrant deeper investigation. Carbon Monoxide A colorless, odorless toxic gas formed by incomplete combustion of fuels. At elevated levels it reduces the blood's ability to deliver oxygen to body tissues. CDC PLACES A CDC dataset providing local-level estimates of chronic disease, health risk behaviors, and prevention measures down to the census-tract level. Census Tract A small statistical subdivision of a county (typically 1,200 to 8,000 people) used by the Census Bureau as a stable geographic unit for reporting demographic and health data. Centers for Disease Control and Prevention The U.S. federal public health agency that tracks disease and is the body that officially evaluates and designates cancer clusters. Chemical Spill An unplanned release of a hazardous chemical into the environment, often the result of an industrial accident, transportation incident, or equipment failure. Criteria Pollutants The six common air pollutants regulated under NAAQS: ground-level ozone, particulate matter, carbon monoxide, lead, sulfur dioxide, and nitrogen dioxide. Cumulative Burden Threshold A scoring cutoff (for example, the top 5% nationally for both poverty and pollution exposure) above which a neighborhood becomes officially designated as a disadvantaged or overburdened community, qualifying it for federal cleanup funds and protections. Cumulative Impact Zone An area where residents are simultaneously exposed to multiple environmental stressors—polluted air, contaminated water, toxic soil—that combine to create a heavier overall health burden than any single pollutant would on its own.
D
Decennial Census The constitutionally mandated count of every person living in the United States, conducted every 10 years by the Census Bureau. Demographics The statistical characteristics of a human population, including age, race, income, language, education, and household composition. Diesel Particulate Matter The fine soot expelled from diesel-burning engines (trucks, buses, ships, generators). Classified as a likely human carcinogen and a major contributor to pollution near highways and ports. Disadvantaged Community A community designated by federal or state government as bearing a heavy combination of environmental, economic, and health burdens, qualifying it for targeted investment under programs like Justice40. Discharge Monitoring Report A required record submitted by facilities holding water discharge permits, documenting the volume and content of pollutants they release into surface waters. Discharge Permit A legal authorization issued by the EPA or a state agency that allows a facility to release a specific pollutant up to a defined limit, usually with monitoring and reporting requirements. Federally known as an NPDES permit for water. Disproportionate Impact A pattern in which one group (often defined by race, income, or geography) suffers significantly more harm from a hazard than the general population, even when overall exposure rates appear similar.
E
EJScreen The EPA's Environmental Justice Screening and Mapping Tool. It overlays environmental burdens (Superfund proximity, traffic, toxic discharges) with demographic vulnerabilities to identify disadvantaged communities. Environmental Justice The principle that all people, regardless of race or income, deserve equal protection from environmental hazards and equal access to a healthy environment. Environmental Protection Agency The U.S. federal agency responsible for setting and enforcing pollution standards for air, water, and soil, and for regulating hazardous chemicals. Environmental Stressor Any factor in the environment—pollution, noise, heat, contaminated water—that contributes to physical or mental health risk. Epidemiology The branch of medicine that studies how often diseases occur in different groups of people and why. Epidemiologists are the disease detectives who investigate outbreaks and clusters.
F
Federal Cleanup Funds Money allocated by Congress (under programs like Superfund, the Inflation Reduction Act, and Justice40) to remediate contaminated land or fund environmental health work in disadvantaged communities. Fenceline Community A neighborhood immediately adjacent to an industrial plant, refinery, or military base. Residents literally share a fence line with the polluter and are the first to be hit by chemical spills, noise, or toxic plumes.
G
Geographic Boundary The defined edges of an area being studied or regulated—often a zip code, census tract, county line, or a custom radius around a polluting facility. Ground-Level Ozone A harmful air pollutant formed when emissions from cars, factories, and chemicals react in sunlight. Different from the protective ozone layer high in the atmosphere—at ground level it triggers asthma and lung damage. Groundwater Water stored in underground aquifers, supplying private wells and many municipal drinking water systems. Once contaminated, it is extremely slow and costly to clean.
H
Hazardous Air Pollutants Also called air toxics. A group of 187+ chemicals known or suspected to cause cancer, birth defects, or other serious health problems—regulated separately from criteria pollutants. Hazardous Substance A chemical, biological, or physical material that poses a risk to human health, property, or the environment. Regulated in the U.S. under laws like CERCLA (Superfund). Health Burden The total impact of a disease or environmental factor on a population, measured in illness, disability, healthcare costs, and lost life expectancy. Home Owners' Loan Corporation A New Deal-era federal agency that produced the original color-coded redlining maps still used today to study how discriminatory housing policy shaped industrial siting.
I
Indigenous Populations Native peoples whose ancestral ties to a place predate the formation of modern nations. In the U.S., this includes federally recognized tribes, Alaska Natives, and Native Hawaiians. Industrial Siting The decision-making process that determines where new factories, refineries, landfills, or hazardous facilities get built. Historically these decisions concentrated polluters in low-income and minority neighborhoods.
J
L
Lead (as pollutant) A toxic heavy metal historically released from leaded gasoline, paint, and industrial smelters. Even tiny amounts cause permanent neurological damage, especially in children. Also a regulated drinking water contaminant. Legal Limit The maximum amount of a pollutant or contaminant that government regulators (like the EPA) allow in air, drinking water, or soil before the area or supply is considered out of compliance with the law. Life Expectancy The average number of years a person born in a given area is expected to live. Differences of 10–20 years between neighboring zip codes often track with environmental and economic conditions. Linguistic Isolation A Census Bureau classification for a household in which no one over age 14 speaks English at least 'very well.' Used as a vulnerability indicator when emergency information is issued only in English. Low-Income Population Households whose income falls below a defined threshold (often a percentage of the federal poverty level), used as a vulnerability marker in environmental justice screening.
M
Maximum Contaminant Level The highest concentration of a specific contaminant that the EPA legally allows in public drinking water. Set per chemical based on health risk and treatment feasibility. Micron A unit of length equal to one-millionth of a meter (10⁻⁶ m). Used to describe filter pore size — the threshold above which particles are mechanically captured. Minority Population In EPA usage, a population whose share of a racial or ethnic minority group is meaningfully higher than that of the surrounding reference population.
N
National Air Toxics Assessment An ongoing EPA review estimating where Americans are exposed to hazardous air pollutants and what cancer and respiratory risks result. National Ambient Air Quality Standards Federal standards set by the EPA that establish the maximum allowable levels of six common air pollutants (the criteria pollutants) considered harmful to public health and the environment. National Emissions Inventory A comprehensive EPA database that estimates air emissions of criteria and hazardous pollutants from every kind of source—industrial, mobile, and natural. National Priorities List The EPA's official list of the most polluted hazardous waste sites in the country, eligible for federal cleanup funding under the Superfund program. Nitrogen Dioxide A reddish-brown toxic gas, primarily a byproduct of vehicle exhaust and power plants. Inflames airways and helps form smog and acid rain. Non-Attainment Area A strict legal designation used by the EPA for an area where measured air quality is worse than the National Ambient Air Quality Standards (NAAQS). Industries operating in these areas face stricter emission regulations. Non-Point Source Pollution that comes from many diffuse sources rather than one identifiable origin—like agricultural runoff, urban stormwater, or atmospheric deposition.
O
Observed vs. Expected Rates An epidemiological method of comparing the actual (observed) number of disease cases in a community against the number that would be expected based on state or national averages. A statistically significant gap suggests an environmental cause. Overburdened Community A term officially adopted by the EPA and state governments to describe minority, low-income, tribal, or indigenous populations that experience a disproportionate amount of environmental harm and health risk compared to the general population.
P
Particulate Matter Microscopic solid particles or liquid droplets suspended in air, including dust, soot, and smoke. PM2.5 (fine particles) is small enough to enter the bloodstream through the lungs. Parts Per Billion A unit 1,000 times more sensitive than parts per million, used for very low concentrations of contaminants. One ppb equals one part pollutant per one billion parts of medium. Parts Per Million A ratio expressing concentration as one unit of solute per million units of solution. For dilute aqueous samples, 1 ppm ≈ 1 mg/L. Percentile A statistical ranking that shows what percentage of a group falls at or below a given value. Being in the 95th percentile for pollution exposure means only 5% of areas are more polluted. Point Source A single, identifiable source of pollution, such as a discharge pipe, smokestack, or factory outlet—the kind regulators can permit and measure directly. Point-Source Pollution Area An area degraded by a single, identifiable source of pollution—such as a specific factory's smokestack or a specific wastewater discharge pipe. Proximity Buffer A mapped zone (often a 1-mile or 3-mile radius) drawn around a hazardous site to define the area of primary impact. Used by regulators to identify which homes and people are most at risk. Public Health The science and practice of protecting and improving the health of whole communities through education, policy, disease surveillance, and environmental regulation.
R
Redlining A historical, federally sanctioned practice (begun by HOLC in the 1930s) of denying mortgages and investment to neighborhoods marked 'hazardous'—usually based on race. Today's most polluted zip codes correlate strongly with the old redlined maps. Refinery An industrial facility that processes crude oil into gasoline, diesel, jet fuel, and other petrochemical products. Refineries are major emitters of benzene, sulfur compounds, and volatile organic chemicals. Reverse Osmosis A pressure-driven filtration process that pushes water through a semipermeable membrane, leaving dissolved minerals, salts, and most contaminants behind in a concentrate stream. Risk Management Plan Facility A facility that handles large quantities of high-risk hazardous chemicals and is required by the EPA to file a public plan describing safety procedures and worst-case spill scenarios.
S
Sacrifice Zone A geographic area that has been permanently impaired or deemed expendable for the sake of broader economic growth or industrial production. These zones almost exclusively impact low-income or minority populations. Self-Reported Data Information reported by the regulated party itself (a factory reporting its own emissions, for example) rather than independently measured. Useful but inherently limited by the reporter's accuracy and honesty. Smokestack A tall industrial chimney that releases combustion gases and pollutants into the air. Often the visible point source for a facility's emissions. Source of Pollution The origin point or activity that introduces a contaminant into the environment. Sources are categorized as point sources (single, identifiable) or non-point sources (diffuse). State Cancer Registry A government-maintained database that tracks every newly diagnosed cancer case in a state, including type and location—essential for spotting cancer clusters. Statistically Significant A finding mathematically unlikely to be the result of random chance or coincidence. Used to confirm that a pattern—like a disease cluster—is real and not just noise in the data. Sulfur Dioxide A toxic gas produced mainly by burning fossil fuels at power plants and industrial facilities. Contributes to acid rain and aggravates respiratory illness. Superfund Site A site in the U.S. so contaminated with hazardous substances that it is placed on the EPA's National Priorities List for long-term federal cleanup. Surface Water Water that sits on top of the land—rivers, lakes, streams, reservoirs. Contrasted with groundwater, which is held underground in aquifers.
T
Total Dissolved Solids The combined concentration of all inorganic and organic substances dissolved in water — minerals, salts, metals, and trace organics — measured in parts per million (ppm). Toxic Plume A spreading cloud or underground flow of contaminants moving away from its source through air, soil, or water. Toxics Release Inventory An EPA database of self-reported releases of specific toxic chemicals to air, water, and land by industrial facilities. Traffic Proximity Data Mapped data on high-volume roadways used to estimate residents' exposure to diesel particulate matter and nitrogen dioxide from freight and passenger vehicles. Tribal Populations Members of federally or state-recognized Native American tribes. Tribal lands are subject to a unique mix of federal, tribal, and sometimes state environmental jurisdiction.