CHAPTER 6

GLOSSARY 

accident – An unplanned sequence of events 

resulting in undesirable consequences, such as 

the release of hazardous material to the 

environment. 

active fault – A fault that is likely to have 

another earthquake sometime in the future. 

Faults are commonly considered to be active if 

they have moved one or more times in the last 

10,000 years. In assessing seismic hazard as 

part of the U.S. Geological Survey’s National 

Earthquake Hazard Reduction Program, faults 

for which there is surface evidence of tectonic 

activity during the Quaternary Period are 

considered active. 

acute – Severe but of short duration; not 

chronic. 

Acute Exposure Guideline Levels (AEGLs) – 

Threshold values published by the National 

Research Council and National Academy of 

Sciences for use in chemical emergency 

planning, prevention, and response programs. 

AEGLs represent threshold exposure limits for 

the general population, including susceptible 

individuals, and are developed for exposure 

periods of 10 minutes, 30 minutes, 1 hour, 

4 hours, and 8 hours. AEGL values are defined 

for varying degrees of severity of toxic effects, 

as follows: 

AEGL-1 – The airborne level of concentration 

of a substance above which the exposed 

population could experience notable discomfort, 

irritation, or certain asymptomatic nonsensory 

effects. However, the effects would not be 

disabling and would be transient and reversible 

upon cessation of exposure. 

AEGL-2 – The airborne level of concentration 

of a substance above which the exposed 

population could experience irreversible or other 

serious, long-lasting adverse health effects or an 

impaired ability to escape. 

AEGL-3 – The airborne level of concentration 

of a substance above which the exposed 

population could experience life-threatening 

health effects or death.

air pollutant – Generally, an airborne substance 

that could, in high-enough concentrations, harm 

living things or cause damage to materials. 

From a regulatory perspective, an air pollutant is 

a substance for which emissions or atmospheric 

concentrations are regulated or for which 

maximum guideline levels have been established 

due to potential harmful effects on human health 

and welfare. 

air quality – The cleanliness of the air as 

measured by the levels of pollutants relative to 

the standards or guideline levels established to 

protect human health and welfare. Air quality is 

often expressed in terms of the pollutant for 

which concentrations are the highest percentage 

of a standard (e.g., air quality may be 

unacceptable if the level of one pollutant is 

150 percent of its standard, even if levels of 

other pollutants are well below their respective 

standards). 

air quality control region – Geographic 

subdivisions of the United States designed to 

deal with pollution on a regional or local level. 

Some regions span more than one state. 

alloy – A mixture containing mostly metals. For 

example, brass is an alloy of copper and zinc. 

An amalgam is an alloy (e.g., an amalgam of 

mainly silver and mercury).

alluvium (alluvial) – Unconsolidated, poorly 

sorted detrital sediments, ranging from clay to 

gravel sizes, deposited by streams. 

ambient – Surrounding. 

ambient air – The atmosphere around people, 

plants, and structures. 

ambient air quality standards – Regulations 

prescribing the levels of airborne pollutants that 

may not be exceeded during a specified time in a 

defined area. 

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6–2

American Indian Religious Freedom Act of 

1978 – An act that protects and preserves for 

American Indians their traditional religious 

rights, including the rights of access to religious 

sites, use and possession of sacred objects, and 

worship through traditional ceremonies and 

rites. 

anthropogenic – Caused or produced by 

humans. 

aquatic – Living or growing in, on, or near 

water. 

aquifer – An underground geologic formation, 

group of formations, or part of a formation 

capable of yielding a significant amount of water 

to wells or springs. 

aquitard – A relatively less permeable geologic 

unit that inhibits the flow of water. 

Archaeological Resources Protection Act of 

1979 – An act protecting cultural resources on 

federally owned lands. This act requires a 

permit for archaeological excavations or the 

removal of any archaeological resources on 

public or American Indian lands. It also 

prohibits interstate or foreign trafficking in 

cultural resources taken in violation of state or 

local laws and requires Federal agencies to 

develop plans for surveying lands under their 

control. 

archaeological site – Any location where 

humans have altered the terrain or discarded 

artifacts during prehistoric or historic times. 

artifact – An object produced or shaped by 

human beings and of archaeological or historic 

interest. 

artisanal gold mining – A general term used in 

reference to small-scale mining operations 

prevalent in some developing countries that 

employ the crude and highly polluting process of 

mixing mercury with sediments from river 

bottoms and adjacent areas to extract gold. 

atmospheric dispersion – The distribution of 

pollutants from their source into the atmosphere 

by wind, turbulent air motion attributable to 

solar heating of Earth’s surface, or air movement 

over rough terrain and variable land and water 

surfaces. 

attainment area – An area considered to have 

air quality as good as or better than the National 

Ambient Air Quality Standards for a given 

pollutant. An area may be in attainment for one 

pollutant and nonattaining for others. (See also 

nonattainment area.) 

basalt – The most common volcanic rock, dark 

gray to black in color, high in iron and 

magnesium and low in silica. It is typically 

found in lava flows. 

baseline – A quantitative expression of 

conditions, costs, schedule, or technical progress 

that constitutes the standard against which to 

measure the performance of an effort. For 

National Environmental Policy Act evaluations, 

baseline is defined as the existing environmental 

conditions against which impacts of the 

proposed action and its alternatives can be 

compared. The environmental baseline is the 

site environmental conditions as they exist or are 

estimated to exist in the absence of the proposed 

action. 

basin – Geologically, a circular or elliptical 

downwarp or depression in the Earth’s surface 

that collects sediment. Younger sedimentary 

beds occur in the center of basins. 

Topographically, a depression into which water 

from the surrounding area drains. 

bedding plane – Surface separating layers of 

sedimentary rocks and deposits. Each bedding 

plane marks the termination of one deposit and 

the beginning of another of different character, 

such as a surface separating a sandstone bed 

from an overlying mudstone bed. Rock tends to 

break or separate readily along bedding planes. 

bedrock – The solid rock that lies beneath soil 

and other loose surface materials. 

bioaccumulation – The accumulation or 

buildup of contaminants in living systems by 

biological processes. Methylmercury can 

bioaccumulate in animal tissue.

bioaccumulation factor – The ratio of the 

concentration of a chemical in an organism to its 
Glossary

6–3

concentration in a medium to which the 

organism is exposed. 

bound – An analysis of impacts or risks such 

that the result overestimates or describes a limit 

on (i.e., “bounds”) potential impacts or risks. 

bounding analysis – An analysis designed to 

overestimate or determine an upper limit to 

potential impacts or risks. 

cancer – The name given to a group of diseases 

characterized by uncontrolled cellular growth 

where the cells have invasive characteristics that 

enable the disease to transfer from one organ to 

another. 

carbon dioxide – A colorless, odorless, 

nonpoisonous gas that is a normal component of 

the ambient air and an expiration product of 

normal animal life. 

carbon monoxide – A common air pollutant 

formed by incomplete combustion; a colorless, 

odorless gas that is toxic if breathed in high 

concentrations over an extended period; when 

humans are exposed to lower concentrations, it 

can result in chronic effects. 

carbonate – A sedimentary rock made mainly 

of calcium carbonate (CaCO3). Limestone and 

dolomite are common carbonate sedimentary 

rocks. (See dolomite and limestone.) 

carcinogen – A substance or agent that produces 

or incites cancerous growth. 

Carolina bay – A closed, elliptical-shaped 

depression capable of holding water; a type of 

wetland. 

chronic – Lasting for a long period or marked 

by frequent recurrence. 

Class I area – A specifically designated area 

where the degradation of air quality is 

stringently restricted (e.g., many national parks, 

wilderness areas). (See Prevention of 

Significant Deterioration.) 

Class II area – Most of the country that is not 

designated as Class I is designated as Class II. 

Class II areas are generally cleaner than air 

quality standards require, and moderate 

increases in new pollution are allowed after a 

regulatory-mandated impacts review. 

clay – The name for a family of finely 

crystalline sheet silicate minerals that commonly 

form as a product of rock weathering. Also, any 

soil particle smaller than or equal to about 

0.002 millimeters (0.00008 inches) in diameter. 

Clean Air Act – An act mandating and 

providing for the enforcement of regulations to 

control air pollution from various sources. 

Clean Air Act Amendments of 1990 – 

Amendments expanding the U.S. Environmental 

Protection Agency’s enforcement powers and 

adding restrictions on air toxics, ozone-depleting 

chemicals, stationary and mobile emission 

sources, and emissions implicated in acid rain 

and global warming. 

Code of Federal Regulations – A publication in 

codified form of all Federal regulations in force. 

colluvium (colluvial) – A loose deposit of rock 

debris accumulated at the base of a cliff or slope. 

confined aquifer – A permeable geologic unit 

bounded above and below by aquitards and 

containing water at a pressure higher than 

atmospheric pressure. 

conformity – As defined in the Clean Air Act, 

“the nation’s compliance with an 

implementation plan’s purpose of eliminating or 

reducing the severity and number of violations 

of the National Ambient Air Quality Standards 

and achieving expeditious attainment of such 

standards. Activities in conformity will not 

(1) cause or contribute to any new violation of 

any standard in any area, (2) increase the 

frequency or severity of any existing violation of 

any standard in any area, or (3) delay timely 

attainment of any standard or any required 

interim emission reduction or other milestones 

in any area.” 

conglomerate – A sedimentary rock made of 

rounded rock fragments, such as pebbles, 

cobbles, and boulders, in a finer-grained matrix. 

To be classified as a conglomerate, some of the 

constituent pebbles must be at least about 

2 millimeters (one-thirteenth of 1 inch) across. 
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6–4

criteria pollutants – An air pollutant that is 

regulated by National Ambient Air Quality 

Standards. The U.S. Environmental Protection 

Agency must describe the characteristics and 

potential health and welfare effects that form the 

basis for setting, or revising, the standard for 

each regulated pollutant. Criteria pollutants 

include sulfur dioxide, nitrogen dioxide, carbon 

monoxide, ozone, lead, and two size classes of 

particulate matter, less than 10 micrometers 

(0.0004 inch) in diameter, and less than 

2.5 micrometers (0.0001 inch) in diameter. New 

pollutants may be added to, or removed from, 

the list of criteria pollutants as more information 

becomes available. (See National Ambient Air 

Quality Standards.) Note: Sometimes pollutants 

regulated by state laws are also called criteria 

pollutants.

critical habitat – Habitat essential to the 

conservation of an endangered or threatened 

species that has been designated as critical by 

the U.S. Fish and Wildlife Service or the 

National Marine Fisheries Service following the 

procedures outlined in the Endangered Species 

Act and its implementing regulations 

(50 CFR 424). (See endangered species and 

threatened species.) 

The lists of critical habitats can be found in 

Title 50 of the Code of Federal Regulations, 

Sections 17.95 (fish and wildlife) and 

17.96 (plants), and in Part 226 (marine species). 

cultural resources – Archaeological sites, 

architectural features, historic resources, 

traditional-use areas, and American Indian 

sacred sites. 

cumulative impacts – Impacts on the 

environment that result when the incremental 

impact of a proposed action is added to the 

impacts from other past, present, and reasonably 

foreseeable future actions regardless of what 

agency (Federal or non-Federal) or person 

undertakes the other actions. Cumulative 

impacts can result from individually minor but 

collectively significant actions taking place over 

a period of time. 

day-night average sound level – The 24-hour, 

A-weighted equivalent sound level expressed in 

decibels. A 10-decibel penalty is added to sound 

levels between 10:00 P.M. and 7:00 A.M. to 

account for increased annoyance due to noise 

during night hours. 

decibel – A unit for expressing the relative 

intensity of sounds on a logarithmic scale from 

zero for the average least perceptible sound to 

about 130 for the average level at which sound 

causes pain to humans. For traffic and industrial 

noise measurements, the A-weighted decibel, a 

frequency-weighted noise unit, is widely used. 

The A-weighted decibel scale corresponds 

approximately to the frequency response of the 

human ear and thus correlates well with 

loudness. 

decibel, A-weighted – A unit of sound 

measurement that incorporates a metering 

characteristic and the “A” weighting specified 

by the American National Standards Institute in 

S1.4–1983 (R 2001) to account for the 

frequency response of the human ear. 

decontamination – The removal of chemical 

contamination from facilities, equipment, or 

soils by washing, heating, chemical or 

electrochemical action, mechanical cleaning, or 

other techniques. 

deposition – In geology, the laying down of 

potential rock-forming materials; sedimentation. 

In atmospheric transport, the settling out on 

ground and building surfaces of atmospheric 

aerosols and particles (“dry deposition”) or their 

removal from the air to the ground by 

precipitation (“wet deposition”). 

dip – A measure of the angle between the flat 

horizon and the slope of a sedimentary layer, 

fault plane, metamorphic foliation, or other 

geologic structure. 

discharge – In surface-water hydrology, the 

amount of water issuing from a spring or in a 

stream that passes a specific point in a given 

period of time. 

dolomite – A mineral composed of calciummagnesium-carbonate (CaMg[CO3]2) that is the 

chief constituent of a sedimentary rock 

commonly called dolomite, as well as of some 

kinds of marble. It is thought to form by the 
Glossary

6–5

alteration of limestone by seawater. (See 

carbonate.) 

drainage basin – The land area drained by a 

particular stream. 

drinking water standards – The level of 

constituents or characteristics in a drinking 

water supply specified in regulations under the 

Safe Drinking Water Act as the maximum 

permissible. 

earthquake – A sudden ground motion or 

vibration of the Earth. It can be produced by a 

rapid release of stored-up energy along an active 

fault. 

ecology – A branch of science dealing with the 

interrelationships of living organisms with one 

another and with their nonliving environment. 

ecosystem – A community of organisms and 

their physical environment interacting as an 

ecological unit. 

effluent – A waste stream flowing into the 

atmosphere, surface water, groundwater, or soil. 

endangered species – Plants or animals that are 

in danger of extinction through all or a 

significant portion of their ranges and that have 

been listed as endangered by the U.S. Fish and 

Wildlife Service or the National Marine 

Fisheries Service, following the procedures 

outlined in the Endangered Species Act and its 

implementing regulations (50 CFR 424). (See 

threatened species.) The lists of endangered 

species can be found in Title 50 of the Code of 

Federal Regulations, Sections 17.11 (wildlife), 

17.12 (plants), and 222.23(a) (marine 

organisms). 

Endangered Species Act of 1973 – An act 

requiring Federal agencies, with the consultation 

and assistance of the Secretaries of the Interior 

and Commerce, to ensure that their actions will 

not likely jeopardize the continued existence of 

any endangered or threatened species or 

adversely affect the habitat of such species. 

environmental assessment (EA) – A concise 

public document that a Federal agency prepares 

under the National Environmental Policy Act 

(NEPA) to provide sufficient evidence and 

analysis to determine whether a proposed 

agency action would require preparation of an 

environmental impact statement (EIS) or a 

Finding of No Significant Impact. A Federal 

agency may also prepare an EA to aid its 

compliance with NEPA when no EIS is 

necessary or to facilitate preparation of an EIS 

when one is necessary. An EA must include 

brief discussions of the need for the proposal, 

alternatives, environmental impacts of the 

proposed action and alternatives, and a list of 

agencies and persons consulted. (See Finding of 

No Significant Impact, environmental impact 

statement, and National Environmental Policy 

Act.) 

environmental impact statement – The 

detailed written statement that is required by 

Section 102(2)(C) of the National 

Environmental Policy Act (NEPA) for a 

proposed major Federal action significantly 

affecting the quality of the human environment. 

A U.S. Department of Energy (DOE) EIS is 

prepared in accordance with applicable 

requirements of the Council on Environmental 

Quality NEPA regulations in Title 40 of the 

Code of Federal Regulations (CFR), 

Parts 1500–1508, and DOE NEPA regulations in 

Title 10 of the CFR, Part 1021. The statement 

includes, among other information, discussions 

of the environmental impacts of the proposed 

action and all reasonable alternatives, adverse 

environmental effects that cannot be avoided 

should the proposal be implemented, the 

relationship between short-term uses of the 

human environment and enhancement of 

long-term productivity, and any irreversible and 

irretrievable commitments of resources. 

environmental justice – The fair treatment and 

meaningful involvement of all people regardless 

of race, color, national origin, or income with 

respect to the development, implementation, and 

enforcement of environmental laws, regulations, 

and policies. Fair treatment means that no group 

of people, including racial, ethnic, or 

socioeconomic groups, should bear a 

disproportionate share of the negative 

environmental consequences resulting from 

industrial, municipal, or commercial operations 

or the execution of Federal, state, local, or tribal 
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6–6

programs and policies. Executive Order 12898 

directs federal agencies to make achieving 

environmental justice part of their missions by 

identifying and addressing disproportionately 

high and adverse effects of agency programs, 

policies, and activities on minority and lowincome populations. (See minority population 

and low-income population.) 

epicenter – The point on the Earth’s surface 

directly above the focus of an earthquake. 

erosion – Removal of material by water, wind, 

or ice. 

exposure – The condition of being subject to the 

effects of, or acquiring a dose of, a potential 

stressor such as a hazardous chemical agent; 

also, the process by which an organism acquires 

a dose of a chemical such as mercury. Exposure 

can be quantified as the amount of the agent 

available at various boundaries of the organism 

(e.g., skin, lungs, gut) and available for 

absorption. 

exposure limit – The level of exposure to a 

hazardous chemical (set by law or a standard) at 

which or below which adverse human health 

effects are not expected to occur. (See reference 

concentration and reference dose.) 

exposure pathway – The course a chemical or 

physical agent takes from the source to the 

exposed organism. An exposure pathway 

describes a mechanism by which chemicals or 

physical agents at or originating from a release 

site reach an individual or population. Each 

exposure pathway includes a source or release 

from a source, an exposure route, and an 

exposure point. If the exposure point differs 

from the source, the transport/exposure medium 

such as air or water is also included. 

(See exposure.) 

Farmland Protection Policy Act – An act 

whose purpose is to reduce the conversion of 

farmland to nonagricultural uses as a result of 

Federal projects and programs. The act requires 

that Federal agencies comply to the fullest extent 

possible with state and local government 

policies to preserve farmland. It includes a 

recommendation that evaluations and analyses 

of prospective farmland conversion impacts be 

made early in the planning process—before a 

site or design is selected—and that, where 

possible, agencies make such evaluations and 

analyses part of the National Environmental 

Policy Act process. 

fault – A fracture or a zone of fractures within a 

rock formation along which vertical, horizontal, 

or transverse slippage has occurred. A normal 

fault occurs when the hanging wall has been 

depressed in relation to the footwall. A reverse 

fault occurs when the hanging wall has been 

raised in relation to the footwall. 

Finding of No Significant Impact – A public 

document issued by a Federal agency briefly 

presenting the reasons why an action for which 

the agency has prepared an environmental 

assessment has no potential to have a significant 

effect on the human environment and, thus, will 

not require preparation of an environmental 

impact statement. (See environmental 

assessment and environmental impact 

statement.) 

flask – A container used to store mercury. 

Mercury storage flasks, typically made of 

0.5-centimeter-thick (0.2-inch-thick) low-carbon 

steel, can hold 34.6 kilograms (76 pounds) of 

mercury and are sealed with a threaded plug. A 

typical mercury storage flask is similar in size 

and dimensions to a 3-liter soda bottle. 

floodplain – The lowlands and relatively flat 

areas adjoining inland and coastal waters and the 

flood-prone areas of offshore islands. 

Floodplains include, at a minimum, that area 

with at least a 1.0 percent chance of being 

inundated by a flood in any given year. 

The base floodplain is defined as the area that 

has a 1.0 percent or greater chance of being 

flooded in any given year. Such a flood is 

known as a 100-year flood. 

The critical action floodplain is defined as the 

area that has at least a 0.2 percent chance of 

being flooded in any given year. Such a flood is 

known as a 500-year flood. 

The probable maximum flood is the hypothetical 

flood considered to be the most severe 

reasonably possible flood, based on the 
Glossary

6–7

comprehensive hydrometeorological application 

of maximum precipitation and other 

hydrological factors favorable for maximum 

flood runoff (e.g., sequential storms and 

snowmelts). It is usually several times larger 

than the maximum recorded flood. 

formation – In geology, the primary unit of 

formal stratigraphic mapping or description. 

Most formations possess certain distinctive 

features. 

fracture – Any break in rock along which no 

significant movement has occurred. 

geology – The science that deals with the Earth: 

the materials, processes, environments, and 

history of the planet, including rocks and their 

formation and structure. 

global climate change – Changes in the Earth’s 

surface temperature thought to be caused by the 

greenhouse effect and responsible for changes in 

global climate patterns. The greenhouse effect 

is the trapping and buildup of heat in the 

atmosphere (troposphere) near the Earth’s 

surface. Some of the heat flowing back toward 

space from the Earth’s surface is absorbed by 

water vapor, carbon dioxide, ozone, and several 

other gases in the atmosphere and then 

reradiated back toward the Earth’s surface. 

groundwater – Water below the ground surface 

in a zone of saturation. It usually occurs in 

aquifers that may supply wells and springs, as 

well as baseflow, to major streams and rivers. 

Hazard Index – (ecological definition) The sum 

of the individual Hazard Quotients of 

constituents within a class that exert effects with 

the same toxicological mechanism or endpoint 

and are additive in effect.

Hazard Index – (human health definition) A 

summation of the Hazard Quotients for all 

chemicals now being used at a site, as well as 

those proposed to be added, to yield the 

cumulative levels for the site. A Hazard Index 

value of 1.0 or less means that no adverse 

human health effects (noncancer) are expected 

to occur. (See Hazard Quotient.) 

Hazard Quotient – The value used as an 

assessment of non-cancer-associated toxic 

effects of chemicals, e.g., kidney or liver 

dysfunction. It is a ratio of the estimated 

exposure to that level of exposure at which it is 

expected that adverse health effects would begin 

to be produced. It is independent of a cancer 

risk, which is calculated for only those 

chemicals identified as carcinogens.

hazardous air pollutants – Air pollutants not 

covered by National Ambient Air Quality 

Standards but which may present a threat of 

adverse human health or environmental effects. 

Those specifically listed in Title 40 of the Code 

of Federal Regulations, Section 61.01, are 

asbestos, benzene, beryllium, coke oven 

emissions, inorganic arsenic, mercury, 

radionuclides, and vinyl chloride. More broadly, 

hazardous air pollutants are any of the 

188 pollutants to be regulated or reviewed under 

Section 112(b) of the Clean Air Act. Very 

generally, hazardous air pollutants are any air 

pollutants that may realistically be expected to 

pose a threat to human health or welfare. 

hazardous chemical – Under Title 29 of the 

Code of Federal Regulations, Part 1910, 

Subpart Z, hazardous chemicals are defined as 

“any chemical that is a physical hazard or a 

health hazard.” Physical hazards include 

combustible liquids, compressed gases, 

explosives, flammables, organic peroxides, 

oxidizers, pyrophorics, and reactives. A health 

hazard is any chemical for which there is good 

evidence that acute or chronic health effects 

occur in exposed employees. Hazardous 

chemicals include carcinogens, toxic or highly 

toxic agents, reproductive toxins, irritants, 

corrosives, sensitizers, hepatotoxins, 

nephrotoxins, agents that act on the 

hematopoietic system, and agents that damage 

the lungs, skin, eyes, or mucous membranes. 

hazardous material – A material, including a 

hazardous substance as defined by Title 49 of 

the Code of Federal Regulations, Section 171.8, 

that poses a risk to health, safety, and property 

when transported or handled. 

hazardous waste – A category of waste 

regulated under the Resource Conservation and 

Recovery Act (RCRA). To be considered 
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6–8

hazardous, a waste must be a solid waste under 

RCRA and must exhibit at least one of four 

characteristics described in Title 40 of the Code 

of Federal Regulations, Sections 261.20 through 

261.24 (i.e., ignitability, corrosivity, reactivity, 

or toxicity) or be specifically listed by the U.S. 

Environmental Protection Agency in 

Sections 261.31 through 261.33. 

historic resources – Archaeological sites, 

architectural structures, and objects dating from 

1492 or later, after the arrival of the first 

Europeans to the Americas. 

infrastructure – The basic facilities, services, 

and utilities needed for the functioning of an 

industrial facility. Transportation and electrical 

systems are part of the infrastructure. 

interbedded – Occurring between beds (layers) 

or lying in a bed parallel to other beds of a 

different material. 

interim status – Period during which treatment, 

storage, and disposal facilities subject to the 

Resource Conservation and Recovery Act are 

temporarily allowed to operate while awaiting 

the issuance or denial of a permanent permit. 

labor force – All persons of a defined 

geographic area classified as employed or 

unemployed. 

lacustrine – Relating to lakes, as in lacustrine 

sediments. 

land use – A characterization of land surface in 

terms of its potential utility for various activities. 

lava – Molten rock (magma) that reaches the 

Earth’s surface through a volcanic eruption. 

When cooled and solidified, forms extrusive 

(volcanic) igneous rock. 

limestone – A sedimentary rock composed 

mostly of the mineral calcite, CaCO3. (See 

carbonate.) 

loam – Soil material that is composed of 7 to 

27 percent clay particles, 28 to 50 percent silt 

particles, and less than 52 percent sand particles. 

local magnitude – See magnitude.

low-income individuals/persons – Individuals 

whose income is less than the poverty threshold 

defined in the U.S. Bureau of the Census’ 

Current Population Reports, Series P-60 on 

Income and Poverty. 

low-income population – Low-income 

populations, defined in terms of U.S. Census 

Bureau annual statistical poverty levels (Current 

Population Reports, Series P-60 on Income and 

Poverty), may consist of groups or individuals 

who live in geographic proximity to one another 

or who are geographically dispersed or transient 

(such as migrant workers or American Indians), 

where either type of group experiences common 

conditions of environmental exposure or effect. 

(See environmental justice and minority 

population.) 

magnitude – A number that reflects the relative 

strength or size of an earthquake. Magnitude is 

based on the logarithmic measurement of the 

maximum motion recorded by a seismograph. 

An increase of one unit of magnitude (for 

example, from 4.6 to 5.6) represents a 10-fold 

increase in wave amplitude on a seismograph 

recording or approximately a 30-fold increase in 

the energy released. Several scales have been 

defined, but the most commonly used are 

(1) local magnitude (ML), commonly referred to 

as “Richter magnitude,” (2) surface-wave 

magnitude (Ms), and (3) body-wave magnitude 

(Mb). Each is valid for a particular type of 

seismic signal varying by such factors as 

frequency and distance. These magnitude scales 

will yield approximately the same value for any 

given earthquake within each scale’s respective 

range of validity. A fourth scale (moment 

magnitude [Mw]) is the latest to be applied that 

better estimates the size of very large 

earthquakes that the other scales underestimate 

by varying degrees. 

maximally exposed individual – A 

hypothetical individual whose location and 

habits result in the highest total radiological or 

chemical exposure (and thus dose) from a 

particular source for all exposure routes 

(e.g., inhalation, ingestion, direct exposure). 
Glossary

6–9

megawatt – A unit of power equal to 

1 million watts. Megawatt-thermal is commonly 

used to define heat produced, while megawattelectric defines electricity produced. 

mercury (elemental) – Elemental mercury is a 

dense, naturally occurring, silver-colored 

metallic element that is liquid at room 

temperature. Sometimes called “quicksilver,” 

liquid mercury has been used extensively in 

manufacturing processes because it conducts 

electricity, reacts to temperature changes, and 

alloys with many other metals. 

mercury (primary) – Unused, ‘virgin’ mercury 

that has been produced as the main product of 

mining activities. 

mercury (secondary) – Mercury recycled from 

the dismantling of used products or equipment. 

meteorology – The science dealing with the 

atmosphere and its phenomena, especially as 

relating to weather. 

migration – The natural movement of a material 

through the air, soil, or groundwater; also, 

seasonal movement of animals from one area to 

another. 

Migratory Bird Treaty Act – An act making it 

unlawful, except in connection with permitted 

activities, to pursue, take, attempt to take, 

capture, possess, or kill any migratory bird, or 

any part, nest, or egg of any such bird. 

minority individuals – Individuals who identify 

themselves as a member of the following 

population groups: American Indian or Alaska 

Native; Asian; black or African American; 

Hispanic or Latino; Native Hawaiian or other 

Pacific Islander; or multiracial minority (two or 

more races, at least one of which is a minority 

race under Council on Environmental Quality 

guidelines). This definition is similar to that 

given in the Council on Environmental Quality’s 

environmental justice guidance; however, it has 

been modified to reflect revisions to the 

Standards for the Classification of Federal Data 

on Race and Ethnicity (62 FR 58782 through 

58790), which is published by the Office of 

Management and Budget. 

minority population – Minority populations 

exist where either: (a) the minority population of 

the affected area exceeds 50 percent or (b) the 

minority population percentage of the affected 

area is meaningfully greater than in the general 

population or other appropriate unit of 

geographic analysis (such as a governing body’s 

jurisdiction, a neighborhood, census tract, or 

other similar unit). Minority refers to 

individuals who are members of the following 

population groups: American Indian or Alaskan 

Native; Asian or Pacific Islander; Black, not of 

Hispanic origin; or Hispanic. Minority 

populations include either a single minority 

group or the total of all minority persons in the 

affected area. They may consist of groups of 

individuals living in geographic proximity to 

one another or a geographically 

dispersed/transient set of individuals (such as 

migrant workers or American Indians), where 

either type of group experiences common 

conditions of environmental exposure or effect. 

(See environmental justice and low-income 

population.) 

Mississippian – A period of the Paleozoic Era 

spanning the time between about 360 and 

320 million years ago (following the Devonian 

Period and preceding the Pennsylvanian Period). 

mitigation – actions taken to lessen the impacts 

of a proposed action, including (1) avoiding an 

impact altogether by not taking a certain action 

or parts of an action; (2) minimizing impacts by 

limiting the degree or magnitude of an action 

and its implementation; (3) rectifying an impact 

by repairing, rehabilitating, or restoring the 

affected environment; (4) reducing or 

eliminating the impact over time by preservation 

and maintenance operations during the life of an 

action; or (5) compensating for an impact by 

replacing or providing substitute resources or 

environments. 

Modified Mercalli Intensity – A level on the 

modified Mercalli scale. A measure of the 

perceived intensity of earthquake ground 

shaking with 12 divisions, from I (not felt by 

people) to XII (damage nearly total). It is a 

unitless expression of observed effects. 

mudstone – A detrital sedimentary rock 

composed of clay-sized particles. 
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National Ambient Air Quality Standards – 

Standards defining the highest allowable levels 

of certain pollutants in the ambient air (i.e., the 

outdoor air to which the public has access). 

Because the U.S. Environmental Protection 

Agency must establish the criteria for setting 

these standards, the regulated pollutants are 

called criteria pollutants. Criteria pollutants 

include sulfur dioxide, nitrogen dioxide, carbon 

monoxide, ozone, lead, and two size classes of 

particulate matter, less than 10 micrometers 

(0.0004 inch) in diameter, and less than 

2.5 micrometers (0.0001 inch) in diameter. 

Primary standards are established to protect 

public health; secondary standards are 

established to protect public welfare 

(e.g., visibility, crops, animals, buildings). 

(See criteria pollutant.) 

National Emission Standards for Hazardous 

Air Pollutants (NESHAPs) – Emission 

standards set by the U.S. Environmental 

Protection Agency for air pollutants that are not 

covered by National Ambient Air Quality 

Standards and may, at sufficiently high levels, 

cause increased fatalities, irreversible health 

effects, or incapacitating illness. These 

standards are given in Title 40 of the Code of 

Federal Regulations, Parts 61 and 63. 

NESHAPs are given for many specific 

categories of sources (e.g., equipment leaks, 

industrial process cooling towers, drycleaning 

facilities, petroleum refineries). (See hazardous 

air pollutants.)

National Environmental Policy Act of 1969

(NEPA) – NEPA is the basic national charter for 

protection of the environment. It establishes 

policy, sets goals (in Section 101), and provides 

means (in Section 102) for carrying out the 

policy. Section 102(2) contains action-forcing 

provisions to ensure that Federal agencies follow 

the letter and spirit of the Act. For major 

Federal actions significantly affecting the quality 

of the human environment, Section 102(2)(C) of 

NEPA requires Federal agencies to prepare a 

detailed statement that includes the 

environmental impacts of the proposed action 

and other specified information. 

National Historic Preservation Act of 1966, as 

amended – An act providing that property 

resources with significant national historic value 

be placed in the National Register of Historic 

Places. It does not require permits; rather, it 

mandates consultation with the proper agencies 

whenever it is determined that a proposed action 

might impact a historic property. 

National Pollutant Discharge Elimination 

System (NPDES) – A provision of the Clean 

Water Act that prohibits discharge of pollutants 

into waters of the United States unless a special 

permit is issued by the U.S. Environmental 

Protection Agency, a state, or, where delegated, 

a tribal government on an American Indian 

reservation. The NPDES permit lists either 

permissible discharges, the level of cleanup 

technology required for wastewater, or both. 

National Register of Historic Places 

(NRHP) – The official list of the Nation’s 

cultural resources that are worthy of 

preservation. The National Park Service 

maintains the list under direction of the 

Secretary of the Interior. Buildings, structures, 

objects, sites, and districts are included in the 

NRHP for their importance in American history, 

architecture, archaeology, culture, or 

engineering. Properties included in the NRHP 

range from large-scale, monumentally 

proportioned buildings to smaller-scale, 

regionally distinctive buildings. The listed 

properties are not just of nationwide importance; 

most are significant primarily at the state or 

local level. Procedures for listing properties in 

the NRHP are found in Title 36 of the Code of 

Federal Regulations, Part 60. 

Native American Graves and Repatriation 

Act of 1990 – An act established to protect 

American Indian graves and associated funerary 

objects. This act requires Federal agencies and 

museums to inventory human remains and 

associated funerary objects, to provide culturally 

affiliated tribes with the documented results of 

that inventory, and to return, on request, items in 

the inventory to the culturally affiliated tribes. 

natural phenomena hazard – A category of 

events (e.g., earthquake, wind, flood, and 

lightning) that must be considered in the U.S. 

Department of Energy (DOE) facility design, 

construction, and operations, as specified in 

DOE Order 420.1B. 
Glossary

6–11

nitrogen oxides – The oxides of nitrogen, 

primarily nitrogen oxide and nitrogen dioxide, 

produced in the combustion of fossil fuels. 

Nitrogen dioxide emissions constitute an air 

pollution problem, as they contribute to acid 

deposition and the formation of atmospheric 

ozone. 

noise – Undesirable sound that interferes or 

interacts negatively with the human or natural 

environment. Noise may disrupt normal 

activities (e.g., hearing, sleep), damage hearing, 

or diminish the quality of the environment. 

nonattainment area – An area that the 

U.S. Environmental Protection Agency has 

designated as not meeting (i.e., not being in 

attainment of) one or more of the National 

Ambient Air Quality Standards for sulfur 

dioxide, nitrogen dioxide, carbon monoxide, 

ozone, lead, and particulate matter. An area may 

be in attainment for some pollutants, but not for 

others. 

outfall – The discharge point of a drain, sewer, 

or pipe into or that eventually leads to a body of 

water. 

ozone – The triatomic form of oxygen; in the 

stratosphere, ozone protects the Earth from the 

sun’s ultraviolet rays, but in lower levels of the 

atmosphere, ozone is considered an air pollutant. 

pallet – A small platform on which material is 

stored. Pallets are often constructed of wood 

and serve to lift the material off the ground to 

keep it dry. Pallets also enable the material to be 

easily lifted with a forklift. 

particulate matter (PM) – Any finely divided 

solid or liquid material, other than uncombined 

(i.e., pure) water. A subscript denotes the upper 

limit of the diameter of particles included. Thus, 

PM10 includes only those particles equal to or 

less than 10 micrometers (0.0004 inch) in 

diameter; PM2.5 includes only those particles 

equal to or less than 2.5 micrometers 

(0.0001 inch) in diameter. Total suspended 

particulates were first used as the indicator of 

particulate concentrations. 

peak ground acceleration – A measure of the 

maximum horizontal acceleration (as a 

percentage of the acceleration due to Earth’s 

gravity) experienced by a particle on the surface 

of the Earth during the course of earthquake 

motion. 

Pennsylvanian – A geologic period of the 

Paleozoic Era spanning the time between about 

320 and 286 million years ago. The 

Pennsylvanian may be best known for its coalbearing deposits that originated from vast 

swamps that were present at the time, as well as 

the formation of the Appalachian Mountains 

from the collision of present-day Europe and 

North America with present-day Africa and 

South America. 

percent g – In measuring earthquake ground 

motion, the acceleration (the rate of change in 

velocity) experienced relative to that due to 

Earth’s gravity (i.e., 9.8 meters per square 

second). 

perched aquifer/groundwater – A body of 

groundwater of small lateral dimensions 

separated from an underlying body of 

groundwater by an unsaturated zone. 

permeability – The ability of a rock, soil, or 

other material to allow water to flow through its 

interconnected spaces. 

persistence – The resistance to degradation as 

measured by the period of time required for 

complete decomposition of a material.

pH – A numeric value that indicates the relative 

acidity or alkalinity of a substance on a scale of 

0 to 14, with the neutral point at 7.0. Acid 

solutions have pH values lower than 7.0, and 

basic (alkaline) solutions have values higher 

than 7.0. 

plume – The elongated pattern of contaminated 

air or water originating at a point source such as 

a smokestack or hazardous waste disposal site. 

PM2.5 and PM10 – See particulate matter.

potable water – Water that is fit to drink. 
Draft Long-Term Management and Storage of Elemental Mercury Environmental Impact Statement 

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prehistoric – Predating written history; in North 

America, also predating contact with Europeans. 

Prevention of Significant Deterioration – 

Regulations required by the 1977 Clean Air Act 

amendments to limit increases in criteria air 

pollutant concentrations above baseline in areas 

that already meet the National Ambient Air 

Quality Standards. Cumulative increases in 

pollutant levels after specified baseline dates 

must not exceed specified maximum allowable 

amounts. These allowable increases, also 

known as increments, are especially stringent in 

areas designated as Class I areas (e.g., national 

parks, wilderness areas) where the preservation 

of clean air is particularly important. All areas 

not designated as Class I are currently 

designated as Class II. Maximum increments in 

pollutant levels are also given in Title 40 of the 

Code of Federal Regulations, Section 51.166, 

for Class III areas, if any such areas should be so 

designated by the U.S. Environmental Protection 

Agency. Class III increments are less stringent 

than those for Class I or Class II areas. (See 

National Ambient Air Quality Standards.)

prime farmland – As defined in Title 7 of the 

Code of Federal Regulations, Section 657.5(a), 

“Prime farmland is land that has the best 

combination of physical and chemical 

characteristics for producing food, feed, forage, 

fiber, and oilseed crops, and is also available for 

these uses (the land could be cropland, 

pastureland, rangeland, forest land, or other 

land, but not urban built-up land or water). It has 

the soil quality, growing season, and moisture 

supply needed to economically produce 

sustained high yields of crops when treated and 

managed, including water management, 

according to acceptable farming methods.” Soil 

mapping units that qualify as prime farmland 

within each state are identified by the U.S. 

Department of Agriculture, National Resources 

Conservation Service State Conservationists. 

Quaternary – The second geologic period of 

the Cenozoic Era, dating from about 1.6 million 

years ago to the present. It contains two epochs: 

the Pleistocene and the Holocene. It is 

characterized by the first appearance of human 

beings on Earth. 

Record of Decision – A document providing a 

concise public record of an agency’s decision on 

a proposed action for which an environmental 

impact statement was prepared. Prepared in 

accordance with Title 40 of the Code of Federal 

Regulations, Section 1505.2, the Record of 

Decision identifies the alternatives considered in 

reaching the decision, the environmentally 

preferable alternative, factors balanced by the 

agency in making the decision, whether all 

practicable means to avoid or minimize 

environmental harm have been adopted, and if 

not, why they have not. 

reference concentration – The chronic 

exposure concentration for a given hazardous 

chemical at which or below which adverse 

human noncancer health effects are not expected 

to occur. (See exposure limit and reference 

dose.) 

reference dose – The chronic exposure dose for 

a given hazardous chemical at which or below 

which adverse human noncancer health effects 

are not expected to occur. (See exposure limit

and reference concentration.)

reflasking – The transfer of mercury from 

aging, damaged, or leaking 34.6-kilogram 

(76-pound) flasks to new 34.6-kilogram 

(76-pound) steel flasks. 

region of influence – A site-specific geographic 

area. The regions of influence for different 

resources can vary widely in extent. For 

example, the region of influence for ecological 

resources would generally be confined to the site 

and nearby adjacent areas, whereas the 

socioeconomic region of influence would 

include the cities and counties surrounding each 

site that could be affected by the proposed 

action. 

Resource Conservation and Recovery Act 

(RCRA), as amended – This law gives the 

U.S. Environmental Protection Agency the 

authority to control hazardous waste from 

“cradle to grave” (i.e., from the point of 

generation to the point of ultimate disposal), 

including its minimization, generation, 

transportation, treatment, storage, and disposal. 

RCRA also sets forth a framework for 
Glossary

6–13

management of nonhazardous solid waste. 

(See hazardous waste.) 

Richter magnitude – See magnitude. 

rift – A valley caused by extension of the 

Earth’s crust. Its floor forms as a portion of the 

crust moves downward along normal faults. 

risk – The probability of a detrimental effect 

from exposure to a hazard. Risk is often 

expressed quantitatively as the probability of an 

adverse event occurring multiplied by the 

consequence of that event (i.e., the product of 

these two factors). However, separate 

presentation of probability and consequence is 

often more informative. 

risk assessment (chemical) – The qualitative 

and quantitative evaluation performed to define 

the risk posed to human health and/or the 

environment by the presence or potential 

presence and/or use of specific chemical 

materials. 

runoff – The portion of rainfall, melted snow, or 

irrigation water that flows across the ground and 

which may eventually enter surface waters. 

sand – Loose grains of rock or mineral sediment 

formed by weathering that range in size 

from 0.0625 to 2.0 millimeters (0.0025 to 

0.08 inches) in diameter and often consist of 

quartz particles. 

sandstone – A sedimentary rock composed 

mostly of sand-size particles cemented usually 

by calcite, silica, or iron oxide. 

sanitary waste (wastewater) – Wastes 

generated by normal housekeeping activities, 

liquid or solid (includes sludge), that are not 

hazardous or radioactive. 

scoping – An early and open process for 

determining the scope of issues to be addressed 

in an environmental impact statement and for 

identifying the significant issues related to a 

proposed action. 

sedimentary rock – Rock formed from the 

accumulation of sediment, which may consist of 

fragments and mineral grains of varying sizes 

from pre-existing rocks, remains or products of 

animals and plants, products of chemical action, 

or mixtures of these. Sedimentary rocks often 

have distinctive layering or bedding. 

seismic – Pertaining to any earth vibration, 

especially that of an earthquake. 

seismicity – The frequency and distribution of 

earthquakes. 

sewage – The total nonhazardous organic waste 

and wastewater generated by an industrial 

establishment or a community. 

sewer – A pipe or conduit (sewer) intended to 

carry wastewater or waterborne wastes from 

homes, businesses, and industries to a treatment 

facility. 

shale – Sedimentary rock derived from mud, 

commonly finely laminated (bedded). Particles 

in shale are commonly clay minerals mixed with 

tiny grains of quartz eroded from pre-existing 

rocks. “Shaley” means like a shale or having 

some shale component, as in shaley sandstone. 

silt – Loose particles of rock or mineral 

sediment that range in size from about 0.002 to 

0.0625 millimeters (0.00008 to 0.0025 inches) in 

diameter. Silt is finer than sand, but coarser than 

clay. 

siltstone – A fine-grained sedimentary rock 

composed mostly of silt-sized grains. 

socioeconomics – Demographic and economic 

characteristics of a defined geographic area. 

soils – All unconsolidated materials above 

bedrock. Natural earthy materials on the Earth’s 

surface, in places modified or even made by 

human activity, containing living matter, and 

supporting or capable of supporting plants. 

sole-source aquifer – A designation granted by 

the U.S. Environmental Protection Agency 

when groundwater from a specific aquifer 

supplies at least 50 percent of the drinking water 

for the area overlying the aquifer. Sole-source 

aquifers have no alternative source or 

combination of sources that could physically, 

legally, and economically supply all those who 

obtain their drinking water from the aquifer. 
Draft Long-Term Management and Storage of Elemental Mercury Environmental Impact Statement 

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solid waste – In general, solid wastes are 

non-liquid, non-soluble discarded materials 

ranging from municipal garbage to industrial 

wastes that contain complex and sometimes 

hazardous substances. Solid wastes include 

sewage sludge, agricultural refuse, demolition 

wastes, and mining residues.

For purposes of regulation under the Resource 

Conservation and Recovery Act, solid waste is 

any garbage; refuse; sludge from a waste 

treatment plant, water supply treatment plant, or 

air pollution control facility; and other discarded 

material. Solid waste includes solid, liquid, 

semisolid, or contained gaseous material 

resulting from industrial, commercial, mining, 

and agricultural operations and from community 

activities. A more-detailed regulatory definition 

of solid waste can be found in Title 40 of the 

Code of Federal Regulations, Section 261.2. 

(See hazardous waste and Resource 

Conservation and Recovery Act.) 

spill prevention, control, and 

countermeasures plan – A plan prepared by a 

facility to minimize the likelihood of a spill and 

to expedite control and cleanup activities should 

a spill occur. 

stabilize – To convert a compound, mixture, or 

solution to a nonreactive form. 

State Historic Preservation Officer – The state 

officer charged with the identification and 

protection of prehistoric and historic resources 

in accordance with the National Historic 

Preservation Act. 

stormwater – Stormwater runoff, snowmelt 

runoff, and surface runoff and drainage. 

sulfur oxides – Common air pollutants, 

primarily sulfur dioxide, a heavy, pungent, 

colorless gas (formed in the combustion of fossil 

fuels, considered a major air pollutant), and 

sulfur trioxide. Sulfur dioxide is involved in the 

formation of acid rain. It can also irritate the 

upper respiratory tract and cause lung damage. 

surface water – All bodies of water on the 

surface of the Earth and open to the atmosphere, 

such as rivers, lakes, reservoirs, ponds, seas, and 

estuaries. 

tectonic – Of or relating to motion in the Earth’s 

crust and occurring on geologic faults. 

threatened species – Any plants or animals that 

are likely to become endangered species within 

the foreseeable future throughout all or a 

significant portion of their ranges and that have 

been listed as threatened by the U.S. Fish and 

Wildlife Service or the National Marine 

Fisheries Service, following the procedures set 

out in the Endangered Species Act and its 

implementing regulations (50 CFR 424). 

(See endangered species.) The lists of threatened 

species can be found in Title 50 of the Code of 

Federal Regulations, Sections 17.11 (wildlife), 

17.12 (plants), and 227.4 (marine organisms). 

Note: Some states also list species as threatened. 

Thus, in certain cases a state definition would 

also be appropriate.

toxic – Poisonous (to living organisms); capable 

of producing disease or otherwise harmful to 

human health when taken into the body. 

Mercury is toxic.

Toxic Substances Control Act (TSCA) – This 

law requires that the health and environmental 

effects of all new chemicals be reviewed by the 

U.S. Environmental Protection Agency before 

they are manufactured for commercial purposes. 

This act also imposes strict limitations on the 

use and disposal of polychlorinated biphenyls, 

chlorofluoro-carbons, asbestos, dioxins, certain 

metal-working fluids, and hexavalent chromium. 

In addition, the provisions of the Mercury 

Export Ban Act relating to the prohibition on 

sale, distribution, or transfer of elemental 

mercury by federal agencies, and to the 

prohibition on the export of elemental mercury, 

amended Sections 6 and 12, respectively of 

TSCA. 

toxicity reference value – An exposure level 

from a valid scientific study that represents a 

threshold for some level of ecological effect. 

traditional cultural property – A property or 

place that is eligible for inclusion in the National 

Register of Historic Places because of its 

association with cultural practices and beliefs 

that are (1) rooted in the history of a community 

and (2) important to maintaining the continuity 
Glossary

6–15

of that community’s traditional beliefs and 

practices. 

treatment – Under the Resource Conservation 

and Recovery Act, any method, technique, or 

process designed to change the physical, 

chemical, or biological character or composition 

of any hazardous waste. 

unemployment rate – The number of 

unemployed persons as a percentage of the labor 

force. 

viewshed – The extent of the area that may be 

viewed from a particular location. Viewsheds 

are generally bounded by topographic features 

such as hills or mountains. 

visual resource management – A process 

devised by the U.S. Bureau of Land 

Management to assess the aesthetic quality of a 

landscape, and, consistent with the results of that 

analysis, to so design proposed activities as to 

minimize their visual impact on the landscape. 

The process consists of a rating of visual quality 

followed by a measurement of the degree of 

contrast between proposed development 

activities and the existing landscape. Four 

classifications are employed to describe different 

degrees of modification to landscape elements: 

Class I, areas where the natural landscape is 

preserved, including national wilderness areas 

and the wild sections of national wild and scenic 

rivers; Class II, areas with very limited land 

development activity, resulting in visual 

contrasts that are seen but do not attract 

attention; Class III, areas in which development 

may attract attention, but the natural landscape 

still dominates; and Class IV, areas in which 

development activities may dominate the view 

and may be the major focus in the landscape. 

volatile organic compound – Any of a broad 

range of organic compounds, often halogenated, 

that vaporize at ambient or relatively low 

temperatures, such as benzene, chloroform, and 

methyl alcohol. In regard to air pollution, any 

organic compound that participates in 

atmospheric photochemical reaction, except for 

those determined by the U.S. Environmental 

Protection Agency Administrator to have 

negligible photochemical reactivity.

wastewater – Water originating from human 

sanitary water use (domestic wastewater) and 

from a variety of industrial processes (industrial 

wastewater). 

water quality standards and criteria – Limits 

on the concentrations of specific constituents or 

on the characteristics of water, often based on 

water use classifications (for example, drinking 

water, recreation, propagation of fish and 

aquatic life, agricultural and industrial use). 

Water quality standards are legally enforceable, 

whereas water quality criteria are 

nonenforceable recommendations based on 

biotic impacts. 

water table – The boundary between the 

unsaturated zone and the deeper, saturated zone. 

The upper surface of an unconfined aquifer.

wetlands – Areas that are inundated or saturated 

by surface water or groundwater and that 

typically support vegetation adapted for life in 

saturated soils. Wetlands generally include 

swamps, marshes, bogs, and similar areas 

(e.g., sloughs, potholes, wet meadows, river 

overflow areas, mudflats, natural ponds).