The Problem What to Do Rules Resources References Glossary

The Glossary



Absorption -- The process by which ions are taken out of solution to become attached to solid surfaces or integrated into the solid molecular structure.

Acidic -- In water a condition in which the pH is less than 7.

Alluvial -- An adjective referring to alluvium.

Alluvial aquifer -- An aquifer formed by materials deposited by physical processes in river channels and on floodplains.

Alluvium -- Deposits of clay, silt, sand, gravel, or other particulate materials that have been deposited by a stream in a streambed or on a flood plain.

Aquifer -- A geologic formation, which contains sufficient, saturated permeable material to yield significant quantities of water to wells and springs.

Average ground-water velocity -- The speed and direction of travel of ground water through an aquifer. The average ground-water velocity is calculated from the specific discharge and the aquifer porosity.

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Basic -- In water a condition in which the pH is greater than 7.

Batch tests -- Laboratory tests performed on samples of contaminated ground water, aquifer materials, and chemicals in a reactor to evaluate how the chemicals used by a remediation technology might be useful for remediation.

Biodegradable -- A term applied to any substance that can be broken down by organisms.

Borehole -- A cylindrical shaft drilled into the ground using a drilling rig and just large enough in diameter to install a well.

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Capital -- Includes all equipment and infrastructure asociated with a property.

Capture zone -- The area contributing to flow to a well. The shape of the capture zone depends on the average linear ground-water velocity, the rate at which the well is being pumped, and the hydraulic conductivity of the aquifer. The upgradient extent of the capture zone depends on how long the well is being pumped.

Carcinogenic -- A risk of causing cancer posed by an agent external to the reproducing organism.

Chemical reaction kinetics -- The rates and mechanisms by which chemicals react with each other to for products.

Column tests -- Laboratory tests used to investigate the movement of dissolved or suspended solids through aquifer materials.

Concentration -- The amount of contaminant (or other constituent) in a given volume of water, often as milligrams per liter.

Confining layer -- A continuous layer of low-permeability sediment or rock unit that is above or below an aquifer.

Contaminants -- Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to the health of organisms or the ecosystem.

Contamination -- The degradation of natural water quality beyond permissible limits as a result of man's activities. Such limits depend on the potential uses of the water in question.

Contaminant plume -- An elongate zone of moving contaminated water in surface or ground water moving away from the contaminant source.

Cone of depression -- The depression, roughly conical in shape, produced in a water table by the extraction of water from a well at a given rate. The size of the cone of depression depends on the duration of pumping, the pumping rate, and the hydraulic conductivity, specific yield, and thickness of the aquifer.

Cone of impression -- A rise, roughly conical in shape, produced in the water table from the addition of water from an injection well at a rate that is faster than the ability of the aquifer to transmit the water away from the well. The size of the cone of impression depends on the duration of pumping, the pumping rate, and the hydraulic conductivity, specific yield, and thickness of the aquifer.

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Darcy's law -- A mathematical equation stating that the flow rate of water through porous materials is proportional to the hydraulic gradient. The constant of proportionality is the hydraulic conductivity.

Decontamination -- To remove contaminants from water or other objects, such as drilling or sampling equipment.

Discharge -- The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second or gallons per minute.

Drawdown -- The lowering of the water table caused by pumping, measured as the difference between the original water table elevation and the current elevation after a period of pumping.

Driller's log -- A log kept at the time of drilling showing the depth, thickness, ch aracter of the different rock strata penetrated, and location of water-bearing strata.

Drinking-water standard or guideline -- A threshold concentration for a constituent or compound in a public drinking-water supply, designed to protect human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contamination levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.

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Floodplain -- The land bordering a stream, built up of sediments from overflow of the stream during flooding.

Flowpath -- An underground route for ground-water movement, extending from a recharge (intake) zone to a discharge (output) zone such as a shallow stream.

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Gaining stream -- A stream reach in which the water table adjacent to the stream is higher than the water surface in the stream, causing ground water to seep into the stream, increasing its flow.

Ground water -- (1) water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in the pores of geologic materials that make up the Earth's crust.

Ground-water flowpath -- The underground pathway by which ground water moves from areas of recharge to areas of discharge.

Ground-water flow system -- The underground pathways by which ground water moves through several aquifers that are linked together from areas of recharge to areas of discharge.

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Heavy Metals -- Uusually includes the following metals: cadmium, chromium, copper, iron, mangenese, lead, zinc, and nickel.

Heterogeneous -- When used in connection to aquifers, the term means nonuniform becuase the aquifer consists of more than one material type (gravel, sand, silt or clay) distributed as continuous or discontinuous layers.

Hydraulic conductivity -- The capacity of a rock to transmit fresh water, expressed usually as feet per day or meters per second.

Hydraulic gradient -- The slope of the water table which determined as the change in hydraulic head per unit distance in a given direction.

Hydraulic head -- The elevation of the water level in wells penetrating an aquifer and in this case, it is equivalent to the elevation of the water table. Also, the elevation of the water surface in surface water bodies, such as lakes and streams.

Hydrogeology -- The study of the distribution and movement of water through the subsurface environment.

Hydrograph -- A graph of time versus the water-level elevation above sea level or depth to water below surface in a well. The graph is typically used to assess the magnitude of water-level fluctuations or change in an aquifer.

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Impermeable -- Material that does not permit fluids to pass through it.

Impermeable layer -- This is a layer through which water does not pass.

Injection well -- A well used to pump or drain fluids, such as treated water, into an aquifer.

Injection rate -- The rate at which water or fluids are being added to the aquifer through a well.

ion -- an atom or a group of atoms that have lost their electrically neutral status by acquiring or losing one or more electrons The number in he superscript above the chemical symbol indicates the number of electrons gained or lost by the ion. Cations are positively charged ions (such as the hydrogen ion [H+1] or the ferric ion [ Fe+3 ]). Anions are negatively charged ions (such as the chromate ion [ CrO4-2 ].

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Liter (L) -- A volume slightly larger than a quart and equal to approximately 0.26 gallons.

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Maximum Contaminant Level (MCL) -- (1) The greatest amount of a contaminant that can be present in drinking water without causing a risk to human health. (2) Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency. EPA sets MCLs at levels that are economically and technologically feasible. Some states set MCLs which are more strict than EPA's.

Measuring point -- Specific point where data is collected. It is usually marked and has some specific criteria that assure consistent data collection.

Microgram (µg) -- One-millionth of a gram.

Micrograms per liter (µ/L) -- A unit of the concentration of a constituent in water or wastewater. It represents 0.0001 gram of a constituent in 1 liter of water.

Milligram (mg) -- One-thousandth of a gram.

Milligrams per liter (mg/L) -- A unit of the concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1 liter of water.

Monitoring -- (1) Repeated observation, measurement, or sampling at a site, on a scheduled or event basis, for a particular purpose. (2) Testing that water systems must perform to detect and measure contaminants. A water system that does not follow EPA's monitoring methodology or schedule is in violation, and may be subject to legal action.

Monitoring well -- A well designed for measuring water levels and testing ground-water quality.

Mutagenic -- A risk of creating birth defects posed by an agent external to the reproducing organism.

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National Pollutant Discharge Elimination System (NPDES) -- This is a permit system that allows industries and cities to legally discharge treated water to surface water bodies if the fluids being discharged meet US Environmental Protection Agency water quality or other standards.

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Organics -- Shortened term used to refer to manmade organic chemicals made up primarily of carbon, hydrogen, and oxygen. Common examples include pesticides, solvents such as methanol and acetone, and Trichloroethylene (TCE). TCE is a chemical compound that is often used to remove grease and clean metal parts and products.

Oxidizing conditions -- A chemical environment in which oxidation is favorable. Eh values are relative measure of the oxidation potential. Positive values indicate a likelihood of oxidation.

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Particle size -- The diameter, in millimeters, of suspended sediment or bed material. Particle-size classifications are:
    [1] Clay-0.00024-0.004 millimeters (mm);
    [2] Silt-0.004-0.062 mm;
    [3] Sand-0.062-2.0 mm; and
    [4] Gravel-2.0-64.0 mm.

Permeability -- The ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, don't allow water to flow freely.

Permeable -- Capable of transmitting water (porous rock, sediment, or soil).

Permeable layer -- A layer of porous material (rock, soil, unconsolidated sediment); in an aquifer, the layer through which water freely passes as it moves through the ground.

pH -- A measure of the hydrogen ion concentration in water. The range of pH values is from 0 to 14. pH values below 7 are considered to be acidic, whereas pH values above 7 are considered basic. A pH of 7 is neutral.

Plume -- See contaminant plume.

Pollutant -- Any substance that, when present in a hydrologic system at sufficient concentration, degrades water quality in ways that are or could become harmful to human and/or ecological health or that impair the use of water for recreation, agriculture, industry, commerce, or domestic purposes.

Pollution -- An alteration in the character or quality of the environment, or any of its components, that renders it less suited for certain uses. The alteration of the physical, chemical, or biological properties of water by the introduction of any substance that renders the water harmful to use.

Polymer -- A term used to describe large molecules that consist of repeating structural units. These structural units may be organic or inorganic.

Porosity -- The ratio of the pore or void space to the total volume occupied by a material. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer because the pores are usually so small.

Precipitate -- The formation of a solid in a solution resulting from a chemical reaction.

Production well -- A well used to withdraw water or fluids from an aquifer.

Public supply -- Water withdrawn by public governments and agencies, such as a county water department, and by private companies that is then delivered to users. Public suppliers provide water for domestic, commercial, thermoelectric power, industrial, and public water users. Most household water is delivered by a public water supplier. The systems have at least 15 service connections (such as households, businesses, or schools) or regularly serve at least 25 individuals daily for at least 60 days out of the year. There are more than 170,000 public supplies providing water from wells, rivers and other sources to about 250 million Americans. The others drink water from private wells. There are differing standards for public supplies of different sizes and types.

Pump-and-treat method -- This is the most common method of aquifer remediation. Contaminants are removed from the aquifer by means of a production well. They produced water is treated to remove the contaminants and the treated water is returned to either a surface water body or the aquifer.

Pumping rate -- The rate at which water is being withdrawn from an aquifer by a well.

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Recharge -- (1) Water added to an aquifer. (2) Process by which water is added to the zone of saturation to replenish an aquifer.

Redox reactions -- A shorthand term for all chemical reactions in which the atoms have their oxidation number (oxidation state) changed. Oxidation occurs when an atom loses electrons and reduction occurs when an atom gains electrons.

Reducing conditions -- A chemical environment in which reduction is favorable. Eh values are relative measure of the reduction potential. Negative values indicate a likelihood of reduction.

Remediation -- Removal of the source of contamination and treatment of the ground water, the aquifer materials, or both to remove the contaminants in the water.

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Site Characterization Plan -- The blueprint used to develop information about a contaminated site, including the extent and nature of the contamination.

Soil -- The uppermost layer of the Earth's surface, containing unconsolidated rock and mineral particles mixed with organic material.

Soil series -- Soils with similar profiles and they are usually named for a town or geographic place where the soil was first observed and mapped.

Specific conductance -- A measure of the ability of a water to transmit an electric current. The higher the value, the greater ability. Specific conductance is also a measure of the total dissolved solids content of the water. The total dissolved solids in a water is the concentration of all the dissolved ions in water.

Specific discharge -- The volume of water transmitted through a permeable material per unit cross-sectional area calculated from Darcy's law.

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Tailing and rebound -- This occurs near the end of a remediation cycle when most of the contaminant has been removed from the more permeable zones of the aquifer while significant contamination remains in the less permeable parts. The contaminants recovered decrease over time during the cycle to the point where the apparent concentration is below the maximum environmental standard. If remediation ceases, the contaminants in the less permeable part of the aquifer move into the more permeable part, thereby causing the apparent concentration in the ground water to rise above he standard.

Test drilling -- Drilling for exploratory purposes that may or may not include the installation of wells for water sampling and water-level and water-quality determination. Test drilling is also done to provide information of the types and distribution of earth materials below the ground surface and the nature of the layering.

Test holes -- The boreholes drilled during test drilling.

Time-of-travel -- The time required for ground water to move from one point beneath the surface to another.

Toxic -- A health risk (causing death or disease) posed to living organisms by an outside agent.

Treatment zone -- Used in reference to the aquifer volume created by application of the in situ redox manipulation or pump and treat in which the remediation effort has chemically altered the environment or by developed a hydraulic control within a capture zone.

Treatability tests -- Experiments conducted in the laboratory to determine if a specific remediation remedy is likely to be successful.

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Unconfined aquifers -- An aquifer in which the upper boundary is the water table.

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Water quality -- A term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose.

Water quality standard -- Recommended or enforceable maximum contaminant levels of chemicals or materials (such as chlorobenzene, nitrate, iron, arsenic) in water. These levels are established for water used by municipalities, industries, agriculture, and recreationists.

Water sample -- A small volume of water collected from a surface- or ground-water source that is chemically and physically representative of the larger water body.

Water supply -- All of the processes that are involved in obtaining water for the user before use. Includes withdrawal, water treatment, and distribution.

Water table -- (1) The level below the earth's surface at which the ground becomes saturated with water. (2) The top of an unconfined aquifer; indicates the level below which soil and rock are saturated with water.

Water-table Elevation -- The height of the water table above sea level.

Well casing -- The solid piece of pipe that extends from near the ground surface down the well screen and is intended to keep rock, soil, and contaminants from entering the well through the screen.

Well screen -- A perforated interval usually in the lower part of the well casing where ground-water flows into the well when the pump is turned on and a filtering devise used to keep sediment out the well.

Wellfield design -- The layout of production or production and injection wells based on the effects of pumping or injection on the aquifer and the contaminant plume. Pumping/injection rates are usually considered as part of the wellfield design. Placement of the wells is usually governed by the desired effect, such as controlling the movement of a contaminant plume.

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Zone of influence -- The area surrounding an injection well within which the water table has been changed due to recharge caused by the addition of fluids.