top of page

Glossary of Terms

gradient background.png




A volume of water that covers one acre to a depth of one foot. Equivalent to 43,560 cubic feet or 325,829 gallons.


To determine judicially. To settle by means of a court decision.


The process by which chemicals are held on the surface of a mineral or soil particle.

air stripping

A treatment process used to remove dissolved gases and volatile substances from water, accomplished by bubbling air through the water.


Describes unconsolidated material such as sand, gravel, and silt which has been deposited by flowing water.

appropriative rights

Rights to or ownership of a supply of water which is appropriated, independent of land ownership, and put to beneficial use. Appropriative rights are allocated based on priority of use, and are subject to loss by non-use or abandonment.


An underground formation of rock or sediment which is saturated and sufficiently permeable to transmit economic quantities of water to a well or spring.


best management practices 

Techniques and practices that are accepted as the most effective and practical means to control pollutants or otherwise conserve water resources.


The utilization of living organisms such as bacteria to break down organic contaminants.


See best management practices.


California Environmental Quality Act of 1970

An act that requires public agency decision makers to consider the environmental impacts of a proposed plan.

capital costs

Costs of financing construction and equipment. Capital costs are usually fixed, one-time expenses. Compare operating and maintenance costs.


A substance which tends to produce cancer in a living organism.


See California Environmental Quality Act of 1970.


An Act of Congress, the Comprehensive Environmental Response, Compensation and Liability Act of 1980, which authorizes EPA to manage the cleanup of abandoned or uncontrolled hazardous waste sites. Also known as Superfund.


The application of chlorine to water, generally for the purpose of disinfection.

community water system

A public water system which serves at least 15 service connections used by year-round residents or that regularly serves at least 25 year-round residents. Compare non-community water system.

cone of depression

The depression or drop in water level near a well, resulting from the pumping of that well.

confined aquifer

An aquifer in which ground water is confined or overlain by an impermeable or semi-permeable formation. Compare unconfined aquifer, semi-confined aquifer.

conjunctive use

A program that coordinates the storage of imported surface water supplies in local groundwater basins for future withdrawal and use.

consumptive use

A use of water in which water is removed from available supplies without direct return to a water resource system.


Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil.

cyclic storage

Storage of supplemental water in a groundwater basin for subsequent recovery and use.


Chemical or biological breakdown of a complex compound into simpler compounds.


The biochemical conversion of dissolved nitrate and nitrite nitrogen in soil or water to nitrogen gas.


The removal of dissolved salts, such as sodium chloride, from water.


The movement of suspended or dissolved particles from an area of higher concentration to an area of lower concentration as the result of random movement of individual particles.


The measured drop in water level in or near a well caused by pumping groundwater from the well.



Water or other liquid flowing from a reservoir, basin, or treatment plant.


The U.S. Environmental Protection Agency.


The process of removing particulate matter from water by passing it through a porous medium.

finished water

Water that has been processed in a water treatment plant and is ready for delivery to consumers.

fresh water

Water that contains less than 1,000 mg/l total dissolved solids.


See granular activated carbon adsorption

geophysical log

A detailed description of all underground features discovered during the drilling of a well, including types of formations encountered and their physical characteristics.


Gallons per day, a measure of flow.

granular activated carbon adsorption

Treatment process wherein water is passed through granules of activated carbon. Contaminants such as VOCs adhere to the carbon and are removed from the water.

grey water

Wastewater other than sewage, such as sink, shower, or washing machine drainage.

groundwater, ground water

Water occurring beneath the earth's surface.

groundwater basin

An interconnected permeable geologic formation capable of storing a significant groundwater supply.

hard water

Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from lathering.

hydraulic conductivity

A measure of the rate at which water can move through a permeable medium.

hydraulic gradient

The slope of the water table at a particular point.

hydrologic cycle

The natural process by which water cycles from the atmosphere to the earth (via precipitation), and back to the atmosphere again (via evaporation and other processes).


The study of the occurrence, distribution, circulation, and characteristics of natural waters of the earth.


Describes material or soil that does not allow, or allows only with great difficulty, the movement or passage of water. Compare permeable.

imported water

Water brought into an area from a distant source.

in situ treatment

Water treatment conducted in place, as opposed to removal of the water to another location for treatment.


The flow of water downward from the land surface into and through the upper soil layers.


Water or other liquid flowing into a reservoir, basin, or treatment plant.


Describes material that is of mineral origin. Specifically, describes chemical compounds that do not contain carbon and hydrogen. Compare organic.

instream uses

Water uses that can be carried out without removing the water from its source, such as navigation and recreational uses.


key well

In the San Gabriel Basin, a monitoring well owned by the Los Angeles County Department of Public Works. It is also known as the Baldwin Park key well, for its location in the city of Baldwin Park.


A facility in which solid waste from municipal or industrial sources is disposed.


The liquid that results from water collecting contaminants as it passes through waste materials.

maximum contaminant level

The highest level of a contaminant permissible in water in a public water system.


See maximum contaminant level.


See milligrams per liter.


Million gallons per day, a measure of flow.

milligrams per liter

A measure of concentration of a dissolved substance. A concentration of 1 mg/l means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit of measurement is equivalent to parts per million, or ppm.


Use of mathematical equations to simulate and predict real events and processes.

monitoring well

A well used either to collect water samples for purposes of water quality testing, or to measure groundwater levels.


Memorandum of Understanding.

municipal waste

Waste originating from a community. May be composed of domestic (sewage) and industrial wastewater.

municipal water district

A public entity which supplies water to its member water purveyors.

National Priorities List

A list of high-priority contaminated sites targeted for remedial action by EPA.

non-community water system

A public water system that is not a community water system.

non-point source

A source of pollution that does not have a single point of origin. Pollution from a farmer's field or from urban street runoff falls in this category. Compare point source.


Describes water that may contain objectionable pollution, contamination, minerals, or infective agents and is considered unsafe or unsuitable for drinking. Compare potable.


National Pollutant Discharge Elimination System. Established under the Clean Water Act of 1972, it provides for regulation and monitoring of municipal and industrial waste discharges through a permit system.


See National Priorities List

operable unit

Term for each of a number of separate activities undertaken as part of a Superfund site cleanup.

operation and maintenance costs

The costs of operating a system such as a treatment plant. "O & M" costs are ongoing expenses, such as for repair or for employee salaries. Compare capital costs.


Describes material that originates from plant or animal sources. Specifically, describes chemical compounds containing carbon and hydrogen. Compare inorganic.


See operable unit.


The pumping of water from a groundwater basin in excess of the supply coming into the basin. Such pumping results in continuing depletion of the groundwater and a lowering of the water table.

packed tower aeration

A variation of the air stripping treatment process. Water flows down through packing material, while air flows upward to "strip" VOCs from the water.

parts per million

A measure of concentration of a dissolved substance. Compare milligrams per liter.


A microorganism capable of causing disease.


The slow seepage of water into and through the ground.


Describes the ability of rock or soil to transmit water.


Describes material or soil that allows the movement or passage of water through it. Compare impermeable.


The area occupied by a groundwater contaminant after it has begun to spread, through diffusion or other forces, away from its point of origin.

point source

A stationary source or fixed facility from which pollutants are discharged. Compare non-point source.


Any substance introduced into the environment that adversely affects the usefulness of a resource.

pore space

The space between mineral grains in a porous medium.


Describes water that is safe and satisfactory for drinking and cooking. Compare non-potable water.

Potentially Responsible Party

Any individual or company--including owners, operators, transporters, or generators--potentially responsible for or contributing to a spill or other contamination at a Superfund site.

potentiometric surface

The level to which water will rise in a well that penetrates an aquifer. In an unconfined aquifer, equivalent to the water table.


See parts per million.


Atmospheric moisture, such as rain or snow, that falls to earth.

primary treatment

Initial stage of treatment of wastewater, primarily consisting of removal of settleable solids.

prior appropriation

A doctrine of water law which allocates the right to use water on a first-come, first-served basis.


See Potentially Responsible Party.

public participation plan

A formal plan describing public involvement activities concerning a State-led or State-funded cleanup site.

public water system

A system for the provision to the public of piped water intended for human consumption. Such system must have at least 15 service connections, or regularly serve an average of at least 25 individuals daily for at least 60 days out of the year.


receiving waters

Bodies of water that receive runoff or wastewater discharges, such as streams, rivers, and lakes.


Process by which precipitation or applied water seeps or percolates into the groundwater system.

reclaimed water

Wastewater that has been treated and brought to a level of water quality that makes it suitable for further beneficial use.

remedial action plan

A formal plan of action for cleanup of a contaminated site.


A natural or man-made holding area used to store, regulate, or control water.


Remedial Investigation/Feasibility Study.


Record of Decision.


That part of precipitation, snow melt, or irrigation water that drains or flows off the land into streams or other surface waters.

Safe Drinking Water Act

An Act passed by Congress in 1976 that establishes a cooperative program among local, state, and federal agencies to insure safe drinking water for consumers. It authorizes EPA to set drinking water standards (including maximum contaminant levels), and provides special protection to sole source aquifers.

safe yield

The annual quantity of water that can be taken from a source of supply without depleting the source beyond its ability to be replenished.


The relative concentration of dissolved salts in water.

saturated zone

The area below the water table where all open spaces are filled with water. Compare unsaturated zone.

secondary treatment

Stage of wastewater treatment wherein bacteria are used to break down organic materials and significantly reduce biochemical oxygen demand.

semi-confined aquifer

An aquifer that is partially confined or overlain by a formation of low permeability through which water can pass slowly. Compare confined aquifer, unconfined aquifer.

sole source aquifer

An aquifer that supplies 50 percent or more of the drinking water for an area.

spreading basin, spreading grounds

A man-made basin or series of basins designed to retain water for the purpose of recharging groundwater supplies.

static water level

The elevation or level of water in a well when the pump is not operating.



supplemental water

Imported water brought into an area to supplement local water supplies.

surface water

All water naturally open to the atmosphere, including rivers, streams, lakes, reservoirs, etc.


See total dissolved solids.

tertiary treatment

An advanced stage of wastewater treatment designed to remove nutrients or other constituents remaining after secondary treatment.

Title 22

That portion of the California Administrative Code which requires that producers of drinking water regularly monitor their wells and other sources of supply for various chemical constituents.

total dissolved solids

All of the dissolved solids in a sample of water, measured by evaporating the sample and weighing the residue.


The rate at which water is transmitted through an aquifer.

unconfined aquifer

An aquifer that does not have confining formations or layers. Compare confined aquifer, semi-confined aquifer.

unsaturated zone

The area between the land surface and water table in which pore spaces are not completely filled with water. Also known as the vadose zone. Compare saturated zone.


Underground storage tank.


vadose zone

See unsaturated zone.


See volatile organic compound.

volatile organic compound

One of several organic chemical compounds characterized by the ability to evaporate readily at normal temperatures. Includes various industrial solvents and degreasers such as TCE, PCE, and carbon tetrachloride.


The used water and solids that are the result of domestic or industrial uses of water. Includes municipal waste or sewage.

water purveyor

An agency or person that supplies water.

water supply system

A facility designed for the distribution of potable water, typically including storage tanks and a network of pipes.

water table

The elevation or level of ground water. The upper surface of the saturated zone in an unconfined aquifer.


The land area that drains into a stream. An area that contributes runoff to a specific body of water. Same as drainage basin, hydrologic basin.


A bored, drilled, or driven shaft, or a dug hole, whose purpose is to reach underground water supplies.







bottom of page