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activated sludge

mass of living bacterial organisms feeding on waste material that is settled; is recycled to aeration tank


waste matter carried away in sewers or drains

secondary sewage treatment

The second level of raw sewage treatment is secondary sewage treatment—a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable, oxygen-demanding organic wastes.

in-stream uses

Use of water withought removing from its source for activities eg. fishing, hydroelectric power


an impermeable body of rock that may contain water but does not allow transmission of water through it


a way of supplying water to an area of land


Deposits of fine solids that settle out from wastewater during the treatment process.


a body of rock or sediment that stores groundwater and allows the flow of groundwater

storm-water runoff

consists of water volumes that are created during precipitation events and flow over surfaces into sewer systems or receiving waters; all precipitation waters that leave project site boundaries on the surface are considered.


a slab of impervious surface at the bottom of an aquifer that does not allow water to go through

nonpoint source

Source of pollution that is indistinct and hard to follow, such as runoff

tertiary sewage treatment

removal of nutrients and traces of toxic organic material from sewage by additional treatment processes

artesian wells

wells from which pressurized water flows to the surface

point source

A specific source of pollution that can be identified, such as a pipe.

thermal pollution

harm to lakes and rivers resulting from the release of excessive waste heat into them

biochemical oxygen demand

amount of oxygen required for biochemical decomposition process


The percentage of the total volume of a rock or sediment that consists of open spaces.

potable water

safe water to drink

unconfined aquifer

aquifer in which there is no impermeable layer restricting the upper surface of the zone of saturation

confined aquifer

A groundwater storage area trapped between two impermeable layers of rock.

primary sewage treatment

Mechanical sewage treatment in which large solids are filtered out by screens and suspended solids settle out as sludge in a sedimentation tank

water diversion

movement of water from surface water or groundwater over some distance to its point to use


process by which a body of water becomes too rich in dissolved nutrients, leading to plant growth that depletes oxygen


water that flows over the ground surface rather than soaking into the ground


The evaporation of water from soil plus the transpiration of water from plants.


The condition in which the salt content of soil accumulates over time to above normal levels; occurs in some parts of the world where water containing high salt concentration evaporates from fields irrigated with standing water.

fecal coliform bacteria

Bacteria found in the intestinal tracts of warm-blooded animals. Organisms used as an indicator of pollution and possible presence of waterborne pathogens

saltwater intrusion

Movement of salt water into freshwater aquifers in coastal and inland areas as groundwater is withdrawn faster than it is recharged by precipitation.


water that fills the cracks and spaces in underground soil and rock layers

groundwater mining

a condition that occurs as aquifers are frequently pumped beyond their flow and air charge capacities.

hydrologic cycle

the natural process by which water is purified and made fresh through evaporation and precipitation. The cycle provides all the fresh water available for biological life.

clean water act

Federal Law setting a national goal of making all natural surface water fit for fishing and swimming by 1983, banned polluted discharge into surface water and required the metals be removed from waste

safe drinking water act

set maximum contaminant levels for pollutants that may have adverse effects on human health

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