Glossary of Groundwater Terms
The following terms appear frequently in groundwater discussions:
| Alluvium | sediments consisting of silt, sand, clay, and gravel in varying proportions that are deposited by flowing water in marshes or valleys |
| Aquifer | a saturated geologic formation (rock or sediment) capable of storing, transmitting and yielding reasonable amounts of groundwater to wells and springs |
| Artesian Aquifer | See Confined Aquifer below. |
| Artesian Well | a vertical bore hole in which a pipe-like structure is inserted into the ground so that it withdraws water from a confined aquifer (artesian aquifer) |
| Attenuation | the soil's ability to lessen the amount of, or reduce the severity of groundwater contamination; "during attenuation, the soil holds essential plant nutrients for uptake by agronomic crops, immobilizes metals that might be contained in municipal sewage sludge, or removes bacteria contained in animal or human wastes. 18" |
| Baseflow | the sustained flow (amount of water) in a stream
that comes from groundwater discharge or seepage.
Groundwater flows underground until the water table intersects the land surface and the flowing water becomes surface water in the form of springs, streams/rivers, lakes and wetlands. Baseflow is the continual contribution of groundwater to rivers and is important source of flow between rainstorms. Groundwater continues to discharge as baseflow because of the new recharge of rainwater in the landscape. |
| Bedrock | solid or fractured rock usually underlying unconsolidated geologic materials; bedrock may be exposed at the land surface |
| Capillary Fringe | saturated zone immediately above the water table where saturation is maintain by capillary tension exerted by soil pores |
| Condensation | the process by which water or other liquids change from gas vapor to a liquid; process that occurs when water droplets form on surfaces or around the nuclei of a particle |
| Cone of Depression | the zone (around a well in an unconfined aquifer) that is normally saturated, but becomes unsaturated as a well is pumped; an area where the water table dips down forming a "V" or cone shape due to a pumping well |
| Confined Aquifer (artesian aquifer) | an aquifer holding water under pressure by a layer above it that does not allow water to pass through. Due to pressure, the water level of a well in a confined aquifer will rise above the top of the aquifer. |
| Confining
Layer (aquitard or aquifuge) |
geologic material with little or no permeability or hydraulic conductivity. Water does not pass through this layer or the rate of movement is extremely slow. |
| Contaminant (pollutant) | any substance that makes water unfit for a given use |
| Cubic Feet per Second (cfs) | the volume of water in cubic feet (one-foot cube) that passes a given point in one second of time; USGS uses this measurement in reporting streamflow values |
| Discharge Area | an area where groundwater emerges at the surface; an area where upward pressure or hydraulic head moves groundwater towards the surface to escape as a spring, seep, or baseflow of a stream |
| Drainage Basin | the land area from which surface runoff drains into a stream or lake |
| Evaporation | the process by which water or other liquids change from liquids to a gas vapor; evaporation can return infiltrated water to the atmosphere from upper soil layers before it reaches groundwater or surface water, and occur from leaf surfaces (interception), water bodies (lakes, streams, wetlands, oceans), small puddled depressions in the landscape. |
| Evapotranspiration | the sum of evaporation plus transpiration |
| Feet per Second (ft/sec) | the distance in feet that an object or water moves downstream in one second of time; a small twig floats downstream at about 1-2 ft/sec |
| Filtering | the soil's ability to attenuate substances which includes retaining chemicals or dissolved substances on the soil particle surface, transforming chemicals through microbial biological processing, retarding movement, as well as capturing solid particles. |
| Flow System | groundwater flow from the recharge area to a discharge area; three levels of regional, intermediate, and local. In a regional flow system, the recharge area is at the basin or watershed divide and the discharge area is at a river in the valley bottom. In a local flow system, the recharge area is at a topographical high spot and the discharge area is at a nearby topographical low spot. |
| Geology | the study of science dealing with the origin, history, materials and structure of the earth, together with the forces and process operating to produce change within and on the earth |
| Glacial Drift | sediment transported or deposited by glaciers or the water melting from a glacier |
| Glacial Outwash | well-sorted sand, or sand and gravel deposited by water melting from a glacier |
| Groundwater | the water below the water table contained in void spaces (pore spaces between rock and soil particles, or bedrock fractures) |
| Groundwater Basin | the underground area from which groundwater drains. The basins could be separated by geologic or hydrologic boundaries. |
| Groundwater Divide | the boundary between two adjacent groundwater basins, which is represented by a high point in the water table |
| Hydraulic Conductivity | the term used to describe the permeability of water through a medium; a controlling factor on the rate at which water can move through a permeable medium |
| Hydraulic
Head (head) |
the energy that causes groundwater to flow; the total mechanical energy per unit weight; the sum of the elevation head and the pressure head |
| Hydrogeology | the study of the interrelationships of geologic materials and processes with water, especially groundwater |
| Hydrology | the study of the occurrence, distribution, and chemistry of all waters of the earth |
| Impermeable | not allowing water to pass through |
| Infiltration | the process of water moving from the ground surface vertically downward into the soil |
| Interception Loss | precipitation that is intercepted by trees, vegetation, and/or buildings and evaporates quickly back into the atmosphere before reaching the ground. |
| Interflow (subsurface stormflow) | water that travels laterally or horizontally through the zone of aeration (vadose zone) during or immediately after a precipitation event and discharges into a stream or other body of water |
| Leachate | a liquid formed by water percolating through soil or soluble waste as in a landfill |
| Leaching | the natural process by which water transports salts and other soluble materials through the soil |
| Maximum Contaminant Level (MCL) | the highest concentration of a substance permissible in public drinking water supply as determined by the EPA (Environmental Protection Agency) |
| Micrograms per Liter (ug/l) | a measure of the amount of dissolved solids in a solution in terms of micrograms of solid per liter of solution; Equivalent to part per billion in water or 1ug/l=1ppb |
| Milligrams per Liter (mg/l) | a measure of the amount of dissolved solids in a solution in terms of milligrams of solid per liter of solution; Equivalent to part per million in water or 1mg/l=1ppm |
| Monitoring Well |
a non-pumping well, generally of small diameter, that is used to measure the elevation of a water table or water quality. A piezometer is one type of monitoring well. |
| Moraine | an accumulation of earth and stones carried by a glacier and usually deposited into a high point like a ridge |
| Municipal Well (public or community well) | a pumping well that serves water to more than 25 people for at least 60 days of the year |
| Nitrate (NO3) | a chemical formed when nitrogen from ammonia (NH3), ammonium (NH4) and other nitrogen sources combines with oxygenated water |
| Non-point Source Pollution | pollution from dispersed sources like agricultural activities, urban runoff, and atmospheric deposition |
| Part per Billion (ppb) | a measure of the amount of dissolved solids in a solution in terms of a ratio between the number of parts of solids to a billion parts of total volume; Equivalent to microgram per liter in water or 1ppb=1 ug/l |
| Part per Million (ppm) | a measure of the amount of dissolved solids in a solution in terms of a ratio between the number of parts of solids to a million parts of total volume; Equivalent to milligram per liter in water or 1ppm=1 mg/l |
| Perched Aquifer | a saturated zone with in the zone of aeration that overlies a confining layer; a perched aquifer is above the main water table. |
| Percolation | the actual movement of subsurface water either horizontally or vertically; lateral movement of water in the soil subsurface toward nearby surface drainage feature (e.g. stream) or vertical movement through the soil to groundwater zone. |
| Permeability | the property or capacity of a soil or rock for transmitting a fluid, usually water; the rate at which a fluid can move through a medium |
| Pesticides | chemicals including insecticides, fungicides, and herbicides that are used to kill living organisms |
| Piezometer | a type of monitoring well that is open only at the top and bottom of its casing |
| Plume | an underground pattern of contaminant concentrations created by the movement of groundwater beneath a contaminant source. Contaminants spread mostly laterally in the direction of groundwater movement. The spill/source site is the highest concentration, and the concentration decreases away from the source. |
| Point Source Pollution | pollution from distinct sources, such as industrial discharge pipes, underground storage tanks, septic systems, or spills |
| Porosity | the ratio of the volume of void or air spaces in a rock or sediment to the total volume of the rock or sediment |
| Potable | water safe for drinking |
| Potentiometric Surface | an imaginary surface that represents the level to which water rises in wells in a confined aquifer; (similar to the water table of an unconfined aquifer) |
| Precipitation | deposition of rain, snow, sleet, dew, frost, fog, or hail |
| Private Well | a pumping well that serves one home or is maintained by a private owner |
| Quantity of groundwater | the amount of groundwater stored in an aquifer that is available for use |
| Recharge Area | an area in which water infiltrates and moves downward into the zone of saturation of an aquifer; area that replenishes groundwater |
| Runoff-Direct | the sum of surface runoff and interflow |
| Runoff-Surface (overland flow) | precipitation that cannot be absorbed by the soil because the soil is already saturated with water (saturation excess overland flow); precipitation that exceeds infiltration; the portion of rain, snow melt, irrigation water, or other water that moves across the land surface and enters a wetland, stream, or other body of water (overland flow). Overland flow usually occurs in urban settings (pavement, roofs, etc.) or where the soils are very fine textured or heavily compacted. |
| Runoff-Total | includes the sum of surface runoff (overland flow), baseflow, and interflow (subsurface stormflow) that moves across or through the land and enters a stream or other body of water. |
| Septic System-conventional (private onsite wastewater treatment system [POWTS]) | used to treat household sewage and wastewater by allowing the solids to decompose and settle in a tank, then letting the liquid be absorbed by the soil in a drainage field |
| Spring | a natural discharge of groundwater at the land's surface |
| Stemflow | water that is intercepted by vegetation and then runs down plant stems or tree trunks to the soil surface |
| Surface Water | water found in ponds, lakes, streams, rivers, and inland seas |
| Throughfall | water that is intercepted by vegetation and then drips off it to reach the soil surface |
| Till | glacier deposits composed primarily of unsorted sand, silt, clay, and boulders laid down directly by the melting ice |
| Topographic Divide | a high point in the land surface that provides a boundary between adjacent watersheds or basins |
| Topography | the contour of the land surface; the arrangement of the land surface including its relief and the position of its natural and man-made features |
| Toxin | a poisonous compound that causes certain diseases or health problems |
| Transpiration | the process by which plants take up water through their roots and then give off water vapor through their leaves (open stomata) |
| Unconfined Aquifer (water table aquifer) | an aquifer with continuous layers of permeable soil and rock that extends from the land surface to the base of the aquifer. The water table forms the upper boundary of the aquifer. |
| Watershed | the land area from which surface water and groundwater drains into a stream system; the area of land that generates total runoff (surface flow, interflow, and baseflow) for a particular stream system |
| Water Cycle (hydrologic cycle) | the continuous circulation of water from the atmosphere to the earth and back to the atmosphere including condensation, precipitation, runoff, groundwater, evaporation, and transpiration |
| Water Table | the water surface in an unconfined aquifer; the level below which the pore spaces in the soil or rock are saturated with water; the upper surface of the zone of saturation |
| Water Table Contour | a line in a groundwater map that connects points of equal groundwater elevation |
| Well | a vertical bore hole in which a pipe-like structure is inserted into the ground in order to discharge (pump) water from an aquifer |
| Zone of Aeration (vadose zone or unsaturated zone) | the zone between the land surface and the water table in which the pore spaces between soil and rock particles contain water, air, and/or other gases |
| Zone of Saturation (saturated zone) | the zone in which the pore spaces between soil and rock particles are completely filled with water. The water table is the top of the zone of saturation |