GLOSSARY OF TERMS EXTRACTED BY M.S.N. CARPENTER FOLLOWING TRANSLATION OF "WATER WELLS" (author: Michel DETAY, English language edition published by Masson-Wiley, 1997).
379 keywords in bold;
Syn: synonyms; alternative forms and variants separated by commas;
Abbr: abbreviations or short forms; e.g.: specific examples; 290 definitions tagged with Ð; contexts in italics; explanations and technical notes in roman type;
Well development can be monitored by absorption tests ,
(cf. Lugeon test).
Ð The process of introducing acid down a well into a water-bearing formation,
in order to dissolve part of the carbonate clogging material or rock constituents. It
is also used to remove mud injected during drilling. The general objective of
acidization is to increase the discharge capacity by improving the
permeability, (also known as acidization or acid treatment).
Ð Quantity of chlorine available for a given reaction.
(cf. chlorimetic titre).
active management of groundwaters
Ð Planned control of aquifers involving actions to improve quantity and quality of abstracted waters.
Ð Compounds added during acidization in order to maintain iron and aluminium
oxides in solution, (e.g. Rochelle salts, citric acid, lactic acid, ammonium
Ð Auxiliary chemical substance serving to assist or contribute
to a reaction. Acid pyrophosphate may be used following treatment of the
medium or the product with an adjuvant that raises its pH (e.g. caustic soda
or sodium carbonate).
Ð Said of an environment in which oxygen (or air) is present, of organisms
requiring oxygen for growth or a process that can only take place in the
presence of oxygen
Ð The progessive change in material properties with increased age; in
catchment structures, usually marked by a deterioration caused by clogging
air-lift pumping Syn: air-lift development
Ð The most commonly used and most efficient method of well development; air
supplied via a line is injected from the base of a tube submerged in the water
well. The emulsion created in this way reduces the density of the water
contained in the tube.
alkalimetric titre Abbr: AT, (cf. alkalinity).
Ð Sum of the concentrations of hydroxides, carbonates and bicarbonates of the
alkali metals and alkaline earths present in a given solution. The alkalinity
of a solution is a measure of its ability to neutralize acidity. On the basis
of the alkalimetric titre or the total alkalimetric titre, it is possible to
derive the proportions of the three main groups of chemical species that give
rise to alkalinity (c.f. alkalimetric titre, total alkalimetric titre).
Includes activity due to alpha-emitting actinides such as 239-Pu and 241-Am,
but radon is excluded from the definition of overall alpha-emitter radioactivity
given by the ICRP, (c.f. radionuclide, beta-emitter radioactivity).
e.g. plutonium isotopes.
Ð Method of well development, which consists of alternating sudden stops and
starts in order to create brief and powerful variations of pressure on the
water-bearing layer, thus reversing the flow through the screen. This
procedure, also known as rawhiding, facilitates the disruption of sand
bridging, but there is a risk of wear and tear of the pumping equipment, (cf.
Ð An ion NH
from ammonia by combination with a
hydrogen ion or atom, occurring in salts having properties that ressemble the
alkali metals, and also in quaternary ammonium compounds.
The ammonium ion is very frequently present in groundwaters, resulting in most
cases from the anaerobic decomposition of nitrogenous organic matter ,
(cf. quaternary ammonia compounds).
Ð Said of an environment in which oxygen (or air) is absent, of organisms only
able to grow in the absence of oxygen or a process that can only take place in
the absence of oxygen.
Ð Device for automatic recording of data in analogue form, e.g. water level
pressure transducer system. Measurements from chart recorders need to be
digitized prior to data treatment and interpretation, (cf. electronic data recorder).
annulus Syn: annular space
Ð Cylindrical zone surrounding a borehole, used in the estimation of
quantities required for the chemical treatment of a well.
Ð A body of relatively impermeable rock that is capable of absorbing water
slowly but does not transmit it rapidly enough to supply a well or spring.
Aquiclude or semi-permeable terrains show very slow circulation (also known as
confining bed, aquitard).
aquifer Syn: aquiferous formation
Ð Permeable hydrological formation which allows significant discharge of
groundwaters as well as the capture of appreciable amounts of water by
economical means. An aquifer can be defined in terms of the reservoir, the
hydrodynamic, hydrochemical and hydrobiological mechanisms, the part of the
global water cycle involved, as well as the spatial and temporal variability
of these characteristics. The aquifer is recharged by effective infiltration,
i.e. the amount of water actually reaching the groundwater body, whereas its
geometry depends on the characteristics of the geological and hydrodynamic
boundaries, (cf. groundwater body).
Ð Operation designed to improve well performance by enhancing the transmissive
properties of the aquifer; similar to well development, except that the fine
fraction of the aquifer itself is removed (c.f. well development, mechanical
Ð Reduction of hydraulic head in the immediate vicinity of the well due to
mechanical clogging, (cf. well losses).
1. (adj.) Said of a geological formation or layer with very low hydraulic
(as in aquifuge or impermeable terrains).
Impermeable formations serve as boundaries to aquifers;
2. (noun) An impermeable body of rock,
with no interconnected openings
and thus lacking the ability to absorb and transmit water.
area of pumping depression Syn: contributing region
Ð Area within the zone of influence where all flow lines are directed towards
the well being pumped. Note: do not confuse with radius of influence.
The standing water-level remains virtual as long as a borehole or a piezometer
has not attained the aquifer, lying always above the base of the overlying
impermeable layer. The artesian condition is said to occur when the standing
level remains higher than ground level after a borehole has pierced the base
of the containing bed (c.f. gushing artesian well).
Ð Groundwater present in a confined aquifer, which flows into wells without
pumping or gushes out onto the ground surface; the piezometric level is
situated above the ground surface.
artesian well Syn: overflowing well
Ð A well that gushes or flows out onto the surface without pumping.
Ð Planned operation of transferring water from the ground surface into aquifers.
The quantity, quality, location and timing of artificial recharge are decision variables,
the values of which are determined as part of the management policy of a
given groundwater system.
Ð Near-field sanitary protection zone surrounding a water well.
Ð Series of different behaviours observed with increasing water content of a
soil. Bentonites are characterized by their Atterberg limits, (e.g. liquid
limit, plastic limit, plasticity index).
Ð Chemical attack of metals brought about by the proliferation of microorganisms
in water wells.
This phenomenon is due to the presence of bacteria in groundwaters,
(cf. biological corrosion).
Ð Rapid development of bacteria under favourable microenvironmental
conditions. Associated with zones of increased nutrient flux into the well,
Ð Chemical substance capable of destroying bacteria or restricting their
During drilling, the hole is cleaned progressively by the lowering of a bailer
which allows the cuttings to be brought to the surface .
barite Symbol: BaSO 4
Ð Barium sulphate. Barite is used for weighting up the drilling fluid , (also
known as barytes).
Ð Chemical reaction whereby a cationic species in solution replaces another
from the solid phase. Secondary phenomena which can bring about modifications
in the chemical composition of the groundwater during its residence time in
Ð A method for cutting a water well in which the casing penetrates under its
own weight or is rammed by hydraulic jacks. Drilling by cutting is better
known as the Benoto process .
bentonite mud , bentonitic mud
Ð Drilling fluid based on natural smectite-rich clay. This type of mud cannot
be used in water-wells; it has the characteristic property of reacting and
flocculating in the presence of nitrate-rich water.
Berkaloff has combined the Hantush and Boulton approaches to give practical
rules of interpretation for pumping tests , (cf. pumping test analysis).
Ð A relation describing the conservation of energy in the laminar flow of an
ideal fluid, stating that: p/d + gz + (v²/2) is constant along any stream
line, where p is the fluid pressure, d is the fluid density, v is the
velocity, g is the acceletion due to gravity and h is the height of the
pressure head. To obtain the discharge rate of the pumped water passing
through the plate orifice of a Pitot tube of diameter D, the equation can be rewritten:
Q = C d² /
h, where Q = discharge rate, C = coefficient of the experimental flow rate
depending on d/D,
d = diameter of orifice and h = height of the pressure head.
Includes activity due to I-131, Cs-137 and Sr-90, but tritium is excluded
the definition of overall beta-emitter radioactivity given by the ICRP,
(c.f. radionuclide, alpha-emitter radioactivity).
Ð Accumulation of gelatinous or viscous material due to bacterial activity in
or around a water well.
Ð The deterioration of metals as a result of metabolic activity of
microorganisms, (cf. bacterial corrosion)
Ð Mass of living organisms per unit surface or unit volume in a given
environment, (cf. bacterial proliferation).
Ð Procedure used for the analysis of pumping tests in unconfined aquifers, in
which delayed yield is taken into account. Boulton has tabulated the limited
recharges which, for example, can be produced by a secondary aquifer; after an
initial yield from the aquifer due to pressure release, water is gradually
released from unsaturated zone storage by gravity drainage , (cf. pumping test
Ð Frequently used type of well screen with raised ribs; it is constructed
flat, then rolled and welded. Possesses good mechanical resistance and shows
an open area varying between 3 and 27% according to the dimensions of the
perforations, (cf. screen).
The main drawback in using bentonite mud is that it clogs the water inflow
sections with an excessively thick cake, once drilling is complete, the cake
forms a more or less waterproof crust on the well walls.
cementation , cementing
Ð The operation whereby cement slurry is pumped into a drill hole and forced
in behind the casing for such purposes as sealing the casing to the walls of
the hole, preventing unwanted leakage of fluids into the hole or migration of
fluids from the hole, closing the hole back to a shallower depth, plugging an
abandoned well, etc.
Before undertaking cementation, the exact volume of the cement slurry to be
used must be calculated, then the quantity of cement slurry required to fill
the annular space is introduced at the bottom of the well .
Ð Cylindrical, cage-like device fitted to a well's casing as it is run to keep
the pipe centered in the borehole. Cementing centralizers are made with two
bands that fit the pipe tightly with spring steel ribs that arch out to press
against the wall of the borehole. By keeping the pipe centered, a more uniform
cementing job is assured; centralizers are especially used in deep or deviated
characteristic grain diameter
The characterisitc grain diameter of a material is defined so that, in
relation to the total weight of the sample, 10% of the grains are finer and
90% coarser than this dimension; it represents the x-axis coordinate of the
90-percentile grain-size class , (also known as characteristic diameter).
chelating power Syn: complexing efficiency
Ð The ability of certain bodies to complex cations to form a so-called ring
Ð Chemical weathering of rocks or well casings by hydration, hydrolysis and oxidation.
Ð Reduction in the porosity of the gravel pack due to processes of
precipitation caused by increased oxygenation, (e.g. carbonate clogging, iron-
Ð Attack of metals not involving electrochemical processes. In the context of
water wells, better termed non-electrochemical corrosion. This type of
corrosion corresponds to reactions governed by the fundamental laws of
kinetics which occur without being accompanied by an electric current. Note:
avoid the term chemical corrosion; non-electrochemical corrosion is correct
Ð Declogging procedure involving the use of a chemical treatment. The chemical
reagents used comprise acids and polyphosphate, (e.g. acidification,
Ð Any procedure for well development making use of chemical methods to loosen
and remove material clogging the catchment structure.
Ð In general, a binary compound containing chlorine combined with another
element or radical.
The dissolved chlorides in water may be derived, among other sources, from
salt formations in potassic evaporite basins. Since chlorides are not absorbed
in the soil, they can be transported over long distances . In addition, they
may originate from excessive pumping near the sea coast.
Ð Quantity of active chlorine present in a unit volume of reagent, expressed
in degrees, where 1 = 3.17 g active chlorine per litre.
Ð The act of bringing the phenomenon of detergency into effect (detersion and
cleaning are terms standardized by ISO).
Ð Pumping carried out to remove material brought into well during development.
coefficient of permeability Syn: specific permeability
Ð The volume of mobile water in m 3 transmitted perpendicularly to the flow
direction in unit time (s) through a unit cross-section in m², under the
effect of a unit hydraulic gradient and within the conditions of validity of
Darcy's law. Note: the Meinzer unit is defined as the rate of water flow in
gallons per day through a cross section of 1 square foot under a unit
hydraulic gradient, at the prevailing temperature or at 60 F (16 C).
Also known as the permeability coefficient, Meinzer's coefficient of
permeability (cf. hydraulic conductivity).
Ð A suspension of very small particles (a few microns in size) of various
insoluble substances in a liquid medium. Flocculation is prevented by the high
surface tension and viscosity of water as well as the electric charge on the
surface of the particles. Changes in the pH of the medium or the concentration
of salts will bring about flocculation and precipitation of the solid phase,
(cf. biological clogging).
Ð Gelatinous or viscous masses of flocculate associated with the biological
clogging of water wells, (cf. gel).
complexing efficiency Syn: chelating power.
compressed-air treatment (cf. physical treatment).
Ð The current transferred across unit area per unit potential gradient. The
conductivity of water is a relatively reliable indicator of its
mineralization . Knowing the hydraulic conductivity of a reservoir, it is
possible to calculate the discharge rate of an aquifer; conductivity increases
with the concentration of dissolved salts and varies as a function of
temperature. It is expressed in microsiemens/cm, and is the reciprocal of
cone of depression , cone of influence, groundwater hole
Ð Concave downward depression in the piezometric (potentiometric) surface of a
groundwater body, defining the area of influence of a well.
confined aquifer , artesian aquifer, pressure aquifer
Ð Aquifer bounded above and below by impermeable beds, or by beds of
distinctly lower permeability than in the aquifer itself (e.g. Bunter
Sandstone, Lorraine; Albian sands, Paris Basin). The water-bearing formation
is saturated throughout its thickness and is capped by a permeable or semi-
permeable layer, (c.f. aquifer, unconfined aquifer, leaky aquifer).
confining pressure Syn: geostatic pressure
Ð Sum of hydrostatic and lithostatic pressures, or total pressure exerted on a
system. An isotropic pressure resulting from the load of overlying rocks, or
hydrostatic pressure resulting from the weight of the water column in a zone
of saturation, (cf. lithostatic pressure).
Ð A measure of the degree to which a climate is affected by continental
influences (or remoteness from maritime influences).
Ð Method of well development in which the well is pumped at the physical yield
limit for a short period in order to induce surging. The rapid alternation of
pumping and non-pumping is known as rawhiding, (c.f. alternating pumping,
convection time (c.f. transfer time, residence time).
Ð Complex set of electrochemical or purely chemical phenomena involving attack
of metal casings and screens, the accumulation of carbonate and iron-manganese
precipitates, and even bacterial activity; e.g. uniform corrosion, pitted
corrosion, cracking corrosion, (c.f. electrolytic corrosion, bacterial
critical discharge Symbol: Qc
Ð Well discharge corresponding to the velocity threshold between laminar and
turbulent flow regimes. In practice, the pumping discharge should always be
lower than the critical discharge , (cf. critical velocity).
Ð Corresponds to the velocity at which critical discharge occurs, (cf. Reynold's number).
cutting Syn: holing.
In this type of drilling by sand washing or cutting, the casings penetrate
formation through the effect of their own weight or the action of a hydraulic jack,
(cf. Benoto process).
Ð States that the rate of movement of water through porous media is
proportional to the hydraulic gradient; it can be expressed as u=Ki, where u
is the volume of water transmitted through a unit cross-sectional area per
unit time, K is the hydraulic conductivity and i is the unit change in head
through unit length of flow path. The circulation of groundwaters is governed
by Darcy's law , (c.f. hydraulic gradient, discharge).
Ð Removal of encrustations, colloidal deposits or organic material from
various parts of the catchment structure.
Ð Dispersion of colloidal deposits or mud cake to form a suspension, (cf.
degrees Baumé Abbr: Bé
Ð Divisions of a scale for measuring the specific gravity of liquids, still
used in French-speaking countries to express the concentrations of solutions
with densities greater than water. Slightly different from the A.P.I. or
Twaddell scale: modulus A.P.I. gravity = [141.5/specific gravity] - 131.5;
modulus degree Bé = [140/specific gravity] - 130 i.e. 0 Bé is equivalent to a
specific gravity of 1.0 at 15 C, and each division on the scale represents a
specific gravity increment of 0.004.
delayed storage coefficient
Ð The volume of water released from unsaturated zone storage (under gravity
drainage) per unit surface area of aquifer per unit change in head.
Ð Reduction of nitrate, due to bacterial activity, to form nitrite and then
elemental nitrogen, usually in an anaerobic environment.
density (of drilling fluid)
The density of pure water (at 4 C) is unity. The density of fluid mud can vary
between 0.8 and 2, and is measured with a Roberval balance, or
preferably a Baroid balance.
Ð A measure of water flow at a particular point; in the case of a water well,
the discharge rate is usually given in cubic metres per day.
Ð Process in which a substance looses its cohesiveness, due to the hydrating
power of water, leading to a partial or complete breaking of the various
electrostatic bonds between the atoms and the molecules of the substance
entering solution. Dissolution is said to occur when solvation is complete,
distribution system , mains water supply.
domestic (or drinking) water supply well Abbr: DWS well
Ð Catchment structure providing water for household consumer use, not intended
for irrigation or industrial uses.
down-the-hole hammer drilling Abbr: DTH drilling
Ð A drilling method utilizing impact accompanied by thrust from the tool,
which is itself rotating. A pneumatic hammer fitted with drill bits is
attached to the end of the drill string. The percussive action is driven by
releasing compressed air into the drill string. This process is of great interest
in hydrogeological work, mainly in hard terrains.
A number of rapidly-setting cements available on the market can
be used to limit the downtime of drilling operations.
Ð Hydrological system bordered by watersheds which delimit the catchment area
of a watercourse and its tributaries. The only input of water into a drainage
basin, which is assumed to be closed, comes from effective precipitation. Also
termed drainage area, catchment, catchment area, catchment basin, gathering
ground, feeding ground or hydrographic basin (cf. hydrological system).
Ð Characterizes the slow downward percolation of waters from the unsaturated
zone into an unconfined aquifer; do not confuse with leakage factor.
drawdown Syn: depletion
Ð Lowering or depression of water-table caused in most cases by pumping.
Corresponds to the difference between dynamic level and standing water-level
for a particular well.
One or more very heavy drill collars may be placed above the drill bit to
increase the vertical pressure on the tool, in order to facilitate the
penetration and ensure straightness of the hole.
driller's log Syn: instantaneous log
Ð Record of daily drilling with description of formations encountered, also
containing information on casings, screens and water level in well.
Ð A suspension of finely divided heavy material, such as bentonite and barite,
pumped through the drill pipe during rotary drilling. The rotary drill
requires the use of a drilling fluid prepared on site which is injected
continuously and under pressure into the hollow drill pipes of the string. The
drilling fluid may be composed of clear water, bentonite mud or mud with a
synthetic biodegradable polymer base; it has several functions: cooling and
lubricating, flushing out of chippings from the geological formations,
consolidation of the borehole with cake, protection against water inflow and
providing useful information on loss of head . The density is adjusted by
weighting up (barite) or lightening (water), while viscosity is adjusted by
thinners or viscosifiers. Can also be called drilling mud, drill fluid, drill
mud, mud fluid, mud flush, circulating fluid, circulation fluid, circulation
medium, driller's mud, mud water, flushing mud, rotary mud (cf. bentonite
drilling log sheet , well data sheet.
drilling rate Syn: rate of penetration (abbr: ROP)
Ð A measure of the speed with which the bit drills into formations; usually
expressed in terms of feet per hour. The rate of penetration in soft terrains
is high and can reach 100-150 m a day.
drill pipe string , string of rods, drilling string
Ð Lengths of pipe, casing or other downhole drilling equipment coupled
together and lowered into a borehole. The whole assembly is made up of the
following elements, from top to bottom: a swivel, a square drill pipe,
ordinary drill pipes, drill collars and a tool. The drill pipes are hollow so
that mud can be injected into the bottom of the borehole.
drill reamer , reamer, drilling reamer, reaming shell, core shell, reamer shell
Ð A short tubular piece designed to couple a bit to a core barrel. The outside
surface of the reaming shell is provided with inset diamonds or other cutting
media set to a diameter to cut a specific clearance for the core barrel
drinking water supply Syn: ?domestic water supply (abbr: DWS)
Ð Distribution network supplying water that is fit for human consumption.
dynamic level Syn: pumping water-level
Ð Height of groundwater level when disturbed by pumping.
Ð Special type of electrical potential method, in which one of the current
input electrodes is placed at a point on the conductor while the other
electrode is placed at infinity. In this context, earthing may be employed as
a strategy in support of prospection. Since the conductor is everywhere at
roughly the same potential, the ore body or underground river is delimited by
Ð1: The volume of mobile water, Ve, that a saturated reservoir can contain and
subsequently release when fully drained, divided by the total volume of the
reservoir, Vt; i.e.: ne = Ve/Vt. Since a reservoir is never completely drained
of its water content, effective porosity is more commonly used in hydrogeology
than the more theoretical concept of absolute porosity;
Ð2: the property of a soil or rock containing interconnecting interstices
expressed as a percentage of the bulk volume occupied by these spaces,
(cf. void space volume).
Ð Amount of water from precipitation that remains available at the ground
surface after subtraction of losses due to true evapotranspiration. Fraction
of precipitation that can infiltrate into the soil or contribute to run off,
(cf. run off, evapotranspiration).
effective transfer capacity , effective velocity, average interstitial velocity
Ð Carrying capacity of waters infiltrating through a medium, (cf. purifying
electrical water-level gauge , tape.
electric log , electrical log
Ð Geophysical survey technique based on resistivity or self-potential;
provides information on the thickness and nature of water-bearing formations
with a view to groundwater extraction. An electric log typically consists of
the spontaneous-potential (SP) curve and one or more resistivity or induction
curves. The Archie equations form the basis for the interpretation of electric
logs, (cf. geophysical log).
electric panel array
Ð Survey method consisting of measuring apparent resistivity between two
electrodes, for different positions of a third electrode. Panel-type arrays
are commonly employed to reveal or confirm the presence of major structural
features, in which case the array is operated at right angles to the inferred
structural trace . Such surveys enable the emplacement of exploratory boreholes
near faults, in order to confirm their role as drains or impervious
Ð Electrical prospection based on the conductivity of subsurface formations,
or their capacity to conduct an electric current, whether natural or
artificial; they do not involve measuring the magnetic field. Electric survey
methods make use of: natural (telluric) currents: spontaneous (or self)
polarization and artificial currents: electrical potential (mapping of
potential difference, with earthing, etc), resistivity method (electric
logging, resistivity rectangles).
electric water-level gauge
Tapes with electric contact gauges are satisfactory for measuring the
piezometric level. A good quality probe enables measurements to the nearest
centimetre for absolute values of 30-50 m, (also termed electric water-level
Ð Form of chemical attack on metals involving galvanic couples or gas
electrode processes, (e.g. hydrogen corrosion, oxygen corrosion).
electrochemical series , electromotive series
Ð List of half-cell reactions arranged in order of decreasing equilibrium
potential with respect to the standard hydrogen electrode; also reflects
increasing susceptibilty of metals to electrolytic corrosion, (cf. standard
Ð Phenomenon controlling the self-potential measured during an electric log
survey, resulting from the migration of waters towards the middle of a porous
electrolytic cell Syn: galvanic couple
Ð An electrode system in which a potential is set up between two metals having
different tendencies to go into solution; e.g.: Zn + Cu ++ = Cu + Zn ++,
(cf. electrochemical series).
electrolytic corrosion (cf. electrochemical corrosion).
electronic data logger , automatic data aquisition system
Ð Apparatus allowing the acquistion of large quantities of data from
device in real time. Used to store very precise and closely spaced measurements
of parameters such as water level, pressure, temperature, conductivity
cf. analogue recorder
electroosmosis , electro-osmosis
Ð Electromotive force proportional to the logarithm of the restivitity ratio
between two different electrolytes. It is an important parameter contolling
self-potential in an electric log survey, caused by the transport of water
from one electrode to another, (also known as electroendosmosis in the
Ð Carrying off of solid particles into a flowing medium.
Ð Flow rate at which groundwaters pass through the well screen openings, (cf.
uniform inflow distribution).
equilibrium pH Symbol: pHS
Ð Precise value of pH beneath which waters become aggressive and above which
the waters are encrusting.
Second term in Jacob's equation - equivalent to the well function under a
quasi-steady state regime - that tends towards a constant value when
the radius of influence is infinity.
Ð Process whereby water is lost by the soil to the atmosphere though the
action of evaporation from wet surfaces combined with transpiration, the
exhalation of water vapour by plants, largely from their leaves. Evaporation
takes place from the surface of free bodies of water (oceans, seas, lakes and
rivers) as well as from vegetation. Both of these phenomena - evaporation and
transpiration - are brought together under the term evapotranspiration.
extractable storage Syn: mineable storage
Ð The maximum volume of water that can be economically extracted from the
total storage of an aquifer, (cf. reserve).
Ð Scale or colloidal deposits formed from the accumulation of insoluble iron
hydroxides, usually due to oxygen corrosion or bacterial activity in the zone
of temporary saturation, (cf. iron-manganese hydroxides)
fictitious radius Symbol: Rf
Ð The distance at which the drawdown, as calculated by the Jacob expression,
falls to zero. It is a function of the transmissivity and the storage
coefficient, (also known as the critical radius, "imaginary" radius).
Ð Solid matter load present in a drilling mud sample, evaluated by measuring
filtrate volume on a Baroid balance, (c.f. mud filtrate, filtrate volume).
If the filtrate volume is excessive with respect to a given volume of drilling
mud, then the cake is too thin and the walls are not held firm leading to a
real risk of collapse. If the filtrate volume is too weak there is a risk of
the mud clogging the water-bearing formation , (cf. filtrate strength).
fishing, fish job, grappling
Ð Searching or attempting to recover a piece of equipment fallen into a well
float shoe method
Ð Cementation method using a special device which is placed at the lowermost
end of the casing string. The float shoe consists of a plastic ball which acts
as a plug preventing the passage of fluids from the bottom upwards. It is also
in contact with the surface by means of a pipe screwed to the cementation
shoe, thus allowing the cement slurry to pass into the annular space.
Ð Aggregation of clay minerals and other fine particles to form flocs.
Influx from gypsiferous terrains can lead to flocculation .
floccule Abbr: floc
Ð A loose fluffy or foamy mass formed by the aggregation of fine suspended
flow meter, micro-current meter
Ð An instrument used to measure velocity of currents flowing in a water well,
(fluid meter, flow indicator, flow-measuring device).
Ð A graphical representation of flow lines and equipotential (piezometric)
lines used in the study of seepage phenomena, (also known as hydraulic flow
Ð The respective and simultaneous effects of several different causes of
change in groundwater level at a given point. In porous media, these different
water flows can be added together algebraically.
Ð Said of materials suitable for use in food packaging or drinking water
Ð Ability to transmit water due to the presence of fracture porosity. Within
limestone massifs, the fractures are commonly open, thus providing channels
which allow the very rapid circulation of groundwaters; a non-porous rock can
behave as a reservoir if sufficiently fractured, (cf. karst aquifer).
Ð Development technique making it possible to widen existing fractures or
create new ones in order to improve the specific capacity of a well. There are
two types of artificial fracturing: hydraulic fracturing (or hydrofracturing)
and fracturing by explosives.
free plug method
Ð A destructible cementation plug is introduced into the casing string to be
sealed before or after injection of the cement slurry.
Ð Downhole profile of induced radioactivity showing the bulk density of rocks
and their contained fluids. A porosity log of the wall-contact type indicating
formation density by recording the backscatter of gamma rays, (also known as
density log, scattered gamma-ray log, densilog).
gas electrode process
Ð Half-cell reaction involving a gaseous species (e.g.: Pt, H 2/H +).
Ð Gaseous compounds held in solution in water (e.g. oxygen, carbon dioxide,
methane, hydrogen sulphide). The concentration of dissolved gases is governed
by Henry's law, and is an important indication of water quality, (cf. Henry's
Ð Gelatinous material formed from the coagulation of a colloid, (cf. colloidal
Ð Downhole recording of properties in a well or in adjacent geological
formations (e.g. self-potential, resistivity, gamma ray, gamma-gamma,
neutron). The three main categories are: formation, structural and fluid logs,
(cf. electric log).
A grab bucket is used to empty progressively the inside of the casing as long
as it is situated above the standing water-level .
The choice of the gravel used in the pack is based on granulometric analyses
of the aquifer formations that are to be tapped. These analyses make it
possible to define certain parameters such as the characteristic diameter, the
fineness index or the sorting coefficient.
Ð A mass of very fine gravel that is placed around a well screen. Gravel
packing is a method of well completion in which a slotted or perforated liner
is placed in the well and surrounded by a very fine-mesh gravel. Different
methods such as gravel packs, sand consolidation and well screens are used to
control the influx of sand.
Ð Geophysical survey technique based on the force of attraction between
masses, giving rise to an acceleration g - due to gravity - which affects all
bodies placed near the surface of the globe.
groundwater Syn: underground water
Ð Subsurface waters contained in aquifers beneath the soil-water (or
Ð That part of a drainage basin situated beneath the ground surface.
A groundwater basin can be made up of one or more aquifers, whose boundaries
are constrained by geological structures; its recharge takes place through the
infiltration of effective precipitation , (cf. hydrological system).
groundwater body , water-sheet
Ð Mass of subsurface water contained within permeable geological formations,
Ð The upper surface of groundwater, or the level below which an unconfined
aquifer is permenently saturated with water, (also known as water-table,
groundwater level contour
Ð Line of equal piezometric level (also: line of equal hydraulic head,
hydraulic head contour, groundwater contour, groundwater table contour).
gushing artesian water Syn: overflowing artesian water.
Ð An electrode process forming part of a galvanic couple, in which a potential
is set up between a given metal species and the electrolyte, e.g.: Zn - 2e =
Zn ++ (at the anode), Cu + 2e = Cu (at the cathode).
Ð Technique for analysing pumping tests in a non-steady state regime, in which
a semi-log relationship between drawdown and time is established for a given
observation well. Hantush has tabulated the high recharges which bring about
permanent stabilization of the observation wells after the initial drawdown ,
(cf. pumping test analysis).
Ð The amount of a gas dissolved by a given amount of liquid at a given
temperature is proportional to the temperature, the volume dissolved being
independent of pressure.
One of the two main types of groundwater reservoir, showing fracture
permeability and generally composed of limestones but also volcanic,
metamorphic and granitic rocks, (cf. homogeneous aquifer).
If the wall cake does not detach itself, hexametaphosphate is used to clear
out the hole .
Ð Records of technical information acquired during testing, operation and
development of a well.
Ð One of the two main types of groundwater reservoir, showing pore-space
permeability and made up of sands, gravels and sandstones. Homogeneous
aquifers are associated with alluvial deposits occupying valley floors and
account for part of the groundwaters of major sedimentary basins; the
groundwater discharge rates are generally low , (cf. heterogeneous aquifer).
Ð Chemical combination of water with another substance. The weathering of
rocks and minerals involves penetration of water into the lattice of
crystalline solids; do not confuse with hydrolysis.
Ð A measure of permeability with dimensions of length per unit time, denoted
as K in Darcy's law. It corresponds to the coefficient of permeability only
when the fluid is water at moderate temperatures; hydraulic conductivity has
the dimensions of velocity and is expressed in m/s. Also known as coefficient
of hydraulic conductivity or hydric conductivity, (cf. Darcy's law, coefficient of permeability).
Ð Change in head through unit length of flow path; the h/l ratio is denoted as
i in Darcy's law, where h is the head (height of the water column) in metres,
proportional to the weight of the water column and l is the height of the
cylinder in metres, (cf. Darcy's law).
hydraulic head Syn: total head
Ð The difference in piezometric level between the recharge and discharge areas
of a hydrological system, calculated as the sum of elevation potential energy
possessed by a given mass of water, its pressure head and velocity head. Also
termed potentiometric head, total static head. Note: not to be confused with
pressure head, (cf. static head).
Ð Device used to facilitate the lowering or extraction of casings in a water
hydrochloric acid Symbol: HCl
Ð A solution of hydrogen chloride gas in water. A poisonous, pungent liquid
forming a constant-boiling mixture at 20% concentration in water, widely used
as a reagent, (muriatic acid and spirit of salt are obsolete synonyms).
Chemical attack of metals in unaerated media, incorrectly termed chemical corrosion.
hydrogen potential Symbol: pH, (cf. pH).
hydrogen sulphide , hydrogen sulfide; symbol: H 2S
Ð Gaseous compound giving rise to aggressive and corrosive properties when
dissolved in water. Waters containing H 2S will attack steel and form iron
sulphide encrustations. It is characterized by a smell of rotten eggs, (also
known as hydrosulphuric acid, sulphuretted hydrogen).
Ð Study of the chemistry, physics and environmental aspects of water at the
Earth's surface, including the mechanisms of storage and flow in groundwaters.
Also used in the more restricted sense of "ground-water geology" only
hydrographic basin , catchment area, drainage area, drainage basin
Ð A region or area bounded by a drainage divide and occupied by a drainage
system. Otherwise termed a catchment basin, gathering ground, feeding ground,
(cf. river basin).
hydrological cycle Syn: water cycle
Ð Natural cycle in which water evaporating at the Earth's surface - mostly
from the oceans - passes into the atmosphere and falls back as precipitation.
Ð Dynamic system which corresponds to a resource - variable in space and time
- forming part of the global water cycle, (e.g. drainage basin, groundwater
Ð Decomposition of mineral salts brought about by the action of water, owing
to the dissociation into H + and 0H- ions which leads to exchange reactions
with crystalline solids. Plays an important role in the destructive action of
water on silicates and the formation of hydroxyl-bearing minerals such as
micas and chlorite. Also known as hydrolytic alteration or hydrolytic
decomposition, (cf. hydration).
Ð Pressure exerted by the overlying water, (cf. confining pressure).
Ð A structural trap forming a lateral boundary to a groundwater body.
Ð The natural or artificial introduction (recharge) of water into the ground.
Infiltration involves flow into a substance, in contradistinction to
percolation, which implies passage through a porous substance (e.g. a bed of
solid absorbant). In general, the process consists of the slow laminar
movement of water through the pore spaces of soil and rock, while flow in
large openings such as caves is not included.
infiltration basin Syn: seepage basin
Ð Engineered structure used for the artificial recharge of an aquifer.
Ð Flow rate of water infiltrating through a medium. The infiltration capacity
is evaluated by cumulating the rates over a period of time.
Calcic bentonite can be transformed into sodic bentonite by the addtion of
sodium carbonate; the swelling of these bentonites can vary between
10 and 15 times.
Ð Microorganisms capable of metabolizing iron present as minerals or organic
complexes (e.g. Gallionella, Toxothrix). Siderophile bacteria are present in
most aquifers and use iron as a source of energy; some iron bacteria are
chemicolithotrophic (e.g. sulphate-reducing bacteria, siderocapsaceans) and do
not use ferrous iron at all, while others metabolize manganese instead (e.g.
Metallogenium ), (cf. sulphate-reducing bacteria).
Ð Precipitation of iron and manganese compounds, forming encrustations on
various parts of the well structure.
Ð Compounds generally responsible for iron-manganese clogging, formed in the
zone of temporary saturation if the screen is dewatered, (cf. ferruginous
Ð Method for the evaluation of pumping test data under constant-discharge
conditions, (cf. pumping test analysis).
Ð Method in which a tool with pressurized water jets is rotated as it is moved
past the section of the screen to be treated. The fine particles penetrate
into the screen where they are recovered by pumping or with a bailer; the
efficiency of this procedure depends on the type of screen, being optimal for
screens of the Johnson type, (also known as high-pressure jetting).
jet cleaning head Syn: jetting head
Ð Downhole tool fixed to the drill stem of a rotary rig, used for high-
pressure jetting of the screen face.
Ð Screen with a continuous horizontal opening running the whole length of the
screen. The main advantages of such a screen are: the regularity and precision
of the opening, the very low risk of clogging and the highest open area
coefficient of all the screen types, (cf. screen).
Ð Type of topography developed in limestone terrains, formed as a result of
variable degrees of dissolution by meteoric waters, (cf. karst aquifer).
Ð Water-bearing formation where most of the storage is in solution channels
and fracture porosity, (cf. fracture permeability, karst).
Incorporates all nitrogen present in organic or ammoniacal form; it should
be confused with total nitrogen which also includes nitrates and nitrites.
Ð Fluid flow characterized by the gliding of fluid layers (laminae) past one
another in an orderly fashion. As a preliminary hypothesis, it is necessary to
assume that groundwaters exhibit laminar flow over most of their transport
path, (cf. Reynolds number).
Ð Recent satellite in a series carrying multispectral scanners and thematic
mappers, which provides a better resolution at ground level (30, 20 or 10 m).
As a result, such images can reveal just as must detail as aerial photographs
at a scale of 1:50,000, (cf. remote sensing).
Ð The value obtained by subtracting the saturation pH (pHs) from the measured
pH of a water sample. The Langelier index can be used to determine whether a
water is scale-forming or aggressive.
leakage Syn: interformational flow
Ð Draining or passage of fluids from one formation to another.
leakage coefficient Syn: leakance factor
Ð Parameter with the dimensions of reciprocal time, equivalent to the
hydraulic conductivity divided by the thickness of the semi-pervious
interlayer. It is a measure of the capacity of a leaky interlayer to transmit
Ð Parameter with the dimensions of length used to characterize the effects of
leakage in a semi-confined aquifer. Not to be confused with leakage
leaky aquifer Syn: semi-confined aquifer
Ð Aquifer overlain and/or underlain by a relatively thin semi-pervious layer,
through which flow into or out of the aquifer can take place. The confining
bed and/or substratum of an aquifer is often made up of a semi-permeable
hydrological formation. Under certain favourable hydrological conditions
(difference of pressure head), the semi-permeable layer allows the exchange
of water with the overlying or the underlying aquifer. This phenomenon,
which is known as leakage, implies the presence of an aquifer containing
semi-confined groundwaters. (c.f. aquifer, confined aquifer, unconfined
Lightening of a drilling mud is achieved by adding water .
linear loss of head Symbol: BQ
Ð Reduction of hydraulic head generated by laminar flow of water into the
aquifer close to the well. It is constrained by the hydrodynamic parameters of
the aquifer and increases with the duration of pumping, (also known as linear
well loss, linear head loss).
lithostatic pressure Syn: lithostatic load
Ð Pressure exerted by overlying ground or strata, (cf. confining pressure).
Ð Screen with horizontal rectangular perforations in the form of a hood.
Mechanically resistant but with a low open area, (cf. screen).
Ð Type of absorption test providing a value for hydraulic conductivity at a
given point in the well. The hydraulic conductivity so obtained arises from
fracture porosity; 1 Lugeon permeability unit corresponds to the absorption of
1 litre water per metre depth in the well per minute at a pressure of 1 MPa,
(cf. absorption test).
Ð An instrument for measuring pressure, but which can be adapted to measure
Ð A waterproof piezometric pipe which goes down into the well and which is
fixed along the pump column.
maximum acceptable drawdown
Ð Criterion determined by physical and technical constraints of the aquifer
complex/catchment structure, expressed by the critical discharge, Qc, and the
corresponding critical drawdown, Sc, as measured from well tests.
Ð Movement of fine particulate matter into the near-field well environment and
gravel pack, leading to aquifer losses. Particularly important in overpumped
wells, (cf. aquifer development).
mechanical declogging Syn: swabing
Ð Physical method of development based on surging water backwards and forwards
by means of a plunger. Used to clean screens, gravel pack and aquifer matrix.
mechanical weathering , disintegration, crumbling
Ð Disaggregation of rock masses under the effect of weathering, leading to the
release of debris of various different grain sizes.
Ð Fluid remaining after deposition of mud cake. If the drilling fluid is too
thin, filtrate may be driven into the surrounding permeable formations.
Measurements are taken with a Baroid press, in which is placed a sample of the
mud to be strained, (cf. filtrate strength).
Ð Leakage of drilling fluid through well walls into the surrounding terrain. A
fairly frequently encountered situation arises from total loss of mud which
places the well structure in real danger .
Ð Organic products derived from Guar gum, used to enhance viscosity during
drilling operations (e.g. Revert, Foragum). For the same amount of matter with
the same viscosity, their molecular structure enables them to produce ten
times more gel than a bentonitic mud.
90-percentile class Syn: 0.9 quantile
The sorting coefficient is expressed as the quotient of the diameters of the
40- and 90-percentile classes on the cumulative grain-size curve.
non-steady state regime
Ð Regime which takes account of the observed fact that the size of the cone of
depression increases as a function of pumping time. Also termed non-
equilibrium regime, (cf. steady-state regime).
Ð Inflow of dissolved minerals essential for bacterial proliferation.
Increased nutient flux is often linked to high entrance velocities across the
observation well Syn: piezometer
Ð A generally narrow well or tube designed to measure the water-table level or
hydraulic head at a particular point. In theory, observation wells are set out
along two rectangular axes centred on the control well and at incresing
distances away from it, the distance of the last one being close to the
estimated radius of influence; observation wells must have a very low response
open area coefficient Syn: open area
Ð Open area coefficient: C = f / f + 1 where f is the dimension of the slot
between two coils and l is the width of the encasing wire. Fundamental
parameter controlling the inflow of water from the aquifer towards the well.
operation (of water wells)
Ð The techniques or actions used for extracting groundwaters from aquifers.
Planning the extraction of groundwaters depends on the evaluation of water
reserves and resources. More generally, the extraction of mineral resources or
Earth materials from the surface or subsurface, (the term abstraction is used
for groundwaters, and mining for mineral ores).
Ð Dissolved organic matter present in water (e.g. polyaromatic hydrocarbons,
phenols, carbon tetrachloride, pesticides).
Muds with emulsified oil are obtained by adding diesel fuel and an organic
emulsifier to standard mud.
orthophosphoric acid Symbol: H3PO4
Ð Water-soluble, transparent crystals, melting at 42 C; phosphoric acid is
obtained cormmercially from phosphate rock.
overextraction , overdevelopment, groundwater overdraft
Ð Abtraction of groundwaters at a rate above the safe or sustainable yield,
not to be confused with overpumping.
Ð Simplest method of well development, which consists of pumping at a rate far
above the estimated water extraction capacity. There are risks of irregular
development as a result of vertical variations in the permeability of the
terrain. This type of development can provoke a compaction of the fine
sediments, which causes a reduction in permeability, while sand bridging
formed by unidirectional flow may also lead to a lowering of yield, (cf.
This reaction particularly concerns oxides that are deficient in oxygen, as
well as sulphides such as pyrites and also organic matter. It is a phenomenon
of considerable importance in highly oxygenated infiltration zones, but its
effect is also felt to a lesser degree at greater depth
Ð Chemical attack of ferrous metals in aerated waters, due to to a gas
electrode process involving oxygen. Characterized by the formation of ferric
hydroxide blisters which accumulate around the anode.
It is possible to cement only a part of the cased section by carefully
estimating the volume of cement to be employed. In this way, the lower or
upper part of catchment structure can be cemented, this procedure is
particularly useful for separating water-bearing horizons superimposed one
above the other
Ð A process involving the elevation of temperature for an appropriate period
of time, for the purpose of either inactivating microorganisms, particularly
pathogens, or decreasing their number to a specified level.
peptization power Syn: dispersive capacity.
Ð Method that consists of raising a heavy tool (churn drill bit) and letting
it fall onto the terrain to be traversed, the height and frequency of the drop
being varied according to the hardness of the formation. Also known as
percussion boring, percussion system or percussive drilling.
Ð Fraction of the total reserve that is not replenished. In the case of
unconfined groundwater, its upper surface corresponds to the mean mininum
water table. For confined bodies, the permanent storage is very similar to the
total groundwater storage, (cf. reserve).
permeability Syn: perviousness.
e.g. simazine, atrazine.
Ð The negative logarithm of hydrogen ion concentration, a measure of the
acidity or the basicity of a solution ranging on a scale from 0 (acidic) to 7
(neutral) to 14 (basic). pH measurements are of considerable interest since
they reveal contamination by cement or by water from the aquifer, and also
indicate the risks of flocculation of the drilling mud , (cf. hydrogen potential)
A rapid and cheap method for drawing up a structural or geological sketch
thus representing a valuable adjunct to geological and soil surveys which provide
the essential information for choosing the location of a borehole.
Photographic interpretation may be applied to conventional aerial photogrammetry
and satellite imagery, (cf. remote sensing).
Ð Pneumatic or hydraulic technique of well development/restoration used to
break up mechanical clogging in the gravel pack, (e.g. controlled overpumping,
air-lift pumping, compressed-air treatment).
Ð A generally narrow observation well or tube designed to measure the
water-table level or hydraulic head at a particular site.
piezometric level Syn: groundwater level.
piezometric surface Syn: potentiometric surface
Ð The level to which water in a confined aquifer will rise in observation
wells, mapped by interpolation between piezometer measurements.
Pito(t)meter Syn: Pitot tube
Ð A measuring device consisting of a delivery main entering a rigid conduit
with a diameter ensuring that flow takes place over the full cross section and
along a minimum length. At the end of the conduit, there is a section of tube
of diameter identical to that of the intake. The end of this tube is obstructed
a metal plate with a circular orifice at the centre. On the side of the tube, there
is a transparent manometer tube for the direct reading of discharge rate.
plasticity index (cf. Atterberg limits).
plutomium isotopes (cf. alpha-emitting actinides).
Ð A procedure based on the same principle as surging. Makes use of the forward
and return flow of groundwaters around the screen brought about by the large
volume of air introduced into the borehole. Two distinct methods can be
adopted: the open hole method and the closed hole method.
Ð Product containing chemical compounds with a high molecular weight resulting
from the association of several simple molecules having a low molecular
weight. Can be used directly as a drilling mud or as an additive to bentonic
mud, (cf. natural polymers).
Ð Addition of a solution of polyphosphate in order to break down the
cohesiveness of clay. Used to disperse mud cake, infiltrated mud or the clay
present in cutting samples, (cf. deflocculation).
Ð Phenomenon involving the displacement of fluids towards the well in order to
equilibrate the pressure. Appears during the recovery in water-level after
drawdown or cessation of pumping.
potentiometric surface , piezometric surface, water table
Ð The level to which water in a confined aquifer will rise in observation
wells. It is also the top surface of a groundwater body defined by the set of
piezometric levels measured at different points at a given date. Since this
surface corresponds to the upper boundary of the aquifer, it is the
hydrodynamic limit of the system, mapped by interpolation between piezometer
pressure head Syn: piezometric head
Ð Potential energy of a unit mass of water at any point compared with a
pressure of one atmosphere at the same elevation. Note: do not confuse with
e.g. attenuation zone, remedial action zone, well field management zone,
(cf. sanitary zone of well protection).
An exploratory borehole having an adequate diameter with respect to the fixed
objective can be subsequently equipped for water extraction use. Otherwise,
the hole can be re-bored so that it can be fitted out with a larger diameter
and transformed into a producing well.
pump discharge column Syn: rising main
Ð Tube used for extracting water from a well, connects the submersible pump
with the distribution network.
pumped water discharge
Ð The rate at which water can be pumped out of a well.
pumping discharge measurements Carried out by reading a calibrated flow
rate gauge (Pitot tube) or by measuring the time to fill a known volume.
Ð Yield obtained from a well during pumping.
pumping discharge head Syn: total static head.
pumping test analysis
Ð Procedure for interpreting data from pumping tests, usually based on the
graphical representation of drawdown vs. time curves and a comparison with
tabulated well functions, (e.g. Berkaloff, Boulton, Hantush, Jacob, Theis and
Walton methods). The experimental drawdown vs. time curve is superimposed on
standard curves in order to assess departures from the ideal state, (cf.
pumping tests , aquifer tests
Ð Procedure for measuring well efficiency, well performance or aquifer
characteristics, (e.g. step drawdown test, constant discharge test, absorption
test). Such tests make it possible to determine: the characteristics of an
aquifer/catchment structure; the hydrodynamic parameters; the operating
conditions of the well and the evolution of drawdown. Pumping tests performed
before the start of water abstraction or after a regeneration phase allow the
satisfactory completion of cleaning and development procedures, including
natural development, (cf. pumping test analysis).
Ð A measure of the ability of a given terrain to absorb a pollutant from the
groundwater, equivalent to the path length required for complete removal of
the pollutant from the liquid phase, (cf. effective transfer capacity).
quadratic head loss Syn: turbulent well loss. Symbol: CQ2
Ð Non-linear reductions in hydraulic head arising from turbulent flow within
the well structure, screen and casings. Quadratic head losses become all the
more important as the drawdown curve becomes increasingly convex .
quasi steady-state regime
Ð An eventual stabilization of the hydrological system in which the aquifer
restores its water balance.
quaternary ammonium compounds
Ð Strongly alkaline substances that are derived from ammonium by replacing one
or more of the four hydrogen atoms with organic radicals, (cf. ammonia).
radionuclide Syn: radioactive isotope.
Radioactive isotope tracers enable the estimation of turnover rates and circulation
flow rates for groundwaters, thus leading to the basic concept of residence time for
waters in an aquifer , (e.g. alpha-emitting actinides), (cf. radioactivity).
radius of influence (of well pumping) Syn: area of influence
Ð Zone within which water-levels are influenced by pumping. Corresponds to the
area of diversion in the restricted sense of TOLMAN, (cf. recharge area).
rainfall deficit , drought
rate of penetration Syn: drilling rate.
readjustment Syn: matching.
The use of gamma-ray logs is often necessary in order to enable a calibration
with the geological cross section.
recharge area Syn: intake area
Ð Zone located between radius of influence of well pumping and upstream
boundary of the hydrological system. Corresponds to undisturbed aquifer, (cf.
radius of influence).
redox potential Symbol: Eh
Ð A scale of electric potential measured in volts indicating the ability of a
substance or solution to cause reduction or oxidation reactions under a given
set of conditions. The higher the Eh, the more oxidizing are the conditions
and the greater is the capacity of the medium to accept electrons.
redox potential vs. pH diagram
Ð Plot of redox potential versus hydrogen potential used to display stability
of minerals or solutions in natural systems.
Ð Reverse of oxidation, being equally important in aerated groundwaters as in
Ð The volume of mobile water contained in the temporary zone of saturation,
remedial protection zone
Ð Immediate protected perimeter for pollution control around a water well.
Ð Technique based on data obtained from artificial satellites in Earth orbit.
The periods of the shots and the repetitivity of the information makes it
possible to select the images of most interest. Satellite imagery leads to a
better integration of major fractures (on the scale of several km), but the
lack of relief on these images hinders satisfactory correlation with the
ground truth, and the user is then obliged to fall back on conventional
methods. Where high groundwater discharges are sought, satellite imagery
can prove to be a valuable guide to the hydrogeologist in the selection of borehole
reserve Syn: storage
Ð Quantity of water contained in a hydrological system at a given date or
stored over a period of time, expressed in terms of volume (hm 3 or km 3). Four
types of storage are distinguished: total groundwater storage, regulating
storage, permanent storage and extractable storage. The groundwater storage is
evaluated using the volume of the slice of aquifer in question and either the
effective porosity (in the case of an unconfined aquifer) or the storage
coefficient (for a confined aquifer).
Ð The average time that formation waters remain in contact with a given volume
of rock, directly linked to the rate of infiltration of water within the
(c.f. convection time, transfer time).
Ð The coefficient r is proportional to the electrical resistance R of a
homogeneous conductor of length l and cross-sectional area s; if the current
density parallel to l is uniform and the temperature is constant, then R = r
l/s. The units of r are ohm.metre. The measurement of resistivity allows an
estimate to be made of the concentation of dissolved salts (or salinity) in a
water sample at a given temperature. It is also possible to determine the
amount of dissolved matter in a water/sediment mixture. Continuous on-line
recordings are commonly carried out with a resistivity meter, often in
combination with a nephelometer for turbidity measurement.
Ð Quantity of water that can be extracted from a defined volume over a given
period of time. Evaluation of the resource is based on the hydrodynamic and
hydrochemical behaviour of the aquifer, the resource is measured in terms of
mean discharge rate (m 3/s, hm 3/yr or km 3/yr).
restoration , regeneration, rehabilitation.
Ð System used for drilling large-diameter water wells in unconsolidated
formations. In the cleaning of holes with large diameters, the mud can be
injected into the annular space to bring up the cuttings inside the drill
Ð A dimensionless parameter which represents the ratio between forces of
inertia and forces of viscosity, i.e.: Re=v.d /V, where Re is the Reynolds
number, v is the Darcy velocity, d is the characteristic length and Vr the
kinematic viscosity. Serves to calculate the linear loss in head occurring in
a conduit under an established steady-state regime, assuming that the conduit
is rectilinear, the discharge rate is relatively stable and the diameter of
the conduit is homogeneous. The transition between laminar and turbulent flow
is a function of a large number of parameters, but it is generally accepted
that the laminar flow regime ceases for Reynolds numbers greater than unity,
(c.f. laminar flow, c.f. turbulent flow).
river bank effect
Ð Uptake of pollutants onto particulate matter as waters percolate through the
first few metres of river bank deposits towards the aquifer. Associated with
Rochelle salts (cf. additive).
A tool (drill bit) is attached to the end of a drill pipe string, and the
assembly is driven with a rotary movement at variable speeds and under vertical
compression. The rotary movement is transmitted to the drill string and to the
tool by a motor situated at the well-head. The drill pipes are hollow so that
mud can be injected into the bottom of the borehole.
run off, runoff
Ð Part of the precipitation flowing towards drainage systems into free bodies
Ð Chemical parameter commonly used in corrosion problems, equivalent to 2 pHS
Ð Chemical compounds formed by the reaction between an acid and a base, (e.g.
sulphates, chlorides). Ionic species present in water are derived in part from
the dissolution of minerals such as calcite, dolomite, gypsum and halite,
during their residence in the subsurface. Groundwaters take up a certain
number of mineral substances into solution, including limestone, dolomite,
gypsum, sodium chloride and potassium chloride, (cf. water chemistry).
Ð Clustering of grains in the gravel pack due to unidirectional flow, leading to reduced permeability.
The presence of sand in the mud can be harmful because of its abrasive action.
It also increases the mud density and, where there are significant deposits
the bottom, can cause blocking of the drill string; the permitted maximum sand content
in a mud is generally evaluated at 5%. Sand content can be measured with an elutriometer.
Ð Influx of sand into a well due to inappropriate design, screen corrosion or
overextraction. Can be treated by air-lift pumping, well scraping, surging,
sanitary zone of well protection , catchment protection zone
cf. protected perimeter.
saturated aquifer formation
Ð An aquifer whose reserve has been fully recharged. A saturated aquifer
formation will bring about dilution of the drilling fluid.
scale Syn: encrustation
scouring Syn: water flush
Ð Process by which well is cleaned by injection of water using compressed air,
(cf. air-lift development).
scraping Syn: brushing
Ð Method of well development making use of wall scratchers (e.g. porcupine
Ð A slotted or perforated liner placed in the well to control sand influx. The
screens should be placed adjacent to the points of greatest water inflow and,
generally speaking, over the entire thickness of the tapped aquifer zone, (cf.
bridge-slot scren, louvre-slot screen, Johnson-type screen).
Ð Movement of sediment particles into the well across the screen face, arises
from screen corrosion, overextraction or poor well design, (cf. sanding-up).
Ð Geophysical surveying method based on the recording of reflected seismic
waves, whose travel-times depend on the nature and structure of the geological
formations traversed. Although relatively little used in hydrogeology, small-scale
seismic reflection surveys can provide a valuable adjunct to seismic refraction,
covering a range of investigation from a few tens of metres to some hundred
metres depth, (cf. seismic refraction).
Ð Seismic surveying based on the study of travel-times of fully refracted
waves, depending on the nature and structure of geological formations.
Although seismic refraction suffers from some limitations, its use in
hydrogeology is preferred to seismic reflection because better results are
obtained in the depth range 0-200 m and the implementation is easier (cf.
Ð A process in which fine-grained material is washed away from the immediate
vicinity of the well. As a result, the flow velocity in the aquifer increases
near the well, thus leading to increased drawdown and enhanced performance. If
the 90-percentile is greater than 0.25 mm, then it is considered that the
formation can be developed naturally. This phenomenon is also termed
Ð Capacity of a given metal salt to combine with soluble species to form a
complex with covalent properties.
sodium hypochlorite Syn: Javel water.
solubility of gases
Ð Volume of a gas that can be absorbed by a volume of water depending on the
pressure and concentration of gases in the medium. Waters enter into contact
with gases especially in the zone of infiltration (e.g. only certain gases,
such as carbon dioxide, ammonia or hydrogen sulphide, exhibit high
solubilities). Being governed by Henry's law, gas solubility in water
decreases with increasing temperature and increasing salt concentration, (cf.
Ð Capacity of certain substances to form soluble complex salts, thus
incorporating insoluble species into their structure and promoting solvation.
This property is useful in solubilizing carbonate scale.
Ð Process in which the hydrating power of water (which is a strongly bipolar
molecule) leads to a partial or complete breaking of the various electrostatic
bonds between the atoms and the molecules of the substance entering solution,
thus forming new bonds and structures in the liquid state. Dissolution is said
to occur when solvation is complete, (cf. dissolution).
sonic log, acoustic well logging.
sorting coefficient Abbr: SC
Ð Quotient of the diameters of the 40- and 90-percentile classes on the
cumulative grain-size curve.
specific capacity (of a well)
Ð Discharge rate obtained per unit height of drawdown; it has the dimensions
of surface/time and is denoted as Q/s, (cf. specific drawdown curve).
specific drawdown Symbol: s/Q
Ð Drawdown level measured in the well divided by the pumped discharge; it is
expressed in m/m 3/h, being obtained from the equation of C.E. Jacob.
specific drawdown curve
Ð Plot of specific drawdown versus discharge used to analyse step drawdown
tests. Provides an estimate of aquifer and well losses, in addition to
information on transmissivity and storage coefficients, (cf. specific
specific yield (of an aquifer) Syn: effective porosity
Ð In the case of recharge, the volume of water that fills the available void
space of the porous medium per unit volume; in an unconfined aquifer, the
volume of water drained under the effect of gravity from the porous medium per
Ð Recent satellite that provides an improved image resolution at ground level
(30, 20 or 10 m) and offers the possibility of obtaining stereoscopic views.
As a result, such images can reveal just as must detail as aerial photographs
at a scale of 1:50,000.
Ð A square drill pipe.
Ð Physical mixture of liquid and gaseous components, in which the bubbles are
maintained in stable suspension. The foaming solution is sometimes
supplememented with polymers or bentonite in order to increase its density and
improve its viscosity qualities and also stabilize the borehole walls. The
foam must maintain a certain consistency, comparable to that of shaving foam.
standard electrode potential , equilibrium potential
Ð The potential of a couple in which the left-hand half cell is the standard
hydrogen electrode and the right-hand cell is the electrode system in question
(using 1M solutions at 1 atmosphere H 2 pressure, e.g.: Zn/Zn ++ (1M)//Cu ++
(1M)/Cu). Oxidation takes place at the left-hand half cell, (cf. electrochemical series).
standing water-level , rest water-level, standing level
Ð The level of the free water surface in an unpumped well or the piezometric
level of an unconfined aquifer. It corrseponds to the supposedly stable upper
surface of an undisturbed aquifer. In the case of an unconfined aquifer, the
standing water-level is always found beneath ground level; in the case of a
confined aquifer, the standing water-level remains virtual as long as a
borehole or a piezometer has not attained the aquifer, lying always above the
base of the overlying impermeable layer. It is also incorrectly termed static
static head , hydrostatic head
Ð Pressure exerted at any point in a liquid, represented by the height of the
overlying water column. Equivalent to pressure head plus elevation potential
energy, (cf. hydraulic head).
steady-state regime , equilibrium regime
Ð Regime in which, after a short pumping time, the geometry of the cone of
depression remains constant. In strict terms, the steady-state regime does not
exist except under exceptional conditions. In reality, the appearance of a
quasi-steady state regime is accepted for the purposes of calculation, (cf.
non-steady state regime).
step drawdown test
Ð Used to assess the efficiency and performance of a well, and to measure the
response of performance to varying discharge rate, (cf. pumping test).
Ð A sphere of radius r moving with velocity v through a large expanse of fluid
of viscosity n will experience an opposing force, or viscous drag, F, such that
F = 6p
. The equation describes the rate
of settling of solids particles in a
suspension or dispersion, but is valid only for restricted conditions (laminar flow
and low Reynolds number). In practice, corrections need to be made for boundary conditions.
Ð Parameter which characterizes an aquifer. Also known as storativity or bed
Ð A well where water rises from the confined aquifer but does not reach the
ground surface without pumping, (cf. artesian well).
Ð Strict anaerobes that obtain their source of energy by converting sulphate
to sulphide (e.g. Thiobacillus). These bacteria are ubiquitous in
groundwaters, soils and muds, but can only develop in the absence of oxygen
and at very low Eh values, (cf. iron bacteria).
Ð Chemical reaction between an electron-acceptor and sulphate ions to form
sulphide. A secondary phenomenon which can bring about modifications in the
chemical composition of groundwaters and lead to biological clogging; it is
associated with bacterial activity in de-oxygenated aquifers, (cf. sulphate-
Mainly derived from gypsum and anhydrite, as well as from the oxidation of
pyrites. Certain sulphates of magnesium or sodium can also be present in
Ð A surface-active substance used for its detergent properties.
surge block Syn: desanding plunger.
surging Syn: clearance pumping.
suspended particulate matter Abbr: SPM
Ð Sediment particles which do not settle out under normal conditions of flow.
The degree of swelling of marls increases with the alkalinity of the drilling
A swivel enables the bit to rotate on itself with each stroke.
Apart from fulfilling the required physico-chemical criteria, drinking water
should not have any odour or taste at a dilution factor of 2 or 3 .
Theis method , Theis's bi-logarithmic method
Ð Technique for the analysis of pumping tests assuming a fully confined
aquifer and no leakage from or into the aquifer. Used when the pumping time is
short, when the distance between the borehole and the observation well is very
large or in the case of pumping from an unconfined aquifer with a small
drawdown; in such circumstances, the data are difficult to treat with the
Jacob method, (cf. pumping test analysis).
e.g. a sodium polyacrylate base used in a 30% aqueous solution.
Ð Capacity for a mixture of particles in suspension to pass from a solid state
to a liquid state while being agitated and to return to its initial state when
the agitation ceases.
total alkalimetric titre Abbr: TAT, (cf. alkalinity).
Ð Maximum flow rate physically obtainable from a water well, being a function
of the local characteristics of the aquifer and the groundwater recharge. Also
known as potential yield or physical yield limit, (cf. water-yield).
total groundwater storage
Ð Quantity of mobile water contained in a volume comprised between the
substratum and the upper boundary of the aquifer. The mean total groundwater
storage is bounded at its top by the mean annual piezometric surface, (cf.
total static head , hydrostatic head, pumping discharge head
Ð Pressure exerted at any point in a liquid, represented by the height of the
overlying water column. It is equivalent to pressure head plus elevation
potential energy. The nature of the pumping equipment will vary according to
the expected discharge and the total static head and remains dependent upon
the diameter of the equipped borehole , (cf. hydraulic head).
Ð Chemical elements present in water whose concentration per unit volume does
not exceed a few tens of parts per million (ca. 0.01%), e.g.: Al, Fe, Mn, Ni,
Cr and Pb.
Ð The time taken for a tracer to travel from an intake point to a given
discharge in a hydrological system, (cf. convection time).
Ð A measure of the discharge of a water-bearing layer over its entire
thickness per unit width, subject to a unit hydraulic gradient. The discharge
capacity of a well in an aquifer depends on the hydraulic conductivity K and
the thickness e of the aquifer, the discharge capacity of a well can also be
estimated by means of a parameter T, denoting transmissivity, using the
equation: T = Ke, where: T is expressed in m²/s, K in m/s and e in m.
Transmissivity should not be confused with hydraulic conductivity, which is
calculated over unit thickness. Long pumping tests are used to calculate the
transmissivity, based on measurements of drawdown and recovery both in the
control well and also in observation wells.
Ð Cloudiness or opacity of fluid media caused by dispersion or absorption of
transmitted light, due to the presence of suspended particulate matter (clay,
silt, organic matter, plankton) or coloured chemical pollutants. The turbidity
of water becomes even greater with increasing amounts of colloid in
suspension; in practice, turbidity is evaluated by means of a nephelometer
which measures the intensity of light diffused laterally by the water sample.
The unit of measurement is the IU (International Unit), which corresponds to 1
mg of formazine per litre.
Turbulent flow may sometimes occur in the immediate proximity of a well, where
it arises from increased velocity of water circulation , (cf. Reynold's
turbulent well losses Syn: quadratic well losses.
Ð Mean annual recharge of the aquifer, IE, expressed in volume, divided by the
mean total groundwater storage, WM.
Ð Theoretical duration needed for the cumulative recharge volume of an aquifer
to become equal to its mean total storage, WM, which is equivalent to the
discharged volume of underground waters over the long term, QW; the turnover
time is expressed in years: WM/IE=WM/QW.
Ð A groundwater body having an upper boundary corresponding to a water table
that is free to fluctuate in response to hydrodynamic factors, (e.g. Champigny
Limestone, Beauce Limestone, Alsace valley alluvium, Lorraine karstic
limestone). The water-bearing formation is not saturated throughout its entire
thickness, (c.f. aquifer, confined aquifer, leaky aquifer).
unconfined groundwater body Syn: unconfined aquifer.
uniform inflow distribution
Ð A regular pattern of flow into a well, usually achieved by installing a
second screen with openings that ensure constant entrance velocity throughout
the tapped aquifer zones, (cf. entrance velocity).
unsaturated zone Syn: vadose zone
Ð Soil-water zone situated between the ground surface and the water table.
Water percolates rapidly downwards through this zone, and is not easily
extractible due to capillary forces, (cf. zone of infiltration).
unstable terrain , running ground
Ð Uncohesive formations with quicksand-like behaviour. Soft or unconsolidated
formations require feed pipes during drilling to prevent collapse.
verticality Syn: verticalness.
video camera inspection Syn: CCTV inspection.
e.g. viscosifier with a sodium acrylamide/acrylate copolymer base, biodegradable viscosifier.
viscosity (of drilling mud)
An appropriate choice of viscosity ensures a clean bit as well as the
efficient return to the surface and rapid settling out of drill cuttings.
Furthermore, it leads to a reduction in pressure-head loss in the drill
string. The viscosity of a mud can be measured with a Marsch viscometer (on
site) or a Stormer viscometer (in the laboratory).
void space volume
Ð Volume of air contained in pores, (cf. effective porosity).
Ð A method proposed by B. Walton makes it possible to characterize the
condition of a well in terms of its C value.
water balance Syn: water budget
Ð A measure of the difference between input and output flow rates in natural
hydrological systems. The global water budget is the amount of water involved
in the hydrological cycle each year. The calculation of a water balance
provides a means of checking the consistency of data with respect to the
recharge and flow behaviour within groundwater basins.
Ð Compositional specification of dissolved salts and gases present in water.
The composition of a particular water results from dissolution and chemical
reactions with substances present in the formations traversed by the water.
The concentation of dissolved substances in water may be expressed in terms of
the amount of gases, salts or ionic species per unit volume, (c.f. salts,
The colour of pumped out water is a parameter that can be readily estimated,
It is measured by comparing the tint of the sample with calibrated known
reference solutions. The results are expressed in colorimetric units or in
water cycle Syn: hydrological cycle
Ð Natural cycle in which water evaporating at the Earth's surface - mostly
from the oceans - passes into the atmosphere and falls back as precipitation.
Vast circulation process occurring at the surface of the Earth, including the
movement of water within the soil and subsoil; the origin, storage and flow of
groundwaters is controlled by the functionning of the hydrological cycle,
which can be represented as an equation taking account of the water balance:
P=E+R+I, where: E=evapotranspiration, P=precipitation, R=runoff and
water flush Syn: scouring
Ð Procedure for cleaning a well by water injection.
water hardness , hardness of water
Ð The quantity of calcium and magnesium salts contained in a water sample,
expressed as the equivalent mass of calcium carbonate dissolved in 1 litre.
The hardness of water is due mainly to the presence of calcium and magnesium
salts in the form of bicarbonates, sulphates and chlorides; a water hardness
of 1 corresponds to 10 mg/l on the French scale, 0.7 on the British scale.
water inflow Syn: influx
Ð Movement of water from tapped aquifers into a well.
water-level recorder , gauge
e.g. water-level dippers, pressure transducer system.
water-producing zone Syn: tapped aquifer zone
Ð Section of an aquifer that can be tapped by a well.
Ð Standards set by regulating authorities for the control of physical,
chemical and microbiological pollution in the drinking water supply (e.g.
colour, turbidity, taste, physico-chemical properties, undesirable substances,
toxic substances, bacteriology, pesticides). For each listed parameter, water
operators must ensure that the maximum permissible dose or level is not
Ð Product used to control loss of circulation.
water-yield Syn: capacity
Ð Flow rate of a well. Various types are defined, including safe yield,
potential yield and economic yield, (cf. total capacity).
Weighting up of mud is achieved by adding barite.
Ð Operation designed to repair damage to the well face and aquifer matrix
caused by drilling. Mainly aimed at removing cake from well walls and
improving the transmissivity of the near-field well environment in order to
restore the well's performance, (cf. aquifer development).
Ð Changes in permeability due to the influence of drilling mud. Becomes
apparent during phases of pumping. It is commonly observed in oil-wells, which
are almost always drilled with a rotary system and show productive capacities
that are relatively low. In the oil industry, it is customary to refer to this
phenomenon as the "skin effect."
Ð Group of wells designed for the abstaction of groundwaters from an aquifer.
well field management zone
Ð Far-field protected perimeter for pollution control around a well or group of wells
The well head should be built with great care since this determines the
staunchness of the catchment works, which represents a very important factor
in avoiding accidental pollution by surface waters. The well head should be
sufficiently ventilated so as to avoid condensation, which could also be a
source of pollution.
e.g. linear and quadratic.
Ð Plot of well discharge versus drawdown obtained from pumping tests.
zone of infiltration
Ð Unsaturated zone containing some air in its void space volume. It is located
between the water table and the ground surface, or up to the base of the
overlying aquitard where this exists, (cf. unsaturated zone).
zone of water-table fluctuation Syn: temporary zone of saturation
Ð Belt of oscillation of the free upper surface of a groundwater body.