NGWA CWD key terms

A slotted or perforated pipe section installed at the producing zone of a water well that admits water while holding back formation material, sized to the aquifer's grain size.

Selected sand or gravel placed in the annulus around a well screen to stabilize the formation, improve flow, and prevent fine particles from entering the well.

The gap between the borehole wall and the outside of the casing or drill pipe, which is filled with grout, filter material, or drilling fluid depending on well design.

An impermeable barrier of grout or clay placed in the annular space, usually at the top of the well, to prevent surface water and shallow groundwater from moving down the borehole.

A cement-based or bentonite-based slurry pumped into the annular space to seal the borehole, set casing, and block vertical movement of water between aquifers.

The level at which water stands in a well when the pump is off and the water table has stabilized, measured from a fixed reference such as the top of casing or ground surface.

The water level in a well while it is being pumped at a steady rate, lower than the static level because of drawdown around the borehole.

The difference between the static water level and the pumping water level in a well, expressed in feet or meters and used to evaluate well performance.

A well's yield per unit of drawdown, usually reported in gallons per minute per foot, calculated by dividing pumping rate by drawdown after the well stabilizes.

A controlled pumping test that measures well discharge and water-level response over time to estimate safe yield, specific capacity, and the effects of pumping on nearby wells.

A confined aquifer in which water is under pressure because the recharge area is higher than the top of the aquifer, so water rises in a well above the aquifer top.

A low-permeability stratum such as clay or dense rock that restricts water movement into or out of an aquifer and separates it from adjacent aquifers.

A saturated geologic formation that can store and transmit water in usable quantities to a well or spring.

The upper surface of the saturated zone in an unconfined aquifer, where pore pressure equals atmospheric pressure and which rises and falls with recharge and discharge.

The capacity of a geologic material to transmit water through its interconnected pore spaces, controlling how readily a well can be supplied by the surrounding formation.

The fraction of a rock or sediment volume made up of voids, which determines how much water the material can store but not how fast it moves.

A liquid or slurry circulated during drilling to cool the bit, carry cuttings to the surface, stabilize the borehole wall, and control formation pressure.

The density of drilling fluid, commonly reported in pounds per gallon, which must be high enough to control formation pressure but not so high that it fractures the formation.

The condition in which drilling fluid escapes into a permeable or fractured formation instead of returning to the surface, reducing hole cleaning and risking stuck tools.

Rock fragments and sediment removed from the bottom of the borehole by the drill bit and carried to the surface by the drilling fluid or air stream.

The speed at which the bit advances through formation, usually expressed in feet per minute or feet per hour, and used to judge formation changes and bit condition.

The downward force applied to the drill bit during rotary drilling, which affects penetration rate, hole straightness, and bit wear.

The rate at which the drill string and bit rotate, measured in revolutions per minute, and matched to formation type and bit design for efficient cutting.

The assembly of drill pipe, drill collars, and tools that transmits rotation and drilling fluid from the rig to the bit.

Steel or plastic pipe installed in a borehole to keep the hole open, prevent caving, isolate aquifers, and provide a sealed conduit for the pump and water.

The process of pumping cement slurry into the annular space around casing to bond the pipe to the formation, seal off water zones, and protect the casing.

A grout mix of cement and water without sand or aggregate, commonly used for well seals because it forms a strong, low-permeability barrier.

A grout or bentonite seal placed at the ground surface around the casing to prevent surface runoff and shallow contamination from entering the well.

The process of removing drilling mud, fines, and disturbed material from the formation around a screen so the well produces clear water at its full capacity.

A well development method that repeatedly reverses flow through the screen to loosen and flush fine material from the filter pack and adjacent formation.

A development technique that injects compressed air into the well to lift water and create surging action that clears fines from the screen and filter pack.

A graded gravel envelope placed around a screen in unconsolidated formations to increase effective well diameter, control sand production, and improve yield.

A blockage formed when formation sand or filter material packs tightly in the annulus or inside the screen, restricting flow and sometimes stopping the pump.

The width of the openings in a well screen, selected so the filter pack or formation is retained while water enters freely, usually expressed in thousandths of an inch.

An imaginary surface representing the level to which water would rise in tightly cased wells completed in a confined aquifer, reflecting the pressure head in that aquifer.

A well completed in a confined aquifer where the potentiometric surface stands above ground level, so water discharges without pumping.

The pressure exerted by a column of water or drilling fluid at a given depth, increasing with depth and fluid density and balanced against formation pressure during drilling.

A crack or parting created in rock when fluid pressure in the borehole exceeds the rock's strength, which can cause lost circulation and unwanted vertical water movement.