NGWA CPI key terms

The drop in water level inside a well, measured from the static level, while the pump is running. It shows how much head the pump must overcome and how much the aquifer yields under pumping stress.

The undisturbed water level in a well when no pumping has occurred for a period and the water column has recovered. It is the reference point from which drawdown and pump setting depth are calculated.

The stabilized water level in a well measured while the pump is operating at its design rate. It determines the actual total dynamic head and confirms whether the pump setting is deep enough.

A saturated geological formation that can store and transmit enough groundwater to supply a well at useful rates. Its transmissivity and storage properties govern how much a well can sustainably produce.

A groundwater formation bounded above and below by low-permeability layers, so the water is under pressure. A well penetrating it may rise above the top of the aquifer, producing artesian flow.

The upper boundary of the saturated zone in an unconfined aquifer, where pore pressure equals atmospheric pressure. Its depth shifts seasonally and with nearby pumping, affecting shallow well yields.

The funnel-shaped lowering of the water table or pressure surface around a pumping well. Its shape reveals aquifer permeability and whether pumping is drawing water from nearby surface sources or other wells.

Well yield expressed as flow rate per unit of drawdown, such as gallons per minute per foot. Comparing it over time indicates aquifer performance, screen plugging, or declining well efficiency.

A slotted or perforated section of casing set opposite the producing formation that admits water while holding back formation material. Slot size and open area are matched to the gravel pack and aquifer grain size.

A graded filter of washed gravel or sand placed between the well screen and the borehole wall. It stabilizes the formation and limits sand entry while keeping head losses through the screen low.

The grouted, low-permeability annular seal placed around the casing near the surface to block surface water and shallow contamination from travelling down the borehole. It is a core public health requirement.

The gap between the borehole wall and the outside of the well casing. It is filled with grout, bentonite, or filter material, and its proper sealing prevents cross-connection between water-bearing zones.

The pipe installed in a borehole to keep the hole open and prevent collapse or caving. It also provides a pathway for the pump and a barrier against unwanted water entering the well.

The process of removing drilling mud, fines, and loose material from the screen and surrounding formation so the well produces clear water at its full capacity. It typically precedes a yield test.

A controlled pumping or bailing test that measures flow rate against drawdown to estimate sustainable capacity. Results guide pump sizing, setting depth, and the safe operating range for the well.

An accumulation of formation sand or gravel that blocks part of a screen or the borehole, reducing yield and sometimes jamming pumps. It often signals an undersized screen slot or excessive pumping velocity.

The mutual reduction in water levels when two or more pumping wells are close enough that their cones of depression overlap. It can cut yields even when each well performed well alone.

The total head a pump must develop while operating: the vertical lift, discharge pressure head, and all friction losses in pipe, fittings, and valves. Pump selection is based on this value at the design flow.

The vertical distance the water must be raised, measured from the pumping water level in the well to the discharge point. It is one component of total dynamic head and changes as drawdown changes.

Pressure energy lost as water moves through pipe, fittings, and valves, increasing with flow rate and pipe roughness. It is added to lift and pressure head when calculating total dynamic head.

A manufacturer's graph showing how head, efficiency, power, and sometimes net positive suction head vary with flow for a given impeller and speed. The duty point is where it crosses the system curve.

A plot of the head required by the piping system across a range of flow rates, combining static head and friction losses. The intersection with the pump curve defines the actual operating point.

The flow rate at which a pump converts input power to hydraulic work most efficiently, as shown on its curve. Operating near it reduces vibration, wear, and energy cost.

Relationships describing how changing impeller speed or diameter alters pump flow, head, and power. Flow varies with speed, head with the square of speed, and power with the cube of speed.

A multistage centrifugal pump coupled directly to a sealed electric motor and installed below the water level in a well. Motor cooling depends on adequate flow past the motor.

A pump that uses a venturi nozzle and diffuser, placed in the well or at the surface, to create suction and lift water. It suits shallow or low-yield wells and is configured as shallow or deep well.

The depth at which the pump intake is placed in the well, chosen to stay submerged during drawdown while leaving room for future water-level decline. Setting too shallow risks cavitation and dry running.

A one-way valve installed in the discharge piping that prevents backflow and keeps the drop pipe full when the pump stops. It protects the pump from water hammer and reverse rotation.

A pressure surge caused by a sudden change in flow velocity, such as rapid pump stop or valve closure. It can crack pipe, damage fittings, and shorten pump and motor life.

A vessel with a captive air charge that stores pressurized water and limits pump start-stop cycles. Correct precharge and tank sizing protect the motor and stabilize system pressure.

A device that starts and stops the pump at preset low and high pressure setpoints. Setting it correctly relative to tank precharge prevents short cycling and ensures adequate household pressure.

Rapid, repeated starting and stopping of a pump, usually from a waterlogged tank, wrong pressure switch settings, or an oversized pump. It overheats motors and shortens equipment life.

The minimum water velocity past a submersible motor needed to carry away heat. Manufacturers specify it, and low-yield wells may require a flow sleeve or a different pump selection.

An electronic controller that varies the voltage and frequency supplied to a pump motor, changing its speed to match demand. It maintains constant pressure and reduces starting current and cycling.

A device or setting that disconnects a pump motor when current exceeds a safe level or persists too long. Correct sizing prevents nuisance trips while protecting windings from burnout.

The current a pump motor consumes while running, measured with a clamp meter and compared with nameplate rating. High or unbalanced readings point to overload, low voltage, or a failing motor.

A measurement of motor winding and cable insulation resistance to ground, typically made with a megohmmeter before installation. Low readings warn of moisture intrusion or damaged cable.

A control device that monitors conditions such as current, voltage, or water level and shuts the pump off to prevent damage. It may include dry-run, overvoltage, and phase-loss protection.

A control feature that stops the pump when water level falls below the intake or when flow and pressure indicate no water. Running dry quickly overheats and destroys submersible motors.

The above-ground assembly at the top of a well, including the casing termination, cap or seal, and piping connections. A proper wellhead keeps contamination out and supports the drop pipe and wiring.