Water Well Driller cheat sheet

Holding capacity of a borehole annulus: annular velocity must carry cuttings upward; cuttings settle when upward fluid velocity drops below the particle settling velocity, so pump rate and annular area govern hole cleaning.

Rotary mud circulation pressure loss rises with mud viscosity, hole depth, and pump rate; a sudden loss of returns with a pressure drop signals a lost-circulation zone or a fractured formation.

Cable-tool drilling advances by crushing and bailing; casing is driven as the hole deepens, and the bit string must be kept free of sand to avoid stuck tools.

Well screen open area should exceed the formation's inflow area; slot or screen opening is sized to retain the target formation gradation, typically passing 50-70 percent of the filter pack.

Filter (gravel) pack is sized at roughly 4 to 6 times the D50 of the formation sand for uniform sand, and the pack thickness is typically 3 to 8 inches in the annulus.

Casing centralizers and annular grout volume: neat cement yield is about 1.15 cubic feet per 94-pound sack, so sacks equal annular volume divided by that yield, with excess for washouts.

Static water level is measured before pumping; pumping water level is measured during sustained yield testing; drawdown equals pumping level minus static level.

Specific capacity equals pumping rate divided by drawdown, expressed in gallons per minute per foot; declining specific capacity over time indicates screen plugging or aquifer depletion.

Total dynamic head equals pumping lift plus discharge pressure head plus friction losses in drop pipe, fittings, and discharge lines; pump selection must meet TDH at the design flow rate.

Submersible pump setting depth must keep the pump above the well bottom and below the pumping water level by enough submergence to prevent vortexing and motor overheating.

Motor sizing: brake horsepower equals flow in gallons per minute times TDH in feet divided by 3960, then divided by pump efficiency; add a safety margin for motor selection.

Drop pipe friction loss increases with flow squared; undersized drop pipe can consume a large share of available head and reduce delivered flow.

Check valve placement: a check valve above the pump holds column water and prevents backspin; additional check valves along the drop pipe reduce water hammer but can trap pressure between them.

Wire sizing for submersible motors is set by voltage drop limits, commonly 5 percent maximum at the motor terminals; ampacity and voltage drop both constrain conductor size.

Pump rotation and wiring: three-phase submersible motors reverse when any two leads are swapped; verify rotation before sustained operation to avoid damage.

Sanitary well seal and pitless adapter: the seal must be watertight around the drop pipe and wiring, and the pitless adapter must be installed below the frost line to prevent freezing.