Low-Yield Well With a Pump That Cycles Every 40 Seconds

The equipment is mismatched to the well, and the breaker trips are a symptom, not the root cause.

Well versus pump:

• The well produced 6 gpm with drawdown from 60 to 115 feet, so specific capacity is about 0.11 gpm per foot of drawdown.
• The pump is rated at 12 gpm, double the tested yield. At 12 gpm, drawdown will be much greater than 55 feet. The water level will likely fall below the pump intake at 145 feet, so the pump will move air and lose cooling.
• A submersible pump that runs dry or pumps air overheats. That can trip the overload in the control box or the circuit breaker. The breaker trip must also be checked for voltage, wire size, and control-box condition, but cycling is the first problem to fix.

Tank volume:

• A 20-gallon bladder tank with a 30/50 switch has only about 5 gallons of usable drawdown.
• At 12 gpm, the pump would cycle in roughly 5 / 12 = 0.42 minute, or about 25 seconds. The reported 40 seconds is consistent with a pump that is not delivering full rate because it is cavitating or pulling air.

Conclusion: Increasing tank size alone would not correct the overpumping. The pump must be sized to the well yield, set at a depth that maintains submergence, and controlled so that it does not draw the water level below the intake.

The replacement should match the well, not the original 12-gpm demand.

Pump and setting:

• Select a 5-gpm pump rated for the required head. With the pump at 125 feet, static water at 60 feet, and 50 psi (about 115 feet) pressure, total dynamic head is roughly 180 to 200 feet, so a 1/2- or 3/4-hp, 5-gpm unit is appropriate.
• Set the pump at 125 feet. That is 10 feet below the 115-foot drawdown from the yield test and 25 feet above the top of the screen at 150 feet.
• Do not set the pump inside the screen interval. The screen is the aquifer connection, and a pump there can stir sand and damage the screen.

Tank and controls:

• Install a 44-gallon bladder tank. At 30/50, usable drawdown is about 11 gallons.
• At 5 gpm, cycle time is 11 / 5 = 2.2 minutes, which is acceptable. If the pump is set to 3 gpm, cycle time is about 3.7 minutes.
• Add a low-pressure cutoff, a check valve, a torque arrestor, and a pitless adapter. A cycle stop valve can help, but it does not substitute for a correctly sized pump and tank.

What not to do:

• Do not throttle the discharge with a gate valve as a permanent fix.
• Do not simply install a larger tank and keep the 12-gpm pump.
• Do not lower the pump below the screen to chase water.
• Do not upsize the breaker to stop tripping; find and correct the overload cause.

The well should be developed and tested before the final pump is selected, because the current yield test may not represent the developed well.

Development:

• Surging or airlifting should continue until the water is sand-free and turbidity is stable. The driller should measure sand content; persistent sand suggests screen damage or an unstable formation and may require a different screen or gravel pack.
• Development should not be so aggressive that it pulls formation material into the well.

Testing:

• Run a step-drawdown test at 2, 4, and 6 gpm to see whether specific capacity stays stable or declines at higher rates.
• Follow with a constant-rate test at the proposed pump rate, preferably 4 to 6 hours, and measure recovery. Record drawdown, pumping rate, and sand content.
• Use the results to set the pump depth and low-pressure cutoff. The specific capacity of about 0.11 gpm per foot means the well is sensitive to small increases in pumping rate.

Disinfection and sampling:

• Disinfect the well and pump assembly, flush, and wait the required period before sampling.
• Test for total coliform and E. coli, nitrate, and any local health department requirements such as arsenic. Do not place the well in service until the bacteriological result is satisfactory.
• Record the final pump setting, tank size, pressure switch settings, and test data in the well record.