5.2 Well Pumps, Wellhead Equipment & Source Protection

5.2 Well Pumps, Wellhead Equipment & Source Protection

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1. Pump types used on wells

Why suction lift is limited

Atmospheric pressure at sea level is 14.7 psi, which will support a column of water 14.7 × 2.31 = 33.9 feet. A real pump never gets that: subtract suction pipe friction, entrance and fitting losses, the vapor pressure of the water at its temperature, elevation above sea level, and the pump's own NPSH required. The practical working limit is 22 to 25 feet, and every foot beyond that pushes the pump toward cavitation. That is the physical reason deep wells use submersible or lineshaft turbines rather than suction-lift pumps.

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2. Setting and protecting the pump

• Pump setting must be deep enough to stay submerged at the maximum sustained pumping level, with margin for seasonal decline, but not so deep that it sits in the sump where sediment collects.
• Low-level protection. Level electrodes, pressure transducers, or flow switches stop the pump before it breaks suction. Running a submersible dry destroys the motor within minutes.
• Check valves. A check valve at the pump (and often intermediate checks in a deep column) prevents backspin and water hammer on shutdown. Backspin — restarting a pump while the column is still draining backward — shears shafts.
• Motor protection. Thermal overloads, phase-loss and phase-reversal relays, and undervoltage protection. On three-phase services, a single-phasing event is the most common cause of well motor burnout.
• Cycling. Frequent starts overheat motors and stress the aquifer near the screen. Submersible motor manufacturers publish maximum starts per hour by horsepower; soft starters and variable frequency drives reduce both inrush current and water hammer.

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3. Wellhead assembly the operator inspects

1. Sanitary well seal or watertight cap, bolted and gasketed.
2. Screened, downward-facing vent — confirm the screen is intact at every visit.
3. Casing above grade on a sloped pad that drains away, above the flood elevation.
4. Raw water sampling tap located before any treatment, so the operator can distinguish source problems from treatment problems.
5. Flow meter and totalizer, needed for both the monthly report and for computing specific capacity.
6. Air/vacuum relief valve on the discharge to prevent column collapse and to bleed air on startup.
7. Water level access — airline with gauge, sounder tube, or installed transducer.
8. Pressure gauge and pressure switch at the pump discharge; no unprotected hose bib or priming connection anywhere on the wellhead.

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4. Hydropneumatic tanks in small systems

A hydropneumatic (pressure) tank holds an air cushion over water so the pump can start and stop within a pressure band — typically a 20 psi differential, such as 40 psi on and 60 psi off.

• Function: prevents short-cycling and provides a small volume between pump starts.
• Limits: it is not equalization storage and not fire storage. Sizing is based on drawdown volume per cycle, not on demand.
• Maintenance: plain steel tanks lose their air cushion to dissolution and become "waterlogged," causing rapid cycling; they need an air volume control or periodic recharge. Bladder tanks avoid this but need the pre-charge pressure checked (set a few psi below cut-in) with the tank drained.

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5. Source water and wellhead protection

Treatment is the last barrier, not the first. North Carolina wellhead protection rests on:

• Separation distances from sewers, septic systems, animal operations, fuel storage, and other hazards — the gravity sewer criteria alone require 100 feet from any water supply source and never less than 50 feet from a public supply well.
• Proper abandonment of unused wells under 15A NCAC 02C, since an open abandoned well is a direct pipe into the aquifer.
• Source water assessments identifying the delineated area and potential contaminant sources for each intake and well, used to prioritize local protection measures.
• Routine sanitary surveys, which under the Ground Water Rule are a core compliance tool and which regularly turn up the same defects: unscreened vents, casings below grade, missing well caps, cross-connections at the wellhead, and unsealed abandoned wells on the same property.

[!NOTE] Tie it back to classification. A groundwater treatment facility with any single 18D .0203 parameter rated 10 points or higher — gas chlorine, caustic pH adjustment, packed tower aeration, gravity sand filtration — must be visited daily under 18C .1303(a)(2)(A). Adding a caustic feed to a small well system changes that system's visitation obligation permanently.