7.15 Well and Wellhead Maintenance, Sanitary Condition, Rehabilitation & AWWA C654 Disinfection
Key Takeaways
- Static and pumping water levels recorded consistently give drawdown and specific capacity, which is the most valuable trend a well operator maintains.
- Declining specific capacity with an unchanged static level indicates screen incrustation or biofouling and calls for well rehabilitation rather than a larger pump.
- A well casing terminating in a below-grade pit that can flood is a recognized significant deficiency, as are a missing sanitary cap gasket and an unscreened vent.
- Frequent starts destroy submersible motors, so pressure tank sizing and level control bands must respect the motor's maximum starts per day and minimum run time.
- Any work that opens a well requires AWWA C654 disinfection at roughly 100 mg/L with satisfactory bacteriological samples before return to service, and the chlorinated waste must be dechlorinated.
Where the water enters the distribution system
WPI's distribution outline lists "understand wells and related equipment, including measuring static water levels and pumping water levels," "maintain well and related equipment," and "maintain the sanitary condition of the well." For the many Colorado systems whose only source is a well and whose only operator holds a distribution or Class S certificate, these tasks are the entire source-side job.
Well and pump equipment
| Component | Function | Maintenance concern |
|---|---|---|
| Casing | Isolates the borehole; extends above grade | Corrosion, perforation, cracked welds |
| Annular seal (grout) | Prevents surface water migrating down the outside of the casing | Failure allows direct contamination |
| Screen or open hole | Admits water while excluding formation material | Incrustation, biofouling, sand production |
| Gravel pack | Filters and stabilizes the formation | Plugging; settlement requiring re-packing |
| Submersible pump | Motor and bowls below water; power by drop cable | Motor lead splice failure, overheating on low flow |
| Vertical line shaft turbine | Motor at surface, bowls below water, driven by a shaft | Line shaft bearing lubrication, packing, alignment |
| Pitless adapter | Below-frost discharge connection through the casing | Seal failure allowing surface water entry |
| Well seal or sanitary cap | Seals the casing top around wiring and piping | Cracked or missing gasket |
| Vent | Downturned, 24-mesh screened | Missing screen; insect and rodent entry |
| Check valve | Holds column water and prevents backspin | Failed valve causing water hammer and backspin damage |
| Air/vacuum relief | Releases air on startup, admits air on shutdown | Stuck valve; must be above flood level and screened |
| Flow meter, pressure gauge, sample tap | Monitoring and compliance | Meter accuracy; sample tap ahead of treatment |
| Water level access port or air line | Static and pumping level measurement | Blocked port; leaking air line |
Routine well operations
Measure and record water levels. Static level before startup after adequate recovery, and pumping level after the level stabilizes. From those two numbers, compute drawdown and specific capacity and trend them. This is the single most valuable well record an operator keeps.
Watch the electrical signature. Falling amperage with falling discharge pressure suggests loss of submergence, a worn pump, or a broken shaft. Rising amperage suggests a bound pump, sand, or a failing motor. Insulation resistance (megger) testing on submersible motor leads catches insulation breakdown before a failure.
Control cycling. Frequent starts destroy motors. Submersible motors are rated for a maximum number of starts per day and a minimum run time so the motor cools. Short cycling from an undersized pressure tank or a narrow level band is a leading cause of premature failure.
Prevent sand pumping. Sand destroys pump bowls, meters, valves, and check valves and carries into the distribution system. Persistent sand means a screen or gravel pack problem, or a pump set too deep or oversized for the well.
Avoid over-pumping. Drawing the level below the pump intake breaks suction, and drawing it into the screen causes cascading water, air entrainment, and accelerated incrustation. Set low-level cutouts and respect the well's sustainable yield.
Sanitary condition
The listed job task is explicit: maintain the sanitary condition of the well. The requirements mirror the sanitary survey checklist:
- Casing terminating above grade — commonly at least 12 inches above the finished floor or ground, and above the highest known flood elevation.
- A sealed sanitary well cap or seal with intact gasket where wiring and piping pass through.
- A downturned, 24-mesh screened vent.
- An intact annular grout seal.
- Ground sloped away from the wellhead; no pit that can flood. Well pits are a recognized significant deficiency, since a flooded pit surrounds the casing top with contaminated water.
- Discharge to waste with an air gap, never a submerged or directly connected drain.
- A raw water sample tap ahead of treatment.
- Secure, locked access and appropriate site fencing.
- Chemical storage, fuel tanks, and vehicle parking kept away from the wellhead.
Well rehabilitation and disinfection
Declining specific capacity at an unchanged static level points to the well rather than the aquifer. Rehabilitation methods:
- Mechanical: surge blocks, brushing, high-pressure jetting, and airlift development to break loose and remove incrustation.
- Chemical: acid treatment (typically inhibited hydrochloric or sulfamic) to dissolve carbonate and iron scale, or chlorine and specialized biocides for iron bacteria and biofouling. Chemical work requires careful neutralization and lawful disposal of the spent solution.
- Combination, alternating chemical soak with mechanical agitation, is generally most effective.
Disinfection under AWWA C654 applies whenever a well is newly constructed, has the pump pulled, is repaired, or is otherwise opened. The general practice is to introduce a chlorine solution to achieve a concentration on the order of 100 mg/L throughout the water column and gravel pack, circulate or surge it so it contacts all surfaces, hold it for the specified period, then pump the well to waste until the chlorine is dissipated. Satisfactory bacteriological samples are required before the well returns to service, and the highly chlorinated water pumped to waste must be dechlorinated before it reaches a storm drain or watercourse.
A well's specific capacity has declined steadily while its static water level has remained unchanged. Which rehabilitation approach addresses the likely cause?
Which wellhead condition is a recognized significant deficiency on a sanitary survey?
After a well pump is pulled and reinstalled, what must occur before the well can return to service?