Irrigation Well Monthly Pump Performance & Aquifer Recovery Log

ContextA healthy submersible motor draws 5–7 times its rated full-load amperage for the first 1–3 seconds of startup—this inrush spike is normal and expected. What matters is whether the motor reaches running speed within 3 seconds and the amperage drops smoothly to the normal running range. If the motor hesitates, hums loudly, or trips the breaker on startup, you may be looking at a locked-rotor condition caused by worn bearings, a sand-locked impeller, or low supply voltage. Supply voltage below 90% of nameplate rating causes approximately 19% greater heat generation in motor windings per operating hour. Log the peak inrush reading each month; a creeping increase over consecutive months can signal increasing mechanical resistance long before an outright failure occurs.

ContextOn three-phase motors, all three legs should read within 5–10% of each other under stable load. A leg reading 15% or more above the others indicates phase imbalance—a condition that can cause the motor to run 10–30°C above its design temperature and dramatically compress winding life. Even a 3.5% voltage imbalance can translate to a 25% increase in winding temperature rise per NEMA standards. Compare each month's running amperage to the motor nameplate full-load amps (FLA): consistently running above FLA suggests pump wear or impeller damage is forcing the motor to work harder; running measurably below FLA on a well that previously drew normal amperage may mean worn impellers are no longer producing design head.

ContextIf one is not already installed, add a glycerin-filled pressure gauge at the wellhead discharge line—glycerin filling dampens vibration fatigue and extends gauge life significantly compared to dry gauges. Record pressure in PSI or bar at 15 and 30 minutes. Discharge pressure should stabilize once the system reaches hydraulic equilibrium; a continuing pressure drop after stabilization points to either a declining water level reducing pump submergence, or a worn impeller set that can no longer maintain design head. Cross-reference this reading with your concurrent drawdown measurement—pressure drops that correlate with rapid water level decline indicate the pump is approaching its minimum submergence limit and cavitation risk is building.

ContextA permanently installed totalizing flow meter is the gold standard—record its display reading over a timed interval and calculate gallons per minute (GPM). If none is installed, divert discharge into a calibrated tank and time how long it takes to fill a known volume. Compare this month's flow rate against the manufacturer's pump curve at the operating head your pressure gauge is showing. A 10% flow decline at equivalent head is a meaningful finding; a 20% decline indicates impeller wear or screen plugging that is increasing your energy cost per acre-inch of water delivered. Many state water-use permit conditions also require volumetric flow documentation on a seasonal or annual basis.

ContextCavitation sounds like gravel rolling inside a metal container and occurs when the pump draws faster than the formation can deliver water, causing vapor bubbles to implode violently on impeller surfaces. Untreated cavitation can destroy stainless steel impellers within a single irrigation season. Grinding typically points to bearing failure—submersible motor bearings are water-lubricated and fail rapidly if the pump runs dry even briefly. Cyclic pressure surging or rattling often indicates column pipe connections loosening due to torque imbalance in the pump string. Log the character, timing, and duration of any abnormal sound; even a 30-second cavitation episode at startup warrants a note, as the pattern across months can reveal a formation beginning to dewater faster than before.

ContextLower your electric sounder carefully while the pump is running—use a dedicated pumping-level sounder designed for dynamic conditions, or a weighted steel tape kept plumb with a heavy brass sinker. Record depth-to-water at each time interval from your fixed reference mark. Most unconfined aquifers show rapid initial drawdown in the first 15 minutes that slows and stabilizes as the cone of depression equilibrates with formation yield. If the water level continues dropping steadily past the 30-minute mark without any sign of stabilization, the formation yield may be insufficient for your current pump rate—a critical finding that may require restructuring your irrigation schedule to allow longer recovery windows between pump cycles.

ContextDrawdown equals the pumping water level depth minus the static water level depth at 60 minutes. For example, if static level is 85 feet below the reference and pumping level at 60 minutes is 112 feet, drawdown is 27 feet. This number quantifies the hydraulic stress being placed on the aquifer during your operating cycle. Compare it month-to-month at the same flow rate: drawdown that increases at identical pump output over consecutive months indicates declining aquifer transmissivity or shrinking saturated thickness in the screened formation. A sudden increase of more than 30% above your historical average at the same flow rate warrants immediate investigation before continuing to pump at current rates.

ContextSpecific capacity (SC) equals GPM divided by feet of drawdown. At 180 GPM and 27 feet of drawdown, SC is 6.67 GPM per foot. This metric normalizes flow against aquifer response, making sessions with different static levels directly comparable to one another. A declining SC trend over 12–24 months is the most reliable early warning of either well screen clogging from biofouling or mineral incrustation, or progressive aquifer depletion. Screen rehabilitation caught early—chemical treatment, jetting, or brushing—typically costs $1,500–$5,000. Waiting until SC decline exceeds 50% substantially reduces rehabilitation success rates, and full well replacement in agricultural settings typically runs $50,000–$200,000 or more depending on depth and casing diameter.

ContextMost submersible pump manufacturers specify a minimum submergence of 5–10 feet of water above the pump intake at all times during operation—the motor housing depends on water flowing past it for cooling, and inadequate submergence causes thermal runaway in motor windings within minutes. If your drawdown readings approach this margin, immediately throttle the flow control valve to reduce extraction by 20–25%, note the restricted rate and resultant stabilized water level in the log, and assess whether the pump needs to be set deeper or the daily pumping schedule needs restructuring. Document every throttle adjustment by date and flow rate—these records form the factual basis for any conversation with a pump engineer about resizing the installation.

ContextBrief turbidity during the first 30–60 seconds after a long shutdown is expected as settled sediment resuspends in the column pipe. What is diagnostically significant is turbidity that persists beyond 5 minutes, or that is visibly worse than in prior months—this can indicate a deteriorating well screen, a failed gravel pack, or formation material migrating into the casing. Reddish-brown coloration suggests iron oxidation, often tied to seasonal redox chemistry changes in the aquifer. Milky or chalky discharge points to clay intrusion or carbonate mobilization. Either form of sustained discoloration warrants a laboratory turbidity test (measured in NTU, typically under $50) to establish a quantified baseline for future comparison.

ContextUse a handheld EC or TDS meter and record in µS/cm or parts per million. Most irrigation-quality groundwater falls in the range of 200–1,500 µS/cm. Readings above 3,000 µS/cm impose osmotic stress that reduces yield in sensitive crops, and above 5,000 µS/cm most vegetables and many field crops face significant suppression. Monthly EC readings are essential for catching saltwater intrusion in coastal aquifers and for detecting upward migration of deep saline water when drawdown is excessive. A sudden EC increase of 25% or more versus your baseline is a red flag requiring a full water chemistry panel—typically $150–$300—before continuing to irrigate, to protect both crop health and long-term soil structure.

ContextFill a clean 1-liter clear glass or plastic bottle with discharge water and let it stand undisturbed for 5 minutes; any sand or grit will settle visibly at the bottom. The presence of sand—even a thin layer—must be taken seriously regardless of how minor it appears. A pump moving just 1 tablespoon of sand per hour will show measurable impeller and wear-ring abrasion within a single irrigation season, shortening pump life from a typical 10–15 years to under 2 years. Estimate the settled volume in milliliters and record it each month. Any reading above 5 mL per liter warrants suspending operation for a professional screen and gravel pack inspection before the next irrigation cycle begins.

ContextGroundwater temperature in deep confined aquifers is stable year-round, typically within 1–2°C of the local mean annual air temperature. A sudden rise of 3°C or more in discharge temperature relative to your baseline—not ambient air—can indicate surface water infiltrating the well by bypassing the annular seal or through a casing integrity failure. In shallow water-table wells, temperature variation simply reflects seasonal soil warming and is less diagnostically significant on its own, though still worth tracking consistently. A persistent deviation from your historical seasonal range for this calendar month is one of the low-cost early indicators of a surface contamination pathway that warrants further investigation.

ContextThe moment the pump stops, note both the time and the water level—this establishes the start point of your recovery curve. If you hear loud pipe banging or water hammer on shutdown, the check valve may be failing or missing; water hammer stress fractures threaded fittings and can rupture PVC discharge pipe, particularly at union joints. A functioning check valve eliminates column backflow and should produce a clean, quiet shutdown with no significant banging. Log any hammering episode because repeated water hammer events gradually fatigue pipe threads and welded fittings even when no visible damage occurs after a single event.

ContextUse the same sounder and reference point used for drawdown measurements. The shape of the recovery curve is as diagnostically valuable as the drawdown curve itself. A productive sandy-gravel aquifer might recover 80% of drawdown within 30 minutes; a low-permeability fine-grained formation may require 4–6 hours for full recovery. What you are watching for is a change in the shape of your recovery curve versus your historical records at the same time intervals: slower recovery at the same drawdown amount suggests either declining hydraulic conductivity from screen clogging or a reduction in available saturated thickness in the formation. Always record in feet below the reference point, not as feet recovered, to maintain consistency with your drawdown data.

ContextResidual drawdown equals the water level at 60 minutes after shutdown minus the pre-pump static water level. In a healthy, high-yield well, residual drawdown at the 60-minute mark should be less than 25% of the session's original total drawdown. If the aquifer is still showing more than 50% of original drawdown at one hour post-shutdown, either the formation has inherently low transmissivity (a characteristic you can track across years) or the value is worsening—indicating progressive aquifer stress. This metric is especially useful for wells serving multiple irrigation pivots in the same field, as it tells you whether inter-cycle recovery windows are sufficient to maintain safe pump submergence during the next scheduled run.

ContextFull recovery to pre-pump static level within 6 hours is a practical benchmark for a healthy well under typical agricultural pump rates. If full recovery now requires significantly longer than your historical norm for the same drawdown—say 4 hours when it used to take 2—you are watching aquifer performance degrade in measurable increments in real time. This trend data provides the factual foundation for conversations with regulatory agencies about groundwater basin sustainability, and for decisions about restructuring pump schedules to shift some extraction to overnight hours when regional aquifer pressure is generally higher across a heavily pumped basin.

ContextVariable frequency drives (VFDs) and modern soft-start controllers maintain internal fault histories even after self-resetting. Access the fault log and transcribe any codes triggered since your last monthly check, whether or not they caused an observable interruption. Priority fault categories include overvoltage and undervoltage events (pointing to utility supply quality problems), ground fault codes (possible winding insulation breakdown requiring a motor rewind at $500–$3,000 or full replacement at $1,000–$8,000+ depending on horsepower), and thermal overload trips. One thermal trip during a heat wave may reflect ambient conditions; monthly trips indicate an underlying cause—undersized supply conductors, blocked motor cooling flow, or a pump working well above its rated operating point.

ContextA low-water protection device—whether a float switch, pressure-transducer controller, or current-sensing relay—is the last line of defense against a dry-run event that can destroy a submersible motor in under 30 minutes at full load. To test: temporarily restrict flow to simulate low-water conditions and verify the controller trips and locks out within its programmed threshold. Reset and confirm auto-restart behavior if the system uses a timed restart sequence. Many operators discover during this test that the protection device has been bypassed by field staff to maintain irrigation schedules—a dangerous workaround. Confirm the trip delay setting matches manufacturer specification, typically 30–90 seconds for agricultural submersible applications.

ContextTake voltage readings at the motor control center bus bars with the pump running at full operating load—not at idle, when voltage will appear artificially high. Acceptable operating voltage for most three-phase agricultural motors is ±10% of nameplate (for a 460V motor: 414–506V on every leg). Voltage sagging below 90% of nameplate consistently during peak summer afternoons is a utility supply problem worth formally reporting to your power company, as sustained low voltage accelerates winding insulation degradation and may void the motor warranty. Calculate voltage imbalance: divide the maximum deviation from the average by the average, then multiply by 100. Any imbalance above 2% warrants investigation with your utility or electrical contractor.

ContextCross-check the hour meter reading against your irrigation schedule records. If the meter is not advancing or shows an implausible reading, it may have failed—a small issue with large consequences, since all preventive maintenance intervals are calculated from total operating hours. Standard submersible motor bearing life ranges from 2,000 hours in high-sand environments to 8,000 hours in clean-water wells. Mark your maintenance calendar in advance: schedule a pump pull and inspection at 2,000 cumulative hours for wells with any sand history, and at 4,000 hours for clean-water applications, regardless of whether pump performance still appears normal at that point.

ContextLook for surface staining that indicates ongoing slow leaks: rust streaks from steel components, white carbonate deposits from hard water, or green verdigris from copper fittings. Pay close attention to threaded connections and union joints, which fail first in systems with high iron content or water pH below 7.0. Even a minor drip of 1 GPH wastes over 700 gallons per month and slowly erodes the wellhead pad concrete across a season. For any PVC discharge piping exposed to sunlight, check for UV degradation—a chalky or flaking surface texture means the material has become brittle and may fail under pump pressure without warning, and should be replaced with UV-stabilized material or wrapped with protective insulation.

ContextCheck pre-charge with the system fully depressurized (pump off, tank pressure bled down) using a standard tire gauge at the Schrader valve. The pre-charge should be set to 2 PSI below the pressure switch cut-in setting. If it is too high, the tank provides almost no useful drawdown volume and causes the pump to short-cycle—running for only a few seconds at a time—dramatically accelerating wear on motor starting components and capacitors. A pre-charge that declines from month to month indicates a slow bladder leak; replacement bladder or diaphragm kits typically cost $80–$300 and are far cheaper than replacing the full pressure tank ($300–$1,200) or accelerated motor failure from short-cycling.

ContextProper surface drainage should slope away from the wellhead casing at a minimum gradient of 1 inch per foot for the first 3 feet in all directions. Flat or low-lying wellheads that collect water during irrigation or rainfall create a direct pathway for pesticide and nitrate contamination, especially in sandy soils with rapid infiltration rates. Check for ground squirrel or gopher burrow openings within 5 feet of the casing—these animals frequently burrow alongside casings, creating preferential flow channels that can route surface water past the annular grout seal and directly toward the water table. Document and photograph any grading deficiencies or burrow activity and address them before the next significant rainfall event.

ContextA single month's specific capacity reading has almost no diagnostic value on its own; its entire worth lies in the trend it contributes to. Create a simple line chart with months on the horizontal axis and SC in GPM per foot on the vertical axis—even hand-drawn graph paper works. A healthy well in a stable aquifer shows a relatively flat SC trend with seasonal variation of ±10–15%. A downward trend exceeding 20% over 12 months, absent any operational changes, is a reliable early warning of screen incrustation or aquifer depletion that warrants professional evaluation. A stepwise drop—SC that was 7.2 for months and suddenly falls to 5.1 in one reading—more likely signals a discrete mechanical event such as a broken screen section or partial sand bridge rather than a gradual aquifer change.

ContextAquifer performance is strongly seasonal in most regions—drawdown is naturally greater during peak summer demand when neighboring wells, municipal supply, and natural evapotranspiration losses all compete for the same formation water. Comparing June to June and September to September across years—rather than month-to-month within the same year—removes seasonal noise and isolates genuine year-over-year aquifer trends. This same-calendar-month comparison has revealed multi-year aquifer declines in several documented western basin studies that were completely invisible in within-year comparisons. Keep prior-year logs accessible at the pump house for this review—the 3-minute comparison pays dividends that no other single diagnostic step can replicate.

ContextDefine your baseline as the average of the same calendar month across all prior years you have records for, with a minimum of 2 years of data for any statistical validity. A 15% threshold balances sensitivity against false alarms from normal variability. Readings that should trigger immediate follow-up rather than watchful waiting: static water level more than 5 feet below seasonal baseline, specific capacity below 75% of seasonal baseline, running amperage above 110% of motor nameplate FLA, or EC more than 125% above baseline. For each flagged reading, document the deviation value, your assessment of the probable cause, and the action taken—even if that action is continued monitoring. This creates a defensible maintenance history that carries weight in insurance claims, equipment warranty disputes, and water rights proceedings.

ContextThe physical copy serves field staff and maintenance crews during any emergency response when devices may be unavailable. Off-site digital storage—a scanned PDF uploaded to cloud storage, emailed to a management office, or entered into farm management software—protects against fire, flooding, or rodent damage to the pump house. Many state water agencies increasingly require pumping logs as a condition of continued water use permits; in prior-appropriation western states, your records are legal documentation of your water right exercise and must be produced in formal water rights proceedings. Use a consistent log format month to month so any staff member can complete it accurately without interpretation, and date and sign every entry—an unsigned entry has reduced evidentiary value in any formal proceeding.