How to Perform Pump Drawdown Tests in Groundwater Wells

Pump drawdown testing is an essential step in assessing the performance and capacity of a groundwater well. It provides crucial insights into how the well and surrounding aquifer behave under pumping stress, helping well owners and operators make informed decisions about design, rehabilitation, or long-term usage.

Whether you're planning a new well installation or troubleshooting an existing one, here’s how to properly conduct a pump drawdown test.

🔍 What Is a Pump Drawdown Test?

A drawdown test involves pumping a well at a constant rate and measuring the decline in water level (the drawdown) over time. This test reveals:

• The efficiency of the well

• The yield of the aquifer

• Potential issues such as well screen clogging or aquifer depletion

🧰 Equipment You’ll Need

Before beginning the test, make sure you have the following:

• Submersible or line shaft pump (with known and controllable flow rate)

• Water level measurement tools (electric sounder, pressure transducer or data logger)

• Flow meter (mechanical, ultrasonic, or electromagnetic)

• Stopwatch or time-logging device

• Discharge pipe with appropriate fittings

• Recording sheets or digital data logging system

🛠️ Step-by-Step Procedure

1. Baseline Measurements

• Measure and record the static water level (SWL) — the level of water in the well before pumping starts.

• Inspect the wellhead for access ports and ensure safe working conditions.

2. Pump Setup

• Install the pump at a depth below the expected drawdown level (usually 3–5 m above the well screen or pump intake zone).

• Connect the discharge piping and install the flow meter.

3. Begin Pumping

• Start the pump and adjust to a constant target discharge rate. This rate should be sustainable for the test duration and realistic for well use.

• Record the start time precisely.

4. Monitor Water Levels

• Measure water level drawdown at consistent time intervals. A typical schedule might be:

  • Every minute for the first 10 minutes

  • Every 5 minutes for the next 30 minutes

  • Every 15 minutes for the remainder of the test (e.g., for a 2–4 hour test)

• Continue pumping until the water level stabilizes (i.e., change is less than a few centimeters over 30 minutes) or for a predetermined test duration.

5. Recovery Phase

• After shutting off the pump, begin measuring water level recovery at similar time intervals.

• Continue monitoring until the water level returns close to static level, or a stable recovery curve is reached.

📊 Analyzing the Results

• Drawdown (s) is calculated as:

  
  

  s = SWL - PWL

  
  

  where PWL is the pumping water level at a given time.

• Plot drawdown vs. time on a semi-log graph for well efficiency and aquifer response evaluation.

• Use methods such as Theis or Cooper-Jacob analysis to interpret transmissivity and storativity if aquifer parameters are needed.

✅ Best Practices

• Always calibrate flow meters and logging equipment before the test.

• Test during stable aquifer conditions (avoid rainy periods or nearby pumping events).

• Record atmospheric conditions, site notes, and any anomalies.

• Repeat tests periodically to track well performance over time.

🧪 When Should You Conduct a Drawdown Test?

• After well construction or redevelopment

• During routine maintenance checks

• If you suspect reduced yield or screen clogging

• Before designing a permanent pump system

⚠️ Common Pitfalls to Avoid

• Inconsistent pumping rate during the test

• Incorrect depth setting of the pump

• Insufficient measurement intervals (missing early-time data)

• Not allowing enough recovery time post-test

Conclusion

Pump drawdown testing is a powerful tool in groundwater management. When done correctly, it provides actionable data that supports sustainable pumping, efficient well design, and long-term aquifer health.

If you're unsure about interpreting the results or conducting the test safely, it's best to engage a professional hydrogeologist or well contractor with field experience.