How to Interpret Results from Pump Drawdown Testing in Groundwater Wells

Pump drawdown testing is one of the most informative tools for understanding how a groundwater well performs under stress. Whether you’re managing a farm bore, planning new infrastructure, or overseeing a municipal supply system, correctly interpreting the results can help you optimize well performance, prevent damage, and ensure long-term reliability.

In this post, we’ll break down what a drawdown test is, what the results mean, and how to apply them in practical decision-making.

What Is a Pump Drawdown Test?

A pump drawdown test involves pumping water from a well at a constant or step-wise rate while measuring how much the water level (static water level) drops over time — this is the drawdown. The test typically includes:

• Pre-test measurements of static water level

• Pump activation at a known rate

• Recording water level changes at set time intervals

• Recovery phase, where the pump is shut off and water levels are monitored as they return to static

Key Terms to Understand

• Static Water Level (SWL): The undisturbed water level before pumping begins.

• Pumping Water Level (PWL): The water level in the well during pumping.

• Drawdown (DD): The difference between the static and pumping water levels (SWL - PWL).

• Discharge Rate (Q): The rate at which water is pumped, usually measured in litres per second (L/s) or gallons per minute (gpm).

• Specific Capacity (SC): The discharge rate divided by the drawdown (SC = Q/DD), indicating well efficiency.

Interpreting the Results

1. Drawdown Curve Behavior

A smooth and gradual drawdown curve suggests a well that is in good hydraulic connection with the aquifer. Rapid or excessive drawdown may indicate:

• Inadequate well design or screen placement

• Formation clogging or biofouling

• A poorly connected or low-yielding aquifer

2. Recovery Rate

The speed at which water levels return after pumping stops is just as important as the drawdown itself. A slow recovery may signal:

• Aquifer depletion

• Blockage or encrustation

• Overpumping stress

3. Specific Capacity Trends

Compare specific capacity values over time (especially with historical data). Declining specific capacity typically points to:

• Iron bacteria or biofilm buildup

• Mineral scaling (e.g. iron, calcium)

• Sand ingress or screen damage

A consistent or improving specific capacity indicates that your well is being maintained effectively.

4. Step Test Observations

If you conducted a step test (gradually increasing pumping rate in steps), you can:

• Plot discharge vs. drawdown

• Fit a Theis or Jacob analytical model to estimate aquifer transmissivity and well loss

• Detect thresholds beyond which the drawdown becomes nonlinear (often a warning sign of well inefficiency)

Practical Applications

• System Design: Choose appropriate pump sizes and flow rates that avoid excessive drawdown and pump damage.

• Maintenance Planning: Use trends to schedule redevelopment, chemical cleaning, or rehabilitation.

• Aquifer Health Monitoring: Assess sustainability of groundwater abstraction over time.

• Regulatory Compliance: Support licensing and reporting with robust performance data.

Red Flags to Watch For

Symptom	Possible Cause
Rapid drawdown with low flow	Encrustation, blockage, or poor aquifer connection
High drawdown but low recovery	Over-extraction or aquifer exhaustion
Specific capacity decline over time	Biofouling, scaling, or screen clogging
Water level does not recover fully	Permanent aquifer damage or compaction

Final Thoughts

Interpreting pump drawdown test results isn’t just about numbers — it’s about understanding the dynamic relationship between your well and the aquifer it taps. By carefully monitoring and analyzing these tests, you can extend the productive life of your groundwater assets and avoid costly surprises.

Need help interpreting your test data or planning a rehabilitation? Our team at Aquabiotics Industrial Pty Ltdspecializes in well performance diagnostics and sustainable water management solutions. Get in touch today for tailored support.

Written by: [David Bennett]Aquabiotics Industrial Pty Ltd