What is Borehole Efficiency Testing?
A borehole efficiency test, also known as a pumping test or aquifer performance test, is a controlled procedure that evaluates how your borehole performs under pumping conditions. It measures the relationship between pumping rate, drawdown (the drop in water level), and recovery. The goal is to determine the borehole's sustainable yield, hydraulic characteristics, and overall efficiency.
During the test, a pump is installed in the borehole, and water is extracted at a known rate while water levels are monitored at specific intervals. The data collected allows hydrogeologists to calculate key parameters such as specific capacity, transmissivity, and well losses, which together indicate the health and productivity of the borehole.
Efficiency testing is not just for new boreholes; it is equally important for existing ones to detect performance decline, plan for rehabilitation, or size a replacement pump correctly.
Why Efficiency Testing Matters
Investing in a borehole is a significant financial commitment. Efficiency testing ensures you get the maximum return on that investment. Here are the key reasons why testing is essential:
- Determines sustainable yield – reveals the maximum rate at which water can be pumped without depleting the aquifer or causing excessive drawdown.
- Identifies performance issues – detects problems like screen clogging, development issues, or incorrect pump sizing.
- Informs pump selection – accurate data ensures the pump is neither over‑ nor under‑sized, saving energy and extending equipment life.
- Monitors long‑term health – repeated tests over time can track gradual decline, allowing proactive maintenance.
- Compliance and warranty – many lenders and insurance providers require efficiency data, and some contractors offer warranties conditional on a successful test.
In Kenya, where groundwater resources are increasingly pressured, efficiency testing also supports sustainable water management by ensuring that each borehole operates within safe limits.
Types of Efficiency Tests
Three main types of pumping tests are used to evaluate borehole efficiency. Each provides different insights, and they are often performed in sequence.
| Test Type | Purpose | Duration | Key Outputs |
|---|---|---|---|
| Step‑Drawdown Test | Determines the relationship between pumping rate and drawdown; identifies optimal pumping rate and well losses. | Several hours (steps of 30–60 min each) | Specific capacity, well efficiency, step‑drawdown curves |
| Constant‑Rate Pumping Test | Measures aquifer hydraulic properties (transmissivity, storativity) and confirms sustainable yield. | Typically 24–72 hours (or longer) | Transmissivity, storativity, drawdown curves |
| Recovery Test | Measures how quickly water levels return to normal after pumping stops; indicates formation permeability and well efficiency. | 1–2 times the pumping duration | Transmissivity (from recovery data), aquifer recharge rate |
In practice, a complete efficiency test program usually includes all three: step‑drawdown, then constant‑rate, followed by recovery. This comprehensive approach gives the most reliable picture of borehole and aquifer performance.
Key Metrics: Specific Capacity & Efficiency
Two critical metrics derived from efficiency tests are specific capacity and well efficiency.
Specific Capacity
Specific capacity is the pumping rate (in m³/hr) divided by the corresponding drawdown (in metres) at a given time. It is expressed as m³/hr/m. A higher specific capacity means the borehole yields more water per metre of drawdown, indicating better productivity. For example, a borehole that pumps 10 m³/hr with a drawdown of 5 m has a specific capacity of 2 m³/hr/m.
Monitoring specific capacity over time is a powerful diagnostic tool. A significant decrease often points to clogging, screen damage, or aquifer depletion.
Well Efficiency
Well efficiency is the ratio of the actual drawdown in the borehole to the theoretical drawdown that would occur if the well were 100% efficient (i.e., no head losses from friction or turbulent flow). It is expressed as a percentage. An efficiency of 70–80% is considered good; below 50% indicates significant losses that may require rehabilitation.
Low efficiency results in higher pumping costs, reduced yield, and accelerated wear on the pump. Efficiency testing helps identify these issues so they can be addressed before they become critical.
How to Interpret Test Results
Interpreting efficiency test results requires expertise, but understanding the basics can help you engage confidently with your contractor.
- Drawdown behaviour – if drawdown increases rapidly even at moderate pumping rates, the aquifer may have low permeability or the well may be poorly developed.
- Specific capacity trend – a declining trend over multiple tests suggests progressive clogging or screen incrustation.
- Recovery rate – quick recovery after pumping indicates good connection to the aquifer and high transmissivity; slow recovery suggests limited recharge or poor well design.
- Step‑drawdown analysis – if drawdown increases disproportionately with each step, it indicates turbulent flow losses (often due to screen entry velocity issues or gravel pack problems).
A professional hydrogeologist will provide a detailed report with graphs, calculations, and recommendations. This report is invaluable for pump sizing, system design, and long‑term management.
How WaterLink Limited Conducts Efficiency Testing
WaterLink Limited follows rigorous, internationally recognised standards for borehole efficiency testing (ISO 14686 and Kenyan WRA guidelines). Our approach ensures accurate, repeatable data that you can trust.
- In‑house hydrogeologists – our tests are designed and supervised by certified hydrogeologists with decades of experience in Kenya's diverse geology.
- Modern instrumentation – we use electronic pressure transducers, flow meters, and data loggers for high‑precision measurements.
- Customised test design – each test is tailored to the specific borehole and aquifer conditions, ensuring relevant and actionable results.
- Comprehensive reporting – you receive a detailed report with raw data, analysed curves, calculated parameters, and clear recommendations.
- Compliance and licensing – all our tests comply with WRA and NEMA requirements, making it easier for you to obtain permits and approvals.
We believe that thorough testing is the foundation of a successful borehole. That's why we include a fully instrumented efficiency test as part of our standard drilling package, giving you peace of mind from day one.
Common Problems Revealed by Efficiency Testing
Efficiency testing often uncovers hidden issues that would otherwise lead to premature failure or poor performance. Some of the most common problems include:
- Screen clogging – caused by fine sand or mineral precipitation, reducing water entry and increasing drawdown.
- Gravel pack settling – improper gravel pack can cause voids or compaction, affecting well efficiency.
- Pump mis‑sizing – an oversized pump can cause excessive drawdown and turbulent flow, while an undersized pump may not meet demand.
- Aquifer depletion – if the pumping rate exceeds the aquifer's recharge capacity, efficiency will decline over time.
- Damage to casing or screen – corrosion, physical damage, or poor installation can create leaks or restrict flow.
Early detection through efficiency testing allows you to take corrective action—such as rehabilitation, pump adjustment, or even re‑drilling—saving you from costly failures and downtime.
