Author Archives: Raeli Hydro

A borehole is not a set-and-forget infrastructure asset. Like any mechanical and civil system exposed to a dynamic natural environment, it requires ongoing attention to remain safe, productive, and efficient. Boreholes that receive regular maintenance and monitoring consistently outperform those that are neglected, delivering better water quality, longer equipment life, and more reliable yields over their operational life.

The Case for Proactive Management

The most common cause of borehole failure is not geological — it is neglect. Fine particles gradually clog screens, bacterial colonies establish themselves on pump components, water levels shift with seasonal and long-term aquifer changes, and pump wear slowly degrades performance. None of these processes happen overnight, and all of them can be detected early if the right monitoring systems are in place.

Early detection means early intervention — which is almost always cheaper, faster, and less disruptive than emergency repair or full rehabilitation. The cost of a monitoring programme is typically a small fraction of the cost of a single rehabilitation event.

Core Components of a Maintenance & Monitoring Programme

1. Water Level Monitoring

Regular measurement of both the rest water level (static level when the pump is off) and the pumping water level (dynamic level during pumping) provides the most fundamental indicator of borehole and aquifer health. Rising rest levels may indicate aquifer recharge; falling levels may signal over-abstraction or regional drought. Widening drawdown — the difference between rest and pumping levels — at the same pumping rate indicates increasing borehole resistance, typically caused by screen blockage or pump inefficiency.

Water levels should be measured manually on a regular schedule and automatically logged if a data logger is installed.

2. Yield and Flow Rate Monitoring

The volume of water the borehole produces per unit time is its most operationally important parameter. Flow rate should be measured regularly using a calibrated flowmeter installed on the discharge line. Declining flow at a constant pump setting, combined with stable or falling water levels, indicates a problem with the pump. Declining flow combined with increasing drawdown suggests borehole or aquifer deterioration.

3. Water Quality Monitoring

Routine water quality sampling should cover, at minimum:

• Bacteriological parameters — total coliforms and E. coli as indicators of contamination.
• Physical parameters — turbidity, colour, and taste, which can signal casing or screen deterioration.
• Chemical parameters — key indicators such as pH, electrical conductivity, nitrate, iron, and manganese, monitored for trends over time.

Sudden changes in quality — particularly turbidity spikes or bacteriological positives — require immediate investigation and action.

4. Pump and Electrical System Checks

The submersible pump is the most mechanically complex and failure-prone component of the system. Regular checks should include:

• Motor amperage and power consumption (rising amps at the same output indicate wear)
• Pump efficiency testing (comparing flow rate and head against the original pump curve)
• Inspection of visible components: rising main, cable, wellhead seals, and surface discharge pipework
• Testing of control panels, protection relays, and safety switches

5. Wellhead Inspection

The wellhead is the first line of defence against surface contamination entering the borehole. It should be inspected regularly for:

• Integrity of the sanitary seal and cap
• Absence of standing water or ponding around the wellhead
• Condition of the concrete apron or headworks
• Security of locks and access controls

Monitoring Frequency

The appropriate frequency of monitoring depends on the importance of the borehole, its operational intensity, and the sensitivity of the aquifer. A general framework:

• Weekly: Visual wellhead inspection, flow rate check, operational observations.
• Monthly: Water level measurement, pump performance check.
• Quarterly: Basic water quality sampling (bacteriological and physical parameters).
• Annually: Comprehensive water quality analysis, pump efficiency test, review of all monitoring data trends.
• Every 3–5 years: Full borehole inspection using a downhole camera, CCTV survey of casing and screen condition.

Record Keeping

Monitoring is only as useful as the records it generates. All measurements, observations, and test results should be recorded in a maintenance logbook or digital database, with date, time, and the name of the person conducting the check. Trend analysis — plotting measurements over time — is the most powerful tool for identifying gradual changes that no single measurement would reveal.

A well-kept maintenance record also provides the documentation needed to support insurance claims, regulatory compliance, and asset valuation.

 

 

 

Every borehole drilling project operates under uncertainty. The subsurface cannot be fully known in advance; contractors may underperform; weather can disrupt operations; equipment can fail; regulations can change. Risk management is the structured process of identifying, assessing, and responding to these uncertainties before they become crises. In a sector where a single dry borehole can consume an entire project budget, good risk management is not optional — it is essential.

What is Risk in a Borehole Project?

A risk is any uncertain event or condition that, if it occurs, would affect one or more project objectives: scope, cost, time, quality, or safety. Risks can be:

• Geological risks: Deeper-than-anticipated aquifer depth; absence of groundwater in target zone; unexpected hard formation; contaminated aquifer.
• Technical risks: Equipment breakdown; loss of circulation; borehole collapse; screen installation problems.
• Contractor risks: Poor performance; delayed mobilisation; financial difficulties leading to abandonment.
• Regulatory and legal risks: Permit delays; changes in licensing conditions; land access disputes.
• Environmental risks: Contamination of nearby water sources; improper disposal of drilling waste.
• Financial risks: Currency fluctuation; material price escalation; cost overruns.
• Social risks: Community opposition; land ownership disputes; security issues at the site.

The Risk Management Process

Step 1: Risk Identification

The first step is a systematic review of all activities and conditions in the project to identify what could go wrong. This is best done as a structured workshop involving the project team, the supervising hydrogeologist, and — where possible — experienced local practitioners who know the specific area and its challenges.

A risk register is the standard tool: a structured table in which each identified risk is recorded, described, and assigned to an owner who is responsible for monitoring and managing it.

Step 2: Risk Assessment

Each risk is assessed on two dimensions:

• Likelihood: How probable is it that this risk will materialise? (High / Medium / Low, or a probability percentage.)
• Impact: If it does materialise, how seriously would it affect the project? (High / Medium / Low, or a cost/time estimate.)

The combination of likelihood and impact gives each risk a risk rating — the product of the two scores — which is used to prioritise management attention. High-likelihood, high-impact risks demand immediate and robust treatment; low-likelihood, low-impact risks can be monitored passively.

Step 3: Risk Response

For each significant risk, a response strategy is defined:

• Avoid: Change the project plan to eliminate the risk entirely. For example, relocating a proposed borehole site away from a contaminated area.
• Mitigate: Take action to reduce the likelihood or impact of the risk. For example, conducting more thorough geophysical investigation to reduce the probability of a dry hole.
• Transfer: Shift the financial consequences of a risk to another party. For example, using a lump sum contract for defined scope items, or requiring the contractor to carry performance bonds.
• Accept: Acknowledge the risk and set aside contingency to absorb it if it occurs. This is appropriate for residual risks that cannot be further reduced cost-effectively.

Contingency Planning

Contingency planning addresses the question: what do we do if a specific risk materialises? For the most consequential risks in a borehole project, a pre-planned response avoids reactive, costly improvisation.

Dry Borehole Contingency: Define in advance the decision criteria for declaring a borehole unproductive (e.g., yield below a minimum threshold after full development), the process for drilling a replacement borehole, and the budget provision for this outcome.

Equipment Failure Contingency: Identify alternative rig sources that could be mobilised within an acceptable timeframe if the primary rig breaks down. Include an equipment downtime provision in the project programme.

Contaminated Water Contingency: Specify the water quality parameters that would trigger an alternative water source investigation, and identify what those alternatives might be.

Permit Delay Contingency: Allow buffer time in the project programme for regulatory processes, and identify early engagement strategies to prevent avoidable delays.

Contingency Budget

The contingency budget is the financial expression of residual risk — the funds held in reserve to absorb costs arising from risk events that cannot be fully mitigated. Determining the appropriate contingency level requires judgement, informed by:

• The quality and completeness of pre-drilling investigation.
• The complexity of the geology and the variability of groundwater occurrence in the area.
• The track record and reliability of the contractor.
• The experience of the project management team.

Contingency is not a slush fund and should not be used for scope changes or foreseeable costs that were simply omitted from the base estimate. It is drawn down only against defined risk events, with each draw documented and approved.

Risk Communication

Effective risk management requires that risks and their status are communicated to the right people. The client, funder, and oversight bodies should understand the principal risks before the project starts, not be surprised when they materialise. Regular project reports should include an updated risk register showing changes in risk status, mitigating actions taken, and any contingency drawn down.

Transparency about risk builds trust. A project manager who proactively identifies and manages risks, and communicates clearly when they occur, is far more credible and effective than one who obscures problems until they become crises.

 

Over time, even well-constructed and properly maintained boreholes experience declining performance. Screens become blocked, bacterial films colonise pump components, encrustation forms on casing walls, and physical deterioration of the borehole structure reduces hydraulic efficiency. Borehole rehabilitation is the process of restoring a deteriorated or failing well to acceptable operational performance — and in many cases, it is far more cost-effective than drilling a new borehole.

When is Rehabilitation Warranted?

Rehabilitation should be considered when one or more of the following is observed:

• Significant decline in specific capacity (yield per unit drawdown) compared to baseline measurements.
• Increasing turbidity or sand content in the pumped water.
• Deteriorating water quality — particularly rising iron, manganese, or bacterial counts.
• Visible corrosion, joint displacement, or collapse detected by CCTV inspection.
• Pump failure caused by abrasion from fine sediment entry.
• Extended period of non-use with no record of prior maintenance.

A thorough diagnosis precedes rehabilitation. CCTV inspection, pumping tests, and water quality analysis together define the nature and extent of the problem, which in turn determines the appropriate rehabilitation approach.

1. Mechanical Redevelopment

For boreholes where screen blockage or gravel pack compaction is the primary problem, mechanical redevelopment is the first-line technique. This involves surging, jetting, or air lifting — the same methods used in initial borehole development — applied more intensively to dislodge accumulated fines and restore hydraulic conductivity.

Mechanical redevelopment is low-cost and non-invasive. It is most effective when the screen and casing remain structurally intact and the problem is primarily accumulation rather than mineralogical encrustation.

2. Chemical Treatment

Where encrustation or biofouling is the dominant problem, chemical treatment is required to dissolve or disperse the blocking material.

Acid treatment (typically hydrochloric or sulfamic acid) dissolves carbonate, iron oxide, and manganese oxide encrustations that have formed on screen slots and in the gravel pack. The acid is introduced into the borehole in a calculated dose, allowed to react for a defined contact period, and then purged by pumping to waste.

Polyphosphate and dispersant treatments break up clay and silt bridges that have formed in fine-grained formations. They are gentler than acid treatment and suitable for formations or screen materials that would be damaged by acid.

Biocide treatment targets iron-related bacteria and other biofilm-forming organisms. Chlorine is the standard biocide for water wells, but in severe biofouling cases, more concentrated shock chlorination or specialist biocide products may be required.

Chemical treatments are most effective when followed immediately by mechanical redevelopment to remove the loosened or dissolved material before it can resettle.

3. High-Pressure Jetting

High-pressure jetting during rehabilitation uses the same principle as during initial development but at greater intensity and with more targeted application. Specialist jetting tools direct pressurised water at specific screen intervals identified as blocked by CCTV inspection, physically clearing slot obstructions and penetrating into the gravel pack.

When combined with simultaneous air lifting or pumping to remove dislodged material, high-pressure jetting can restore screen open area close to its original condition.

4. Liner Installation

Where CCTV inspection reveals structural damage to the casing — corrosion holes, joint failure, or partial collapse — the compromised section must be addressed to prevent contamination ingress and further deterioration. In many cases, a liner (a smaller diameter casing inserted inside the damaged section) can seal the defect without requiring full casing replacement.

Liner installation reduces the internal diameter of the borehole, which may affect pump sizing and yield. However, it is usually far less disruptive and expensive than casing replacement or redrilling.

5. Screen Replacement

If the screen is irreparably blocked or physically damaged — corroded through, collapsed, or encrusted beyond the reach of chemical and mechanical treatment — it may need to be replaced. This is a complex operation involving removal of the pump and rising main, extraction of the existing screen (where possible), and installation of a new screen assembly.

The feasibility of screen replacement depends heavily on the borehole construction and the depth and nature of the damage. In some cases, it is more cost-effective to seal the existing borehole and drill a new one adjacent to it.

6. Pump and Rising Main Replacement

In many rehabilitation scenarios, the borehole structure itself is sound but the pump and rising main have deteriorated to the point of failure. Pump replacement is a relatively straightforward operation that can restore full yield quickly, provided the borehole itself is performing adequately.

Before reinstalling a new pump following any rehabilitation work, the borehole should always be thoroughly redeveloped and disinfected to avoid contaminating the new equipment.

Post-Rehabilitation Assessment

Rehabilitation is complete only when the borehole has been tested and the results demonstrate improved performance. A pumping test conducted after rehabilitation, and compared against the original commissioning test data, quantifies the improvement achieved and establishes a new performance baseline. Water quality sampling confirms that chemical treatments have been fully flushed and that the borehole is bacteriologically safe before return to service.

 

 

 

Two of the most common and insidious processes that reduce borehole performance over time are incrustation and biofouling. Both are natural phenomena driven by the chemistry and biology of groundwater, and both are manageable — but only if understood and addressed systematically. Left unchecked, they can reduce yield, degrade water quality, and ultimately cause irreversible blockage of screens and gravel packs.

Incrustation: Mineral Build-Up

Incrustation is the deposition of mineral solids on borehole screens, casing walls, pump components, and rising mains. It occurs when changes in pressure, temperature, or chemical equilibrium cause dissolved minerals to precipitate out of solution.

Iron and manganese incrustation is the most common type in groundwater systems. Groundwater often contains dissolved iron (Fe²⁺) and manganese (Mn²⁺) in anaerobic conditions. When this water is pumped and comes into contact with oxygen — at the screen face, in the pump, or in the distribution system — the iron and manganese oxidise and precipitate as reddish-brown or black solids. These deposits coat screen slots and gravel packs, progressively restricting flow.

Carbonate incrustation (calcium and magnesium carbonate) forms when hard water experiences a drop in CO₂ partial pressure, driving carbonate precipitation. This is most pronounced near the pump intake and in rising mains, where pressure changes are greatest.

Silica scaling is less common but can occur in certain geochemical environments, producing hard, glassy deposits that are particularly resistant to treatment.

Biofouling: Biological Clogging

Biofouling is the growth of microbial communities — primarily bacteria — within the borehole, screen, and gravel pack. While all groundwater contains bacteria, certain species thrive in the conditions created by pumping and can cause significant operational problems.

Iron-related bacteria (IRB) — principally Gallionella ferruginea and Leptothrix ochracea — oxidise dissolved iron to form gelatinous iron hydroxide sheaths as a metabolic byproduct. These sheaths accumulate rapidly, forming thick, slimy deposits that trap other particles and clog screens far faster than purely chemical iron precipitation would.

Sulphate-reducing bacteria (SRB) thrive in anaerobic conditions and produce hydrogen sulphide as a metabolic byproduct — responsible for the rotten egg smell occasionally encountered in borehole water. They also produce corrosive conditions that accelerate metal casing and screen deterioration.

Slime-forming bacteria produce extracellular polymeric substances (EPS) that form sticky biofilms on surfaces. These films trap fine particles, further compounding clogging.

Recognising the Problem

Signs of incrustation and biofouling include:

• Declining specific capacity without corresponding change in regional water levels
• Red, brown, or black discolouration of pumped water
• Slime or sediment deposits in storage tanks and distribution pipework
• Sulphurous odour in the water
• Rapid pump wear due to abrasive particles
• CCTV inspection revealing coated or partially blocked screen slots

Prevention and Control Strategies

Regular Redevelopment

The most effective prevention strategy is regular mechanical redevelopment — surging, jetting, or air lifting — before accumulations become severe. Redevelopment at 1–2 year intervals (depending on the severity of the chemistry and biology of the specific aquifer) dislodges material before it has time to consolidate into hardened deposits.

Shock Chlorination for Biofouling

Periodic shock chlorination — introducing a high-concentration chlorine dose and allowing extended contact time — is effective in controlling IRB and other biofilm-forming organisms. The recommended approach for active biofouling uses concentrations of 200–500 mg/L free chlorine, held for 12–24 hours, followed by vigorous mechanical development and thorough flushing.

A single treatment is rarely sufficient. Biofouling management typically requires repeated treatment cycles until bacterial populations are suppressed, followed by a regular maintenance chlorination schedule (typically annually or biannually).

Acid Treatment for Chemical Incrustation

Hydrochloric acid (HCl) at 5–15% concentration is effective in dissolving iron oxide, manganese oxide, and carbonate deposits. The acid is introduced in a targeted dose calculated to the volume of the treated zone, allowed to react, and then purged completely. In heavily incrustated boreholes, multiple acid treatment cycles may be required.

Acid treatment must be followed immediately by mechanical development to remove dissolved material and by thorough flushing before return to service. Careful handling, neutralisation, and disposal of spent acid are mandatory.

Polyphosphate Sequestration

In boreholes with moderate iron concentrations where incrustation is a persistent maintenance issue, continuous or periodic dosing of polyphosphate can sequester dissolved iron and manganese, keeping them in solution and preventing precipitation. This does not treat existing deposits but helps prevent new ones forming. It must be used cautiously in drinking water applications, as polyphosphate doses must remain within acceptable limits.

Monitoring for Early Detection

The most cost-effective approach to managing incrustation and biofouling is detecting them early. Quarterly measurement of specific capacity (yield per unit drawdown) and regular turbidity monitoring will reveal the onset of clogging before it becomes severe. When specific capacity falls more than 25% below the baseline established at commissioning, investigation and treatment should begin promptly.

 

 

 

Water level is the single most informative measurement that can be made in a borehole. It integrates the behaviour of the aquifer, the performance of the borehole, and the effects of pumping into one continuous, measurable parameter. A well-maintained water level dataset is the foundation of informed borehole management — enabling early detection of problems, supporting abstraction licence compliance, and building the long-term understanding of aquifer behaviour that underpins sustainable groundwater use.

What Water Level Data Tells Us

Rest Water Level (Static Level)

The rest water level — measured when the pump has been off for a sufficient period for the borehole to fully recover — reflects the ambient pressure head of the aquifer at that location. Changes in rest level over time reveal:

• Seasonal recharge patterns: Rising levels in wet seasons, falling levels in dry seasons.
• Long-term aquifer trends: Persistent decline may indicate over-abstraction or reduced recharge from climate or land-use change.
• Regional pumping effects: Nearby high-volume abstraction can depress local water levels.

Pumping Water Level (Dynamic Level)

The pumping water level — measured during active pumping — combined with the rest water level gives the drawdown: the depth the water level is depressed below rest during pumping. Drawdown analysis reveals:

• Borehole efficiency: A widening drawdown at a constant pumping rate indicates increasing resistance in the borehole or pump system.
• Aquifer transmissivity: The rate and shape of drawdown development during a pumping test characterises aquifer hydraulic properties.
• Safe yield limits: The maximum drawdown before the pump intake is exposed or the yield becomes unstable defines the operational limits of the borehole.

Manual Water Level Measurement

The simplest and most widely used method for measuring water level is the electric contact dipper (also called a water level meter or e-dipper). This is a graduated cable with a probe at the end that completes an electrical circuit and triggers an audible or visual signal when it contacts water. The depth reading is taken from the cable graduation at the top of the casing.

Manual measurement is low-cost, reliable, and requires no power. It is the standard method for periodic monitoring visits. For accurate and comparable results:

• Always measure from the same reference point (typically the top of the casing).
• Allow sufficient rest time before measuring static levels (typically 4–24 hours after pumping stops, depending on the aquifer).
• Record the date, time, and pumping status alongside each measurement.

Continuous Data Logging

For boreholes where detailed, high-resolution water level data is required — operational wells, aquifer monitoring points, or research boreholes — continuous data loggers are installed. These devices measure and record water level at defined intervals (typically every 15–60 minutes) without human intervention, providing a complete record of aquifer behaviour over time.

Types of Data Loggers

Pressure transducer loggers are the most common type. A sealed pressure sensor is suspended below the water surface at a fixed depth. It measures the pressure exerted by the column of water above it, which is converted to water depth. Vented loggers compensate for atmospheric pressure changes automatically; non-vented loggers require barometric correction during data processing.

Float-operated loggers use a float and pulley to mechanically track the water surface. They are reliable and easy to understand but less accurate in deep or narrow boreholes and more susceptible to mechanical failure.

Shaft encoder loggers are used with a float and counterweight system and record float position electronically. They are well-suited to large-diameter wells with significant water level variation.

Data Storage and Retrieval

Most loggers store data internally on flash memory and are downloaded periodically via a data cable or Bluetooth connection to a laptop or field device. Increasingly, loggers are equipped with GSM or satellite telemetry that transmits data in real time to a remote server or cloud platform, enabling continuous remote monitoring without site visits.

Data Management and Analysis

Raw water level data is only useful when it is properly managed and analysed. Best practice includes:

• Consistent naming and units: All data files should be named with the borehole identifier, date, and measurement units clearly recorded.
• Barometric correction: Non-vented logger data must be corrected for atmospheric pressure variation before analysis.
• Plotting time series: Graphing water level against time reveals seasonal patterns, event responses, and long-term trends that are invisible in tables of numbers.
• Specific capacity calculation: Dividing yield by drawdown at regular intervals tracks borehole efficiency over time.
• Anomaly investigation: Sudden step changes, unexplained fluctuations, or persistent declining trends should trigger field investigation.

Integration with Abstraction Compliance

In regulated environments, water level monitoring is often a condition of the abstraction licence. Operators must demonstrate that abstraction is not exceeding sustainable limits, and water level data provides the evidence. Long-term datasets submitted to regulatory authorities also contribute to the regional groundwater monitoring networks that underpin basin-scale water resource management.

Building the Long-Term Record

The true value of water level monitoring increases with time. A single year of data shows seasonal behaviour; a decade of data reveals long-term trends and aquifer response to drought; multiple decades provide the statistical basis for climate adaptation planning. Starting a monitoring programme — even a simple manual measurement schedule — immediately after commissioning is one of the highest-value investments a borehole owner can make.