Category Archives: Raeli Hydro Insights

Groundwater drawn from a well-constructed borehole is generally of good microbiological quality. However, the process of drilling, development, and installation inevitably introduces bacteria, organic material, and surface contamination into the borehole. Before any water is used for human consumption, the borehole must be thoroughly disinfected. Disinfection is not a substitute for good construction — it is a final safeguard that ensures the borehole is bacteriologically safe at the point of commissioning.

When Disinfection is Required

Disinfection is mandatory in the following circumstances:

• After initial construction — before any first use of the borehole.
• After any maintenance or repair work — whenever tools, pumps, or materials have been introduced into the borehole.
• After rehabilitation — following redevelopment or screen replacement.
• After a period of non-use — boreholes left idle for extended periods can develop bacterial populations.
• After suspected contamination — if a positive coliform test or other microbiological indicator is detected.

Disinfection Agent: Chlorine

Chlorine is the standard disinfection agent for boreholes, applied either as:

• Sodium hypochlorite (liquid bleach) — typically 5–12% available chlorine, widely available and easy to handle.
• Calcium hypochlorite (granular or tablet form) — typically 65–70% available chlorine, more concentrated and easier to store and transport.

The target is to achieve a free residual chlorine concentration of at least 50 mg/L (50 ppm) throughout the borehole water column, which is sufficient to kill the vast majority of waterborne pathogens including E. coli, Salmonella, and enteric viruses.

Step-by-Step Disinfection Procedure

Step 1: Calculate the Volume of Water in the Borehole

Determine the volume of standing water in the borehole using the casing diameter and the depth from the water table to the bottom of the casing. The formula is:

Volume (litres) = π × (radius in metres)² × water depth (metres) × 1000

Step 2: Calculate the Required Chlorine Dose

To achieve 50 ppm free chlorine, calculate the mass of active chlorine needed based on the water volume. Account for the concentration of the chlorine product being used.

For example: achieving 50 ppm in 500 litres requires 25 grams of active chlorine. If using 70% calcium hypochlorite, this equates to approximately 36 grams of product.

Step 3: Prepare and Introduce the Chlorine Solution

Dissolve the calculated quantity of chlorine in a bucket of clean water before introducing it into the borehole. Pour or pump the solution down the full depth of the borehole, ensuring distribution throughout the water column. Lower the solution along the borehole walls to treat the casing surfaces.

Step 4: Circulate and Agitate

Surge the borehole using the pump or a bailer to circulate the chlorinated water throughout the water column and into the gravel pack and screen zone. The chlorine solution must make contact with all surfaces.

Step 5: Contact Time

Allow the chlorine solution to remain in contact with the borehole for a minimum of 12 hours, and preferably 24 hours. Do not pump or use the borehole during this period.

Step 6: Flush the Borehole

After the contact period, pump the borehole to waste until the chlorine smell dissipates and a field test confirms residual chlorine has dropped to below 0.5 mg/L. Do not discharge the chlorinated water into watercourses or in quantities that could damage vegetation.

Step 7: Bacteriological Testing

Following flushing, collect a water sample for laboratory bacteriological analysis. The borehole should not be brought into service until test results confirm the absence of total coliforms and E. coli.

Special Considerations

In boreholes with confirmed iron or manganese bacteria (Gallionella or Leptothrix species), standard chlorine disinfection may need to be preceded by a shock treatment with higher concentrations. Biofouling of this type is resistant to normal doses.

Where a pump is installed, the pump and rising main must be removed or treated in situ to ensure all equipment surfaces are disinfected along with the borehole.

Documentation

A disinfection record should be maintained for every borehole, noting the date, chlorine product and dose used, contact time, flushing time, and the results of post-disinfection bacteriological testing. This record forms part of the borehole completion documentation and is essential for ongoing compliance and quality assurance.

 

 

 

When the drilling rig packs up and leaves a site, it takes with it the only opportunity to directly observe the subsurface. What remains is whatever was recorded during the drilling process. A thorough completion report and borehole log are the permanent record of that observation — the foundational documents for every decision that will be made about the borehole for the rest of its life. Their importance cannot be overstated, yet they are frequently neglected or poorly executed.

What is a Borehole Completion Report?

A borehole completion report is a comprehensive technical document prepared at the end of the drilling and construction process. It compiles all information gathered during site investigation, drilling, construction, development, and testing into a single permanent record. It serves as:

• A technical reference for the borehole owner and operator.
• A legal document for regulatory submission and licence compliance.
• A baseline dataset for future maintenance, rehabilitation, and monitoring.
• A contribution to regional groundwater knowledge.

National regulations in many countries require submission of borehole completion reports to the relevant water authority. Even where it is not legally mandated, producing a complete report is considered best practice.

Contents of a Completion Report

A well-structured borehole completion report should contain the following elements:

Project Information

• Client name and contact details
• Site location (coordinates, address, land parcel reference)
• Project purpose and intended use
• Drilling contractor name and licence number
• Supervising hydrogeologist or engineer

Site Description

• Surface elevation and topographic context
• Land use and potential contamination sources in the vicinity
• Access and site conditions at the time of drilling

Drilling Information

• Drilling method and rig type
• Drilling start and completion dates
• Total depth drilled
• Drilling fluid type and volumes used
• Bit sizes used at each stage

Borehole Construction Details

• Casing diameter, material, and depths
• Screen type, slot size, and installed depths
• Gravel pack specification and placement depths
• Grouting and sealing details
• Wellhead construction and protection measures

Formation Log (Lithological Log)

• Detailed description of rock or soil samples collected at regular intervals during drilling
• Formation tops and depths
• Notes on colour, texture, grain size, hardness, fracturing, and water strikes

Geophysical Logs (if conducted)

• Natural gamma, resistivity, caliper, or other downhole geophysical logs
• Interpreted formation boundaries and aquifer zones

Development Summary

• Methods used, duration, and observations
• Volume of water pumped to waste
• Turbidity measurements over time

Pumping Test Results

• Step drawdown test data and analysis
• Constant rate test data, drawdown curves, and recovery
• Recommended sustainable yield
• Transmissivity and storage coefficient estimates

Water Quality Results

• Physical parameters (colour, turbidity, odour)
• Chemical analysis results
• Bacteriological test results
• Any treatment recommendations

Disinfection Record

• Date, method, chlorine dose, contact time, and post-disinfection test results

The Lithological Log

The lithological (or geological) log is the heart of the borehole record. It is a graphical and written column showing the sequence of formations encountered from surface to total depth. Prepared by examining drill cuttings (chips of rock and soil brought to the surface by the drilling fluid) at regular intervals — typically every metre — it documents:

• Rock type and formation name (where known)
• Colour and weathering state
• Grain size and sorting (for sedimentary materials)
• Fracture frequency and orientation (for hard rock)
• Depth of water strikes and estimated yield at each strike
• Any drilling observations (rate of penetration changes, loss of circulation, colour changes in return water)

The lithological log is most accurate when cuttings are examined and described by a trained geologist on-site in real time. Post-drilling reconstruction from memory or incomplete notes produces unreliable records.

Borehole Construction Diagram

Alongside the lithological log, the completion report should include a scaled construction diagram showing the full depth of the borehole with all casing, screen, gravel pack, and grouting zones clearly indicated. This drawing is indispensable for future maintenance and rehabilitation work — knowing exactly where the screen is, how deep the pump can be set, and where grout seals are located saves time and prevents costly mistakes.

Filing and Archiving

Completion reports should be provided to the client in hard copy and digital format. Copies should be submitted to the relevant water authority and retained by the drilling contractor. Digital archiving in a georeferenced database greatly increases the long-term value of the data, allowing regional hydrogeological analysis as the dataset grows over time.

A completion report is only valuable if it can be found and used when needed. Proper filing and archiving is as important as the quality of the data it contains.

 

 

 

The difference between a borehole that lasts 30 years and one that fails in 10 often comes down to a single factor: whether it was on a routine maintenance schedule. Routine maintenance is the systematic, calendar-driven inspection and servicing of a borehole and its associated equipment, carried out at defined intervals regardless of whether a problem is apparent. It is preventive care, not reactive repair.

The Logic of Scheduled Maintenance

Reactive maintenance — fixing things when they break — is consistently more expensive than preventive maintenance. Emergency call-outs, expedited parts procurement, disruption to water supply, and the compounding damage that a failed component can cause to adjacent equipment all inflate the true cost of neglect. A well-designed maintenance schedule addresses the failure modes of each system component before they manifest.

The schedule must be realistic, documented, and assigned to specific responsible individuals. A maintenance plan that exists on paper but is never followed is no maintenance plan at all.

Weekly Tasks

Weekly checks are visual and observational, requiring no specialist skills. They should be carried out by the site operator or caretaker:

• Wellhead inspection: Check that the wellhead cap or cover is secure and undamaged. Look for signs of rodent activity, vandalism, or unauthorised access.
• Surface drainage: Confirm that the concrete apron is intact and that surface water is draining away from the wellhead. Ponding near the wellhead is a contamination risk.
• Pump operation: Confirm the pump is running normally — no unusual noise, vibration, or smell from the motor or control panel.
• Flow rate check: Note the discharge flow and compare to the expected rate. Any noticeable reduction should be logged.
• Electrical panel: Check indicator lights and circuit breakers. Log any fault alarms.

Monthly Tasks

Monthly maintenance involves slightly more detailed checks and simple measurements:

• Water level measurement: Measure the rest water level before the pump starts and the pumping level after a defined period of operation. Log both and compare to previous months.
• Amperage reading: Use a clamp meter to measure motor current draw. Rising amperage at the same output suggests increasing wear or changing pump efficiency.
• Discharge pipework: Inspect all visible pipework, fittings, and valves for leaks. Check the condition of the non-return valve if accessible.
• Chemical dosing equipment (where installed): Check dosing pump operation, chemical levels, and tubing condition.
• Log review: Review the week-by-week observations and note any trends or concerns for the quarterly check.

Quarterly Tasks

Quarterly checks introduce water quality sampling and more systematic performance assessment:

• Bacteriological water quality sample: Collect a sample in a sterile container and submit to an accredited laboratory. Results should be reviewed against drinking water standards.
• Physical water quality: Measure turbidity, colour, and odour on-site. Turbid or discoloured water should trigger a more detailed investigation.
• Pump performance test: Measure flow rate against drawdown and compare to the pump curve. Document any deviation from expected performance.
• Storage tank inspection (where present): Check tank integrity, inlet, outlet, and overflow; inspect and clean if necessary.
• Fence and site security: Inspect the site perimeter, access gate, and any warning signage.

Annual Tasks

Annual maintenance is a more thorough assessment that requires a qualified technician:

• Comprehensive water quality analysis: Full chemical suite including pH, electrical conductivity, hardness, major ions, nitrate, iron, manganese, and any site-specific contaminants of concern.
• Pump pull and inspection: Remove the submersible pump, rising main, and cable. Inspect the pump impellers, bearings, and motor casing. Check the cable for chafing or damage. Replace worn components.
• Borehole water level logger download: If a continuous logger is installed, download and review the full year of data. Identify trends, anomalies, and seasonal patterns.
• Chlorination: Following pump reinstallation, disinfect the borehole as standard procedure.
• Maintenance plan review: Review the schedule, update it based on observations from the year, and set the budget for the following year.

Five-Year Tasks

Every three to five years, the borehole itself — rather than just the equipment — should be inspected:

• CCTV downhole survey: A downhole camera survey inspects the condition of the casing, screen, and gravel pack. It identifies corrosion, joint displacement, screen blockage, or collapse that would not be apparent from surface observations.
• Redevelopment: Based on the CCTV findings and performance data, targeted redevelopment using surging, jetting, or air lifting may be appropriate to restore hydraulic efficiency.
• Full rehabilitation assessment: A hydrogeologist or well engineer should review all historical data and the CCTV footage to produce a structured condition report and rehabilitation recommendation.

Assigning Responsibility

Every task on the schedule must have a named responsible party, a target completion date, and a sign-off mechanism. For community or institutional boreholes, a formal operations and maintenance (O&M) committee with a dedicated budget significantly improves compliance with the schedule. Where specialist tasks exceed local capacity, a service contract with a qualified borehole maintenance company provides continuity and accountability.

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.