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.
