Groundwater Monitoring Well Design, Construction and Development

Groundwater monitoring wells are the backbone of reliable data collection across mining, civil infrastructure and environmental projects in Australia. They provide continuous data on groundwater levels and quality, track contamination spread and support engineering decisions that carry real consequence. When bore construction is poor or well design ignores site conditions, the result is misleading groundwater quality and level data, increased risk of cross contamination between aquifers and potential non-compliance with approval conditions.

In Western Australia, all water bores must adhere to the Minimum Construction Requirements for Water Bores in Australia (MCR), published by the National Uniform Drillers Licensing Committee. Monitoring wells often require stricter specifications than supply bores because the purpose is measurement, not extraction. This article covers practical engineering design choices: location, depth, screened interval selection, correct materials, gravel pack, annular seals, well development and instrumentation.

Monitel is an engineering-led groundwater monitoring partner that designs and instruments groundwater monitoring wells and bores for long-term, automated data collection. For project-specific support, Monitel’s dedicated wells and bores service outlines how these solutions are delivered from design through to commissioning.

Groundwater Monitoring Objectives: Defining What the Well Must Measure

Well design always starts with hydrogeological objectives, not with a standard bore specification applied uniformly across every site. Monitoring methodologies must align with project objectives to ensure all parameters are measured appropriately.

Common objectives include:

• Baseline groundwater monitoring to establish pre-development conditions
• Compliance monitoring around mine pits, tailings storage facilities or discharge zones
• Tracking contaminant plumes at industrial or contaminated land sites
• Dewatering impact assessment along infrastructure corridors
• Supporting remediation efforts by tracking cleanup effectiveness

These objectives determine which aquifer or aquifers to screen, acceptable drawdown during sampling, whether water quality parameters such as dissolved oxygen, pH and electrical conductivity are required alongside groundwater levels, and whether automated telemetry is necessary. Groundwater monitoring requires both upgradient and downgradient wells to establish baseline conditions and detect contamination. Monitoring wells must be positioned along groundwater flow paths to measure quality accurately. They are essential for assessing risks to nearby water sources, and they help mining companies comply with environmental regulations.

Baseline data for monitoring must be collected over at least one hydrological year to establish natural seasonal variations. In Australia, contaminated land investigations typically align with the NEPM (2013) guidance and data quality objectives, which feed directly into monitoring well design. Monitel works with hydrogeologists to translate conceptual site models and DQOs into practical bore construction and instrumentation specifications.

Regulatory and Standards Context for Monitoring Wells in Western Australia

Regulatory expectations in WA combine national bore construction guidance, state approvals and project-specific conditions. Monitoring wells must meet legal and regulatory requirements across mining, infrastructure and environmental industries, and installation of monitoring bores requires regulatory approval in Australia.

Key frameworks include:

• MCR (4th edition, 2020): Sets minimum construction requirements for bore sealing, casing, screen placement and decommissioning. Groundwater monitoring bore installation must comply with MCR standards.
• ASC NEPM (2013): The Assessment of Site Contamination NEPM outlines groundwater monitoring requirements, emphasising defensible data, well construction logs and prevention of cross contamination between aquifers.
• DWER (WA): Compliance with the Western Australian Department of Water and Environmental Regulation guidelines is essential, particularly around mine dewatering, tailings storage and groundwater dependent ecosystems. State regulators issue compliance guidelines for groundwater monitoring that govern well locations, screened intervals and monitoring frequency.

Groundwater monitoring well design in Perth requires adherence to both state regulation and national standards, given the city relies heavily on the Gnangara and Jandakot mounds for groundwater supply. Urban groundwater monitoring in these areas often interacts with subsoil drainage and water-sensitive urban design, adding complexity to bore placement decisions.

Automated monitoring supports compliance with environmental approvals and reduces project delays by delivering continuous, audit-ready datasets. However, these frameworks shape minimum construction requirements but do not replace detailed site-specific design. Monitel helps clients interpret standards into practical monitoring solutions suited to their site conditions.

From Conceptual Site Model to Monitoring Well Network Design

The conceptual site model (CSM) is the bridge between hydrogeology and bore construction decisions. Hydrogeological understanding is crucial for designing effective groundwater monitoring systems, and every network design should be built on a defensible CSM.

Key CSM elements that affect well layout include:

• Stratigraphy, soil and rock types, existence of confined or perched aquifers
• Hydraulic conductivity, transmissivity and aquifer boundaries
• Groundwater flow directions and seasonal water level fluctuations
• Recharge and discharge zones, potential contaminant sources and receptors

Monitoring well network design then considers upgradient and downgradient locations, sentinel wells positioned towards receptors such as rivers, production bores or groundwater dependent ecosystems, nested wells to separate shallow and deep groundwater, and background reference locations outside the zone of influence.

Groundwater-dependent ecosystems must be protected through careful monitoring well placement, and monitoring bore placements should avoid unnecessary disturbance to wetlands and ecosystems. Preventing vertical cross-contamination between aquifer zones is critical when selecting well depths and sealing requirements.

Practical factors matter equally: long-term site access, power and telemetry coverage, traffic safety and the extent of protection needed against physical damage all influence where wells are positioned. Plan-view and cross-section diagrams drawn from the CSM are the most effective tools for communicating well spacing, depth and screened interval selection to drillers and regulators.

Determining Well Depth, Screened Intervals and Bore Construction Details

Depth and screen placement are the most critical design decisions for groundwater monitoring wells and groundwater monitoring bores. Wells must target specific aquifers ranging from shallow unconfined to deep confined systems. Screen intervals must capture representative water samples based on local geology.

Expected static water levels, aquifer thickness and vertical gradients drive decisions on total bore depth, length of the screened interval, whether discrete short screens or long composite screens are appropriate, and whether multilevel or nested wells are needed. Short screens provide better vertical resolution but require more installations. Long screens average out vertical gradients, which may mask important differences in groundwater quality between layers.

Screen slot size should match the formation’s grain size, typically retaining 40 to 60 percent of the formation material. Slot apertures generally range from 0.010 to 0.020 inches for sedimentary formations, with finer slots for silts and finer soils. This selection links directly to gravel pack design.

Monitoring well casings typically range from 2 to 6 inches in diameter (approximately 50 to 150 mm), with 50 to 100 mm being standard practice for non-pumped monitoring wells. Diameter must accommodate sampling methods, downhole pumps and water quality sensors. Bore construction details including stick-up versus flush mount, surface casing length and sump depth below the screen should be documented in a construction drawing and schedule before drilling begins.

Selecting Correct Materials: Casing, Screens and Gravel Pack

Material selection directly affects chemical resistance, data quality and service life. Materials must be chemically compatible with groundwater quality to prevent contamination of samples.

The material commonly used for bores is polyvinyl chloride (uPVC), with some projects utilising stainless steel (316 or duplex grades) for corrosive environments such as acidic mine drainage or high-salinity groundwater. Casing materials include PVC and stainless steel for durability, and the choice depends on the expected water chemistry and mechanical loads at depth. Carbon steel is generally unsuitable for groundwater quality monitoring because corrosion products bias dissolved metals results. Casing joints should not use lubricating oils or grease, as these can introduce contaminants to the monitored zone.

The well screen type should suit formation conditions. Wire-wrapped screens offer greater open area than machine-slotted casing and are preferred where higher flow rates or finer formations are involved.

The filter pack (or gravel pack) is placed around the screen to prevent fines migration while maintaining hydraulic connection with the formation. Filter packs are made of clean, graded sand to support the screen, typically consisting of washed, rounded silica grains sized relative to formation particle size distribution. The pack should extend from below the base of the screen to above the top of the screened interval, placed by tremie pipe to avoid bridging. Radial thickness of 50 to 100 mm between the screen and borehole wall is a common design target.

Monitel’s designs accommodate installation of pressure transducers, vibrating wire piezometers or multi-parameter water quality probes without damaging the screen or casing, ensuring that instrumentation fits within the selected bore diameter.

Annular Seals, Cross Contamination Control and Wellhead Protection

Preventing vertical leakage and cross contamination between aquifers is a core requirement of every monitoring well design. Annular seals prevent vertical leakage and contamination between aquifers by isolating the screened interval from overlying formations and the ground surface.

Bentonite is used to seal monitoring wells and prevent contamination. Bentonite chips or pellets are placed above the gravel pack, and bentonite seals should be placed unhydrated to a minimum thickness of 1 metre. In deeper bores, cement-bentonite grout may be placed via tremie pipe above the bentonite seal to fill the annulus to the surface. Seal placement method, hydration time and volume verification are important to meet minimum construction requirements and prevent short-circuiting of water flow between zones.

Surface casing and sanitary seals protect against surface contamination, spills and physical damage. Standard practice in WA includes a concrete pad sloped away from the casing, with the bore protruding above ground level. Bores should be secured with designs preventing damage and unauthorized access, typically using lockable steel monuments, bollards in mine haul roads or trafficable flush-mount covers in paved areas. Corrosion-resistant covers are used in coastal or saline environments.

As-built construction records must document seal materials, depths and volumes to demonstrate compliance and support data defensibility over the life of the bore.

Drilling Methods for Monitoring Wells and Their Design Implications

The drilling method is a design variable that affects borehole stability, sample disturbance and achievable depth. Common drilling methods for groundwater monitoring bores in Australia include:

• Hollow-stem auger: Suitable for shallow, unconsolidated soils. Fast but may smear borehole walls.
• Rotary mud: Used for deeper or mixed formations where borehole stability is a concern. Requires management of drilling fluids to avoid clogging the formation.
• Air-rotary and down-hole hammer: Effective in hard rock. Useful for locating fractures in consolidated formations.
• Sonic drilling: Provides high-quality cores with minimal disturbance, preferred for contaminated sites or where detailed stratigraphic logging is critical.

Monitoring wells should be drilled as close to vertical as possible, generally maintaining deviation within 1 to 2 degrees per 20 metres. Each method influences borehole diameter control, wall disturbance and the risk of smearing contamination along the borehole.

Drilling fluids must be selected and managed carefully to avoid introducing contaminants or altering groundwater chemistry in the monitoring interval. The drilling specification should include lithological logging, depth to water observations and recording of water strikes to allow screen placement to be refined on site as conditions are confirmed.

Construction Process: Step-by-Step Monitoring Well Installation

Even a well-designed monitoring well can underperform if construction steps are not followed precisely. The well installation process follows a logical sequence:

1. Set out and survey the bore location, establishing elevation in mAHD.
2. Drill the pilot hole and log lithology continuously.
3. Ream to final borehole diameter if required.
4. Install casing and screen (pre-packed or standard) with centralisers. Centralisers help maintain alignment of well screens during installation and ensure even gravel pack distribution.
5. Place gravel pack to design depth by tremie pipe. Filter packs of clean sand support the well screen and maintain aquifer integrity.
6. Install annular seals above the gravel pack, confirming depths with volume calculations.
7. Construct surface casing, concrete pad and headworks.
8. Survey the top of casing (TOC) elevation for reference.
9. Complete as-built records documenting all construction details.

Confirming pack and seal depths through careful volume checks prevents voids and bridging. Monitel integrates installation details such as casing schedule, screen depths and TOC elevation directly into the monitoring database, ensuring accurate depth to water and mAHD calculations from the first measurement.

Well Development: Achieving Representative Groundwater Quality and Levels

Well development is often rushed, yet it is critical for producing representative groundwater data and ensuring long-term bore performance. Monitoring bores must be developed to remove fines for accurate sampling.

The purpose of development is to remove drilling fluids, fines and disturbed formation material from the gravel pack and screen, reduce turbidity and restore natural hydraulic conditions around the bore. A bore that is not properly developed will produce samples influenced by drilling artefacts rather than true formation water.

Common development techniques include:

• Surging with a surge block or bailer to mobilise fines
• Air-lifting for moderate to high yield bores
• Pumping with inertial pumps (e.g. Waterra) or submersible pumps
• Low-flow purging where minimal disturbance is required

Development end-points are defined by stabilisation of field parameters: pH, electrical conductivity, dissolved oxygen, temperature and turbidity measured across consecutive purge volumes. Many sampling plans set turbidity targets below 5 NTU. Proper development reduces long-term maintenance, minimises well silting and enables more accurate dissolved oxygen and groundwater quality measurements during routine monitoring.

Instrumenting Monitoring Wells: Levels, Water Quality and Automation

The value of a monitoring well is realised when it is correctly instrumented and producing reliable data. Groundwater monitoring relies on automation to enhance data integrity and reduce labour costs, particularly on remote or large-scale projects.

Common instrumentation includes:

Automated groundwater monitoring systems combine sensors, data loggers, telemetry and cloud platforms to provide real-time groundwater level and water quality data, alarms and reporting. Design considerations include dedicated tubing for pumps, separate ports for level sensors, non-contaminating cables and sufficient casing diameter for future instrumentation upgrades.

Monitel selects instrumentation compatible with well construction materials, expected water chemistry and project data quality requirements, ensuring environmental compliance throughout the monitoring programme.

Common Design and Construction Pitfalls to Avoid

Most monitoring well failures stem from predictable, avoidable errors rather than unforeseen conditions. Key pitfalls include:

• Screens installed in the wrong stratigraphic interval or spanning multiple units unintentionally
• Excessive screen length that averages out vertical gradients and masks contamination
• Undersized or poorly graded gravel pack causing fines ingress or poor hydraulic contact
• Incomplete annular seals allowing cross contamination between aquifer zones
• Casing or screen materials that react with groundwater, biasing dissolved metals and other quality results
• Inadequate well development leaving turbidity persistently high and compromising sampling accuracy

The consequences are significant: unreliable groundwater level data, biased water quality results, non-compliance with monitoring conditions and costly re-drilling. Robust design reviews, construction supervision and as-built validation are essential steps on high-risk mining and infrastructure projects. Careful planning at the design stage prevents most of these issues.

Monitel’s Approach and When to Seek Specialist Input

Monitel operates as an engineering partner, helping project teams design, instrument and operate groundwater monitoring wells and bores that produce defensible, audit-ready data suited to each site’s risk profile.

Typical involvement includes:

• Collaborating with hydrogeologists on monitoring well design and network layout
• Preparing bore construction specifications covering drilling methods, materials and minimum construction requirements
• Designing sensor and telemetry configurations for automated data acquisition
• Establishing cloud-based reporting systems that support ensuring environmental compliance

Specialist input is particularly valuable for complex stratigraphy, nested well installations, tailings storage facilities, high-salinity environments and projects with strict environmental approval conditions. Getting the design right from the outset avoids costly re-drilling and ensures the monitoring network delivers representative groundwater data throughout the project lifecycle.

Contact Monitel to discuss your upcoming groundwater monitoring well or bore installation and develop a monitoring solution tailored to your site conditions.