Landfill Gas Monitoring Procedures Methods and Guide

Landfill gas (LFG) monitoring procedures detect gas migration, identify uncontrolled emissions and check that gas collection and treatment systems are working. A useful monitoring plan covers methane, carbon dioxide, oxygen and relevant trace gases, using instruments and sampling methods suited to each task.

This guide explains monitoring wells and boreholes, surface surveys, building protection, equipment checks, interpretation and corrective action. Environmental compliance limits, workplace exposure limits and instrument alarm settings serve different purposes. Always identify the location, units, averaging period and applicable rule before comparing a result with a limit.

Technical and regulatory references checked: 15 October 2026. Environment Agency guidance below concerns England; requirements elsewhere in the UK must be checked with the relevant regulator. US examples identify specific federal provisions and do not replace state requirements or a site’s permit.

Key Takeaways

• Monitor migration, surface emissions, extraction performance and occupied spaces as separate but connected parts of the gas management plan.
• Do not wait for methane to reach its lower explosive limit before taking protective action.
• For Great Britain, EH40 workplace exposure limits for carbon dioxide are 5,000 ppm over eight hours and 15,000 ppm over 15 minutes. These are time-weighted limits, not general declarations that an atmosphere is safe.
• EA borehole benchmarks and US EPA methane requirements apply in specified environmental compliance contexts. They are not interchangeable with breathing-zone limits.
• Use the permit and applicable monitoring method to set frequencies, sampling procedures, reporting deadlines and responses.

Why Landfill Gas Monitoring Saves Lives and Protects Our Environment

Decomposing biodegradable waste generates gas that can move through waste, soil, fractured rock and buried services. Gas entering buildings, pits or chambers can create fire, explosion, toxic exposure and oxygen-deficiency hazards. The Loscoe landfill explosion illustrates why migration and building protection require serious attention.

• Detect migrating gas before it threatens people or property.
• Locate cover defects, leaking pipework and poorly controlled wells.
• Reduce methane emissions and support effective gas recovery.
• Provide evidence for permit compliance and review of the conceptual site model.

Migration distance depends on the source, pressure, geology, groundwater and available pathways. A liner or a single low borehole reading does not prove that nearby receptors are protected. Gas monitoring also does not replace groundwater or leachate monitoring or establish that a containment liner is intact.

Recovering gas for energy can improve the environmental performance of a landfill. However, gas generation, energy recovery and safety monitoring have different measurement objectives. Gas may remain hazardous after energy recovery is no longer commercially viable.

Essential Components of a Landfill Gas Monitoring System

Design the network around a conceptual site model: sources of gas, pathways through which it can move and receptors that could be affected. Review it when waste placement, extraction, capping, drainage or surrounding development changes.

Core Components of a Landfill Gas Monitoring System

• In-waste and extraction-well measurements for source characterisation and system operation.
• Perimeter and off-site ground-gas boreholes along relevant migration pathways.
• Surface surveys and, where required, quantitative methane flux measurements.
• Building, subfloor and service-duct monitoring and protection systems where risk assessment requires them.
• Measurements at headers, condensate systems, engines and flares appropriate to their functions.
• Meteorological observations, reliable records and clear escalation arrangements.

Assess gas release from leachate and condensate systems as part of the relevant operating and discharge arrangements. A discharge consent and a separate risk assessment may be needed; a gas monitoring result alone does not establish whether a sewer discharge is acceptable. Obtain assessment by qualified environmental engineers when designing or reviewing the network.

Gas Collection Wells and Probe Design

Extraction wells collect gas; monitoring boreholes measure conditions at selected locations. Their depths, screened intervals, seals and materials must suit the waste, geology, expected temperatures, leachate levels and settlement. There is no universally appropriate well depth expressed as a percentage of waste depth.

Prevent installations from connecting separate geological horizons or creating new migration pathways. Inspect wellheads, caps and seals for leakage, damage and settlement. Material selection must follow the engineering design rather than assuming that one plastic or metal is suitable for every location.

Perimeter Monitoring Stations

Ground-gas boreholes detect subsurface migration. Ambient-air stations assess air above ground; they cannot substitute for boreholes. Position and space monitoring points to intercept credible pathways towards receptors, rather than relying solely on equal spacing around a property boundary.

Keep locations identifiable, protected and accessible, and check whether water or damage has made a point unrepresentative. Supplementary equipment information is available in this landfill gas monitoring guide; use regulator-approved methods for compliance work.

Surface Emission Monitoring Points

Walkover surveys locate leaks around cracks, cover penetrations, wellheads and other features. Quantitative flux surveys measure methane emitted per unit area and time. A near-surface concentration in ppm and a flux in mg/m²/second describe different things and cannot be compared directly.

Use the route, probe position, instrument, background measurement and weather criteria specified by the applicable method. Do not apply a universal “below 5 mph and no recent rain” rule: weather restrictions must come from the actual monitoring protocol.

Building and Structure Monitoring Requirements

Assess occupied buildings, subfloors, service entries, chambers and other enclosed spaces within credible migration pathways. Depending on risk, protection may include barriers, ventilation, subslab systems, periodic testing and fixed detectors with audible and visual alarms.

Specify alarm levels through a competent risk assessment, allowing protective action before dangerous conditions arise. A regulatory structure limit is not automatically an appropriate alarm setting. Detector placement must account for the gas mixture, entry routes and airflow; do not assume that all landfill gas collects only at ceiling or floor level.

Inspect chambers remotely where possible. Entry into a confined space requires a suitable safe system of work and emergency arrangements; an ordinary gas survey is not an entry authorisation. See HSE confined spaces guidance.

Critical Gases to Monitor at Landfill Sites

Select gases and measurement ranges for the purpose of the survey. A percentage-range analyser used on raw landfill gas may not resolve low concentrations relevant to personal protection or surface-emission compliance.

Methane: The Primary Explosion Hazard

Methane is flammable in air at approximately 5–15% by volume under commonly quoted ambient conditions. This range is an illustration of the hazard, not an operating target: temperature, pressure, oxygen and other gases affect flammability. Gas above the upper limit can become flammable when mixed with air.

% by volume and % LEL are different scales. Using a methane LEL of 5% by volume, 100% LEL equals 5% methane; 25% LEL equals 1.25% methane; and 10% LEL equals 0.5% methane. Confirm the instrument’s methane calibration and LEL convention before converting its readings.

Infrared and catalytic sensors have different capabilities. Catalytic sensors need sufficient oxygen and can be poisoned or inhibited. A low reading from an unsuitable or over-range sensor cannot establish safety. The applicable environmental limits are set out in the regulatory section below.

Carbon Dioxide: Asphyxiation Risk Assessment

Carbon dioxide can displace oxygen and also has direct physiological effects. Measuring oxygen alone will not identify every dangerous CO₂ atmosphere. Its presence in a borehole can reflect landfill gas, natural soil processes or geological sources, so attribution requires background data and the site model.

The following HSE EH40 workplace exposure limits apply in Great Britain. They concern air breathed at work, not raw gas inside a well.

These averages are not instantaneous alarm settings or permission to enter an enclosed space. Control exposure under COSHH, including relevant mixed exposures. For CO₂, see also HSE’s explanation of carbon dioxide hazards.

Hydrogen Sulphide and VOCs: Health Impact Monitoring

Hydrogen sulphide is toxic. Smell is not a reliable warning: odour perception can be lost at dangerous concentrations. Use a suitable detector and the exposure limits above rather than attempting to judge safety by odour.

• Volatile organic compounds: the relevant substances depend on the waste and may include carcinogenic compounds.
• Non-methane organic compounds: a regulatory grouping, not a single substance with one universal health limit.
• Other trace contaminants: assess where the waste inventory or risk assessment identifies them.
• Siloxanes: relevant to gas treatment and engine performance as well as gas characterisation.

A photoionisation detector can screen for compounds detectable by its lamp, but it does not identify individual substances and is not a methane detector. Response varies by compound and calibration. Use appropriate sampling and laboratory analysis, such as gas chromatography/mass spectrometry, when compound-specific concentrations are needed.

Oxygen and Nitrogen: Indicators of Air Intrusion

Oxygen and nitrogen help identify air ingress and changing extraction conditions. Rising oxygen, changing gas balance, temperature and carbon monoxide may warrant investigation for air intrusion or heating. Apply the well’s operating limits and escalation procedure rather than assuming that “below 1–2% oxygen” is a universal regulatory standard.

Nitrogen can displace oxygen, and oxygen enrichment increases fire risk. Neither should be described as harmless in every context. Where an analyser reports a balance gas calculated by subtraction, label it as a calculated balance rather than a direct nitrogen measurement.

For England, the EA’s current gas management guidance says oxygen at the wellhead or in collection pipework must not exceed 5% by volume unless justified by site-specific reasons. This is an extraction-system operating criterion, not a breathing-air limit.

The same guidance requires routine wellhead carbon monoxide monitoring against the cell’s background. Where no background has been established, CO greater than 100 ppm triggers further investigation; handheld readings above 100 ppm should be verified by laboratory analysis. Investigate extracted-gas and down-well temperatures where CO rises above background. This process-investigation value is distinct from the EH40 CO exposure limits, even though one numerical value coincides.

Monitoring Equipment Selection Guide

Portable Gas Analysers vs. Fixed Systems

Portable analysers allow staff to sample many wells and boreholes. Check the available sensors, accuracy, resolution, operating range, water protection and suitability for low-oxygen samples. For potentially explosive atmospheres, select appropriately certified equipment.

Fixed systems can give continuous warning at selected receptors or process locations. Specify alarm response, power backup, fault indication and routine functional testing. A hybrid system may combine fixed protection at critical locations with portable surveys across the wider site. Neither approach eliminates the need to inspect monitoring-point integrity.

Calibration Requirements and Frequency

Follow the instrument manufacturer’s instructions, the monitoring method and permit requirements. Distinguish a functional or bump test, a calibration verification and an actual calibration adjustment. A successful bump test does not establish full measurement accuracy.

Use certified gases appropriate to each sensor and measurement range. Do not impose a universal monthly calibration cycle or use the same zero gas for every channel: nitrogen, for example, is not an oxygen-channel fresh-air span gas. Keep cylinder certificates, expiry information, instrument identification and records of results and adjustments.

Data Logging Capabilities

Record time, location, units, measurement range, instrument identity, weather and quality checks with each result. Retain original readings and an audit trail of corrections. GPS mapping and automated alerts can help identify spatial patterns, but require data review and clear responsibility for responding to alarms.

Where remote communications are used, provide local alarms and a response to power, sensor or communications failure. Loss of a signal must not be interpreted as a normal gas reading.

Weather-Resistant Features for Field Use

Choose protection against water, dust, impact and corrosion appropriate to the field conditions, together with sufficient operating temperature range and battery capacity for the planned survey. An IP rating describes ingress protection; it does not establish suitability for explosive atmospheres.

Cost-Benefit Analysis of Different Equipment Options

Obtain quotations for a defined specification and assess whole-life costs. Generic price bands can be misleading when sensor configurations and installation requirements differ. At gas-to-energy sites, reliable monitoring also supports stable gas supply and planned maintenance.

Step-by-Step Monitoring Procedures

Use a written, site-specific procedure. The following sequence is a framework to adapt to the approved method and risk assessment.

1. Pre-Monitoring Safety Checks

Review previous results, current alarms, site operations and access conditions. Check weather, communications, personal protection, hazardous-area equipment and emergency contacts. Identify traffic, unstable ground, open excavations and confined spaces before approaching a point.

Avoid confined-space entry where possible. Where entry is unavoidable, use the separately authorised safe system of work, atmospheric testing and rescue arrangements. Never improvise a rescue into an unknown atmosphere.

2. Equipment Calibration Verification

Check batteries, tubing, connections, filters, water traps and pump operation. Perform the required functional and calibration checks, allowing for instrument warm-up and ambient conditions. Record acceptance criteria and results. Withdraw an instrument that fails checks until it is restored and verified.

3. Sampling Technique for Subsurface Probes

1. Confirm the point identity, condition and relevant construction details.
2. Record atmospheric conditions and measure borehole pressure relative to atmosphere before venting or pumping disturbs it, using the sampling port and approved connection arrangement.
3. Check for blocked lines, flooded screens or damaged seals that could compromise the sample.
4. Apply the specified purge and sampling procedure. Select flow and duration for the installation volume, formation response and instrument; do not assume that one fixed flow or waiting time suits every borehole.
5. Record stabilised concentrations and any transient readings required by the method, with pressure, flow and observations where applicable.
6. Clear the sampling train as specified between points, avoiding exposure or ignition hazards from discharged sample gas. Close and secure the installation afterwards.

Do not routinely remove a cap and wait for pressure equalisation before taking the initial pressure measurement. Excessive pumping can draw in outside air or alter the gas being measured. Record any departure from the procedure and its likely effect on results.

4. Surface Emission Scan Methods

Map the prescribed route, establish background and verify calibration. Move slowly enough for the instrument’s response and sampling-line delay to locate emissions reliably; a generic walking speed is not a substitute for the method. Record leak locations and concentrations and arrange repairs and verification surveys.

As a specific US example, 40 CFR 60.765(c)–(d) specifies quarterly surveys, 30-metre traverses or established site-specific spacing, a probe inlet 5–10 cm above ground, and typical meteorological conditions. The method uses nominal 500 ppm methane-in-air calibration and calibration immediately before the survey. It is not a universal procedure for every landfill.

5. Documentation and Field Data Recording

Record date, time, technician, monitoring-point identifier, instrument and sensor details, gas units, pressure reference, calibration checks and weather. Include sample flow or purge information where required, water levels where relevant, and observations such as damaged seals, flooding or cover defects.

Record inaccessible points and invalid results explicitly. Preserve photographs, mapped exceedance locations, corrective actions and notifications. A missing reading is not evidence of compliance.

Regulatory Compliance Requirements

UK Standards for Landfill Gas Monitoring

The Environment Agency regulates environmental permitting in England. Wales, Scotland and Northern Ireland have their own environmental regulators and arrangements. HSE EH40 addresses workplace exposure in Great Britain; environmental permit compliance is a separate matter.

EA guidance LFTGN03, Table 8.2, gives off-site gas-monitoring-borehole trigger concentrations of 1% methane and 1.5% carbon dioxide by volume above agreed background concentrations. These are environmental migration benchmarks, subject to the permit and site assessment. “Above background” means the stated concentration increment, not a percentage increase relative to the background value. Earlier action levels should allow intervention before a compliance trigger is reached.

Do not use the historical explanatory footnote accompanying the CO₂ borehole figure as a statement of current occupational exposure limits. Use EH40 for workplace exposure and the actual permit for the compliance point.

The EA’s current monitoring guidance gives average methane flux standards for capped zones of 0.001 mg/m²/second for permanent caps and 0.1 mg/m²/second for temporary caps. Its approach combines locating and correcting defects with measuring flux through intact cap. These are flux standards, not ambient-air or breathing limits.

Maintain a gas management plan linked to the conceptual site model, extraction performance, monitoring results and corrective actions. Flare monitoring addresses combustion and emissions performance; it complements rather than replaces monitoring of gas within and around the landfill.

EPA Standards for Landfill Gas Monitoring

US federal requirements distinguish explosive-gas control under RCRA from collection-system and air-emission requirements under the Clean Air Act.

The surface standard measures collection-system performance; it is not a health-based exposure limit. At 500 ppm or more above background, the cited procedure requires a recorded exceedance and prescribed corrective action. Following those corrective provisions affects whether the monitored exceedance constitutes an operational violation.

Identify the Clean Air Act subpart, approved state or federal plan, and permit actually applicable to the site. Do not transfer operating parameters between different rules: oxygen, nitrogen and wellhead-temperature provisions can differ. Where other requirements also apply, assess them together.

State-Specific Monitoring Variations

State and local rules or permits may add monitoring locations, tighter limits, different methods or additional reporting. Confirm the actual provisions rather than assuming that a general statement about California, Texas or another state describes every landfill there.

Frequency Requirements Based on Site Classification

Increase surveillance where changing conditions or findings require it. Obtain any necessary approval before changing a mandatory frequency or monitoring point.

Data Interpretation and Action Levels

Understanding Normal vs. Abnormal Readings

The US EPA describes landfill gas as roughly half methane, with carbon dioxide and water vapour making up most of the remainder, plus smaller quantities of other gases. Actual composition varies with waste, decomposition stage, moisture and air ingress. This description is not a target for every well and has no meaning as a safe atmosphere for people.

Compare each point with its own baseline, relevant background and contemporaneous pressure and weather. Check unexpected results for sampling errors, flooded installations or instrument problems, while taking any immediately necessary protective action.

Methane Action Levels and Response Protocols

For every limit, document the gas, location, units, averaging basis, background adjustment, source of the requirement and response. Keep environmental compliance triggers separate from operational warnings and personal-protection alarms. A high raw-gas concentration in an extraction pipe and the same concentration in an occupied room demand very different interpretations.

Define who may investigate, who can adjust the system, who must be notified and who authorises return to normal operation. Do not delay evacuation or other protective action while attempting to confirm a reading.

Trend Analysis Techniques

Plot results against time, atmospheric pressure, rainfall, extraction settings and water levels. Map patterns across the network. Examine sustained changes, repeated exceedances and correlations with works or weather. Automated alerts and statistical tools help, but must not average away an important peak or conceal a permit exceedance.

Common Monitoring Challenges and Solutions

Weather Effects on Monitoring Results

Do not automatically increase extraction vacuum after rain or a raised gas reading. Excess extraction can draw air into the waste and contribute to heating. Investigate and make controlled adjustments under the operating procedure.

Equipment Malfunction Troubleshooting

Check for leaking connections, blocked filters, water in tubing, exhausted sensors, pump failure and over-range responses. Use manufacturer-approved checks and spare equipment where needed. Mark compromised results as invalid and assess whether earlier readings since the last successful check also require review.

Access Issues at Difficult Monitoring Points

Maintain paths, protective covers and point identification. Assess flooding, settlement, steep slopes, traffic and vegetation before sampling. Document missed points, the reason, temporary alternatives and remedial arrangements. Relocation must preserve the monitoring objective and receive any required approval.

Building Your Monitoring Schedule and Maintenance Plan

Creating an Annual Monitoring Calendar

List each monitoring task, required frequency, responsible person, equipment, reporting deadline and contingency. Include surveys after repairs, investigations after alarms, seasonal access work and review of the gas management plan. Allow time for poor weather and equipment failure without missing mandatory deadlines.

Equipment Maintenance Schedules

Base servicing, sensor replacement and calibration intervals on the manufacturer, method, condition and duty of the equipment. There is no universal requirement to replace sensors monthly. Keep maintenance records, spare consumables, valid calibration gases and a means of maintaining critical protection during servicing.

Staff Training Requirements

Train staff in landfill gas behaviour, measurement units, instrument limitations, sampling methods, data handling, alarms and escalation. Verify competence through supervised practice and field observations. Confined-space work, hazardous-area tasks and system adjustments require the specific competence and authorisation appropriate to those activities.

Taking Action When Gas Levels Exceed Limits

Emergency Response Procedures

For a suspected dangerous atmosphere, stop work, withdraw to a safe location, restrict access and activate the emergency plan. Notify the responsible site personnel and emergency services as appropriate. Do not operate ordinary electrical equipment in a potentially flammable atmosphere or enter an affected space to attempt ventilation or rescue.

Competent personnel should arrange suitable isolation, ventilation, investigation and clearance testing. Plan and practise these actions in advance, including loss of power or alarms outside normal working hours.

Regulatory Notification Requirements

Follow the site’s actual notification conditions. A generic allowance of 24–72 hours is inappropriate where immediate reporting is required.

For methane exceedances under 40 CFR 258.23(c), take immediate protective steps and notify the State Director. Record the levels and protective measures within seven days. Implement and record a remediation plan and notify the State Director within 60 days, subject to authorised alternative schedules.

For the surface-survey example in 60.765(c)(4), mark and record exceedances, correct and recheck within ten days, and follow the further ten-day and one-month checks as applicable. Three exceedances at one location in a quarter trigger collection-device installation within 120 days of the initial exceedance, unless an alternative remedy and timetable are approved. Consult the complete provision for the sequence.

Keep dated contact logs, notification copies and action records, including the applicable requirement and any regulator-approved variation.

Remediation Options and Implementation

Investigate the source and pathway before selecting a remedy. Options include repairing cover and seals, correcting condensate blockages, rebalancing or extending extraction, improving barriers or ventilation, and addressing service routes. Use competent engineering design and applicable approvals.

Verify the remedy through follow-up monitoring and assess effects elsewhere in the network. A lower reading at one point does not establish that migration has stopped or that a building is safe to reoccupy.

Frequently Asked Questions

How often should landfill gas monitoring be performed?

Use the permit and applicable rule. England’s schedule is site-specific; the cited US RCRA rule normally requires at least quarterly methane monitoring, while the cited US air rule requires quarterly surface surveys and specified follow-up. Critical receptors may require continuous warning. Closure does not automatically reduce the required frequency.

What are the most dangerous gases produced in landfills?

Methane creates fire and explosion hazards; carbon dioxide can cause harmful exposure and displace oxygen; hydrogen sulphide is toxic; and particular trace compounds can present acute or long-term health risks. Assess the mixture and the task. Smell, an oxygen reading alone or a methane-only detector cannot establish that every gas hazard is controlled.

Can landfill gas travel through soil into nearby buildings?

Yes. Permeable strata, fractures and service trenches can connect the landfill to buildings. Risk depends on the site model and building conditions rather than one universal separation distance. Barriers, subslab ventilation and detection systems must be designed, checked and maintained for the identified pathways.

What qualifications are needed to perform landfill gas monitoring?

• Demonstrated competence in the specific instrument and monitoring method.
• Understanding of gas hazards, measurement units and relevant permit requirements.
• Training in calibration checks, quality assurance, record keeping and response procedures.
• Additional competence for confined-space work or other specialist tasks where required.

Document training and supervised experience. A general environmental qualification alone does not establish competence for every gas-monitoring task.

How long must monitoring continue after a landfill closes?

There is no universal UK 30-year stopping point. Continue monitoring and management as required by the permit and applicable aftercare or surrender arrangements. Gas generation and migration risk can persist for decades. In England, the EA’s aftercare and permit surrender guidance requires site-specific evidence that the relevant completion criteria and risk requirements are met.

For US MSW landfill units, 40 CFR 258.61 specifies a 30-year post-closure care period that includes maintaining and operating the gas monitoring system. An approved State Director can shorten or extend that period under the rule. Completion of that period does not by itself resolve obligations under separate air rules.

Landfill gas flare monitoring is discussed in our dedicated article here.

Sources and Further Reading

• HSE EH40/2005 Workplace exposure limits, fourth edition, Table 1: carbon dioxide, hydrogen sulphide and carbon monoxide.
• HSE: General hazards of carbon dioxide.
• HSE: Confined spaces.
• Environment Agency: Management of landfill gas, LFTGN03, particularly Table 8.2 for borehole benchmarks.
• Environment Agency: Landfill operators—monitor and report your performance.
• Environment Agency: Manage landfill gas.
• Environment Agency: Aftercare and permit surrender.
• US EPA regulation: 40 CFR 258.23, Explosive gases control.
• US EPA regulation: 40 CFR 60.763, Operational standards.
• US EPA regulation: 40 CFR 60.765, Compliance provisions.
• US EPA regulation: 40 CFR 258.61, Post-closure care.
• US EPA: Frequent questions about landfill gas.

Originally published 24 November 2012; rewritten August 2025; safety figures, regulatory distinctions and monitoring procedures revised 15 October 2026.