Manage landfill gas

You must manage the landfill gas produced by the waste in your site.

For landfills for non-hazardous and hazardous waste you must take measures to:

• collect landfill gas
• control the sub-surface migration of landfill gas through the sides of the landfill
• control the emission of landfill gas to atmosphere through the surface of the landfill

You must develop and maintain a landfill gas management plan.

You must design your landfill gas extraction and monitoring system based on your site-specific risk assessment.

Site phasing and waste placement

You must:

• design your site phasing plan to collect and minimise the emission of landfill gas
• minimise the size of the active tipping area, so that only the smallest possible area of waste is open
• minimise emissions from waste flanks – make sure the gradient is not too steep so you can install, maintain and replace effective capping and extraction systems

Treating and using landfill gas

You must use the landfill gas you collect to produce energy. If you cannot do this, you must either flare or use other methods to manage the gas.

Where your permit includes a gas utilisation plant, you are responsible for all monitoring and reporting associated with collecting, treating and minimising emissions and using the landfill gas. You are responsible for monitoring, collecting and minimising emissions from the landfill even if you sub-contract treatment and utilisation to a third party.

Your treatment system must have the capacity to deal with the volume of gas your landfill generates at different stages of the lifetime of the landfill.

When you design your gas utilisation plant you must consider the:

• composition of the raw gas extracted from the landfill
• need for and type of pre-treatment or conditioning you will apply to the gas before it is supplied to the combustion equipment
• type of combustion equipment you will use
• temperature of combustion
• set-up and maintenance of the combustion equipment
• fuel to air ratio applied during combustion
• use of secondary or quenched air
• potential post-combustion treatment of emissions and recirculation of exhaust

You must carry out dispersion modelling before you finalise your design and the location of the gas utilisation plant.

You must consider:

• the height of the flare and engine exhaust stacks
• appropriate retention times of the flare
• incorporating appropriate sampling ports

The optimal flare and engine exhaust stack height will depend on the:

• exit velocity
• pollutant loading
• flare retention time required – the indicative standard is 0.3 seconds at 1,000°C
• location of the stack in relation to receptors
• surrounding topography

You must consider the potentially corrosive compounds or components in the landfill gas when you select your plant and equipment.

You must remove potentially corrosive trace contaminants by cleaning the gas before combustion and the exhaust after combustion.

You must:

• meet the emission limit values in your permit for flare and engine emissions
• monitor emissions at least quarterly – use handheld electro-chemical equipment to adjust the engines to minimise emissions

Read guidance on:

• monitoring emissions from landfill gas engine
• monitoring emissions from landfill gas flares

Flaring

You must:

• have sufficient flaring capacity to treat all the gas when any gas utilisation plant is off line
• flare any excess gas above the capacity of the utilisation system

Other gas management options

Where landfill gas production rates fall and using the gas to generate energy is no longer viable, you must flare or use an alternative treatment or disposal technique. These include low calorific engines or flares and biological methane oxidation. This must be approved by the Environment Agency through a variation to your permit or an agreed change to your landfill gas management plan.

The Environment Agency’s low risk waste position ‘Burning landfill gas in a small appliance’ states that you do not need an environmental permit to burn landfill gas in an appliance with a net rated thermal input of less than 0.4 megawatts.

You must not use open diffusion type flares. They do not ensure consistent combustion and cannot be monitored.

Biological methane oxidation

Where your site is producing landfill gas but the methane concentration is too low to support a low calorific engine or flare, you must use biological methane oxidation.

Biological methane oxidation may be suitable:

• at sites significantly beyond the peak of their gassing life, where you cannot control gas migration using active forms of gas management
• in combination with other gas control methods
• at sites that accepted hazardous waste with very low rates of landfill gas production

You must consider:

• the permeability of the restoration soils
• the thickness and condition of the restoration soils
• the rate of landfill gas flux through the soil
• the presence or absence of cracks in the cover soils, or fractures in the site restoration
• biochemical factors such as nutrient availability, soil pH, temperature and moisture content
• whether you can use existing restoration soils, or whether you need to install a dedicated bio-oxidation system

Negligible landfill gas production

In exceptional circumstances landfill gas may only be produced in negligible amounts due to the nature of the deposited wastes or at the very end of gas production. Negligible landfill gas production means that active collection, extraction and treatment of the gas is unsustainable using active bio-oxidation techniques, low calorific utilisation or flaring. You must provide evidence of this to your local Environment Agency office, for example monitoring data from your site.

If the Environment Agency agrees that landfill gas production at your site is negligible, you do not need to collect landfill gas. However you should consider reducing any landfill gas emissions through passive bio-oxidation.

Operating your gas collection system

You must continuously monitor and adjust your collection system to:

• collect as much landfill gas as possible
• minimise air getting into the waste

You must include control levels for oxygen and nitrogen (balance gases) or free nitrogen at the wellhead. Concentrations of oxygen must not exceed 5% v/v (volume per volume) at the wellhead or in the collection pipework, unless you have justified site-specific reasons to exceed this.

Monitor carbon monoxide

You must routinely monitor carbon monoxide at well heads to identify waste fires or hot spots. Where carbon monoxide concentrations are higher than background concentrations for that cell, you must monitor the:

• temperature of the extracted gas at the well head
• temperature profile down the well

You must include details of how often you will monitor and assess above background concentrations for carbon monoxide in your gas management plan. You must give details of further investigations you will carry out if you exceed these assessment levels.

If you have not established the background concentration of carbon monoxide (for example in a new cell), use a carbon monoxide concentration of greater than 100ppm (parts per million) to trigger further investigation. Any carbon monoxide readings greater than 100ppm obtained using handheld instruments should be verified by laboratory analysis of a sample of landfill gas.

Inspect and maintain infrastructure

You must include a programme of inspection and maintenance of the infrastructure. You must inspect joints and fittings regularly to make sure they remain gas-tight. You must inspect for settlement as part of your routine site operations, especially where this may affect gas pipework.

You must maintain, repair or replace equipment to keep landfill gas collection efficient.

Assess the performance of the system

You must do a regular assessment of the efficiency of the gas collection system – include a programme of improvements if necessary. You must include any improvements you make or plan in your annual report or performance report. Your permit will tell you if and how often you need to send the Environment Agency a report.

Operational procedures for managing landfill gas

You must set out your operational procedures for managing landfill gas in your landfill gas management plan.

The procedures must refer to your conceptual site model to provide justification for the system as built.

System description

You must include a system description, including full as-built drawings, together with a record of all subsequent changes to the as-built design. This must include:

• location, specification and construction details of all collection wells, collection pipework, manifolds and valves
• details and process descriptions of gas extraction, utilisation, supplementary processing and flaring plant
• operational parameters for all elements of the gas control system
• a complete set of all commissioning measurement data
• operating instructions for each element of the gas management system
• commissioning into service and out of service procedures for each element of the gas management system
• a specification for routine operational monitoring for each element of the gas control system, including details of the parameters you will measure, the measurement precision required and the frequency of measurement
• a register of all infrastructure subject to routine adjustments, for example control valves
• a record of all incidents

Review your data

You must review the data from your gas extraction, utilisation, supplementary processing and flaring plant. Carry out a detailed appraisal of this data at least once a year. Compare the results with your conceptual site model, the objectives of your monitoring plan, and the parameters used in your GasSim model and air dispersion modelling.

You must investigate inconsistencies in the data. Where necessary, you will need to amend your landfill gas management plan to protect the environment and people’s health.

Monitoring, inspection and maintenance

Where you use automated control for monitoring, you must carry out periodic monitoring, inspection and maintenance. You must clearly identify these systems and procedures in your landfill gas management plan.

You must use the Environment Agency’s monitoring and certification scheme to monitor your flares and engines where appropriate.

Your monitoring, inspection and maintenance programme must include:

• who is responsible for monitoring, inspection and maintenance
• the frequency for monitoring, inspection and maintenance – daily, weekly or monthly
• how to document and report faults
• how to implement corrective actions
• a register of fault conditions and the corrective actions you took
• details of routine repairs and replacements
• review requirements for fault conditions and repairs
• an inventory of all replacement parts and contact details for relevant suppliers and manufacturers

You must only use competent personnel to operate and maintain your gas management system.

Accident management plan

As part of your accident management plan, you must have contingency measures for extracting landfill gas if the gas utilisation plant is unavailable. This includes having critical spare parts available on site and access to alternative temporary power supplies. Your plan must include timescales for fixing equipment.

The level and extent of your contingency measures must account for the sensitivity of nearby receptors to landfill gas migration and odour.