What to include in your hydrogeological risk assessment

This section will help you develop your application for a permit for a landfill or to deposit waste on land as a recovery operation. It will help you decide what information you must include in your application.

Use this guide with the application forms and risk assessment guidance.

Where your conceptual site model confirms you require one, this guide will help you develop your hydrogeological risk assessment. You must complete it in addition to the conceptual site model and the environmental setting and installation design (ESID) or environmental setting and site design (ESSD) reports.

When you complete your hydrogeological risk assessment you must:

  • refer to all of the sections suitable for the tier of assessment – if any are not relevant you must include the reasons
  • include all relevant information in tables within the text of the report at the appropriate point
  • include all relevant information you used to complete the report in the appendices, or provide references if they are within the ESID report or ESSD report
  • include all numerical and analytical models you refer to in the report, including their results, in electronic format
  • include drawings and cross-sections, where applicable and use an appropriate scale (such as 1:1250) to show the relevant details – one drawing can provide information for more than one part
  • include, where applicable, time series data in graphical plot format, for leachate, groundwater and surface water level and quality

The following information may help you prepare your permit application:

Your hydrogeological risk assessment must include the following sections.

Introduction

Your introduction to the report must include:

  • details of the proposed operator, site name and address
  • details of the agent who completed the risk assessment
  • report context – include background information and an outline of the installation or site
  • site setting, including an outline of the proposed installation or site and how it relates to historically operated areas of landfill or waste recovery activities
  • the conceptual site model or a reference to the report it is in – include the waste acceptance criteria that will be applied if appropriate

Hydrogeological risk assessment

If your conceptual site model confirms that your site presents a potential risk to water, you must carry out a hydrogeological risk assessment.

Nature of the hydrogeological risk assessment

You can use a tiered approach to do your hydrogeological risk assessment. This means that the greater the risk of groundwater pollution, the more complex the assessment you carry out. Read the guide for how to carry out risk assessments for your environmental permit.

You must do an appropriate risk assessment to determine the risk your site poses. This must justify the risk assessment method you use. For example, the level of assessment required for a landfill for inert waste or waste recovery operation may not be the same as that required for a landfill for non-hazardous waste.

You must consider the:

  • potential risks presented by the site
  • sensitivity of the surrounding water environment
  • hazards posed and the likelihood of the risk happening

Proposed assessment scenarios

Your hydrogeological risk assessment report must cover the whole lifecycle of your site from when operations begin until the permit is surrendered.

Your report must include:

  • all reasonably foreseeable scenarios, to assess the risks to the water environment at different stages of the site’s lifecycle – include likely external influences, for example climate change, failure scenarios and accidents for each stage
  • how you decided on the different lifecycle stages and how certain inputs may change with time, such as the degradation of the containment, including the capping, or leachate drainage systems
  • all reasonably foreseeable scenarios for further quantitative assessment, for example how the engineered lining systems will degrade
  • the impact of long-term changes in groundwater level, particularly where groundwater is pumped to reduce natural levels - you must account for seasonal variations and likely changes in rainfall pattern caused by climate change
  • the proposed technical precautions in conjunction with any natural geological barriers or attenuating layer

To increase leachate levels at your site read manage leachate

Priority substances

You must identify and justify the priority substances you will model that are likely to be in your leachate. These must represent actual leachate, or surrogate substances that you will use as indicators through risk screening. Read the section on leachate characterisation. You must include:

  • the actual and potential presence of hazardous substances and non-hazardous pollutants in the waste or leachate
  • an assessment of the substances’ chemical and physical characteristics
  • an assessment of any uncertainties, such as changes in waste types, associated with the choice of representative or surrogate substances

Review technical precautions: what you must include

You must review your technical precautions.

Landfills for hazardous or non-hazardous waste

You must detail the steps you will take to prevent hazardous substances and limit non-hazardous pollutants in the leachate from entering groundwater.

You must include an assessment of:

  • the capping design, including infiltration rates
  • the lining design and how it will detect leaks
  • the leachate drainage and recirculation systems
  • leachate level control
  • groundwater and surface water management and monitoring systems

Leachate level

You must include a water balance calculation to predict the volume of leachate the site will produce over time. This must include the:

  • volume of leachate your site currently generates (if appropriate)
  • potential future volumes, based on water balance calculations
  • volumes of leachate that may be stored on site within the cells (the volume below the existing or proposed compliance limits)

You must include details of the proposed leachate levels above the base of each landfill cell and how you will monitor these. Read monitor and report your performance.

Leachate characterisation

You must characterise leachate quality for all levels of risk assessment. Where possible, you must use data from representative samples of leachate from either:

  • the landfill
  • sites that take similar wastes

You should assess the leachate chemistry to predict its potential hazard to both:

Leachate characterisation: no existing leachate information is available

Where you do not have data, you can predict likely leachate chemistry from:

  • a data review of similar landfills that you own
  • information on landfills that take similar waste streams operated by a third party - this information is available from the Environment Agency’s public register

Where you rely on information gathered from other sources, you must quality assure it. You must:

  • obtain information about waste streams and potential leachate quality
  • review data usability (completeness, comparability, representative, precision, accuracy)
  • review the data and identify substances of concern
  • determine the source term

You must use leachate quality information from landfills permitted under the Landfill Directive.

Screening landfill leachates: landfills for hazardous or non-hazardous waste

Use the landfill leachate analytical framework to identify the highest risk substances likely to be in the leachate.

The framework summarises the information you need to tell laboratories, so they know what tests to use.

You must include details of leachate, groundwater and surface water monitoring.

You must assess the design of your leachate management system to make sure the measures you propose provide sufficient control. For example, will it provide the level of control you assumed in the hydrogeological risk assessment. This must be for as long as your risk assessment predicts them to be necessary.

Landfills for inert waste and waste recovery operations

You must include details of the technical precautions you will put in place to protect groundwater.

You must, where applicable, include a review of the:

  • natural geology
  • artificially enhanced geological barrier
  • attenuation layer
  • surface water management systems

Leachate characterisation: soils and other inert waste

The Environment Agency do not normally require you to sample leachate at landfills for inert waste. Data is unlikely to be available. For soils and other inert waste, you can carry out leaching tests. You must use the methods in the Council Decision annex, Section 3.

You must be careful when you interpret leaching test results. Most waste materials are heterogeneous. You must consider how the leaching test results relate to actual site conditions.

You must identify and explain how you have chosen the substances you will test for. That will depend on the properties of the wastes you will deposit.

Where your risk assessment suggests a potential threat to groundwater or surface water you must include details of how you will monitor them.

To understand the environmental permitting requirements and how to comply with your permit, read either:

Risk assessment level

Your conceptual site model, site investigation and leachate screening will help you decide the complexity of your risk assessment.

If your conceptual site model confirms that your site presents a potential risk to water, you must carry out a hydrogeological risk assessment.

Your risk assessment must provide confidence in the predicted impacts.

You must consider both the level of uncertainty and likelihood of an impact.

Your risk assessment must:

Find out what tools you should use to complete and submit your risk assessment.

Where you plan to accept non-hazardous or hazardous waste below the water table at your landfill or deposit for recovery operation and you will manage leachate, you can assess the risk using the contaminant fluxes from hydraulic containment spreadsheet.

Where you plan to accept inert waste at your landfill or deposit for recovery operation below the water table, read depositing inert waste into water.

When you’ll need to do a generic or detailed quantitative risk assessment

Read plan the environmental setting of your site.

You can normally carry out a generic quantitative risk assessment (GQRA) where the risk posed by your site is low and it is not in a sensitive location.

Read generic quantitative risk assessment (GQRA)

You must normally carry out a detailed quantitative risk assessment (DQRA) for landfills that will accept hazardous or non-hazardous waste.

Read detailed quantitative risk assessment (DQRA).

Pollutant calculations

Your permit application must show that you’ve taken appropriate measures to both prevent the direct discharge of hazardous substances and limit the discharge of non-hazardous pollutants to groundwater.

You must support your application with calculations. These will depend on the environmental setting of your site and your development proposals.

Examples of calculations include the:

  • travel time for leachate to migrate through any lining systems and attenuation layer to a receptor (normally groundwater but possibly a surface water receptor)
  • predicted concentrations of contaminants at appropriate monitoring points in the subsurface (to derive relevant control levels)
  • potential attenuation of contaminants within the lining systems and attenuation layer, for example the retardation of compounds due to sorption - you must provide evidence that these processes are likely
  • predicted decline in the concentration of contaminants in leachate over time
  • predicted degradation of any artificial components of the liner and other engineered systems
  • proposed completion criteria for leachate quality given the long-term attenuation capacity of any mineral layer
  • predicted time when you will cease active management of the landfill (for example, extraction of leachate and maintenance of leachate collection systems)

Read the groundwater risk assessment guide for more information on probabilistic calculations.

Justify your modelling approach and software

Where your risk assessment requires a quantitative modelling approach, you must justify the:

  • selection and suitability of your model to represent all the scenarios, such as the different modelled phases of the lifecycle and potential impact of accidents and hydrogeological conditions
  • confidence levels used within any stochastic modelling
  • use of a particular computer model or software (including the version number), which includes reference to how you translated the conceptual site model into the mathematical model, and any simplifications you made
  • suitability of the model to identify and represent receptors and compliance criteria

Model parameterisation

Your report must include the:

  • nature of the parameterisation process including all model inputs, probability density functions and model calibration, where appropriate
  • prioritisation of site-specific data against model defaults and a justification for all input values, including all uncertainties used within the model

Sensitivity analysis

You must include a sensitivity analysis within your risk assessment report. You must:

  • justify the sensitivity analysis you carried out to simulate different justifiable ranges of input parameter values such as the impact of climate change – where appropriate, this should include the use of probabilistic model runs
  • consider the assessment limitations, the assessment of uncertainties and the need for safety factors

Model validation

You must:

  • compare the modelled output against what is observed in the field and is represented within the conceptual site model – for example, the hydraulic gradients must be compatible with permeability, the modelled leachate heads above the basal liner must be compatible with those observed
  • justify why the model provides a realistic representation of reality
  • provide an explanation of any limitations in the modelling, such as any warning messages that are present within a Landsim model

Accidents and their consequences

Your application must consider the degradation of engineered systems in your risk assessment. This is to predict the risk of pollution throughout the site’s life. It will assess the long-term flux of pollutants discharged from your site.

You must include a qualitative assessment of:

  • the impact of accidents and resulting damage to liner systems, leachate management and other engineering and management structures
  • the likelihood of the accidents occurring and their consequences
  • whether the accidents you have specified require quantitative assessment and, if so, include this
  • any additional scenarios that you consider need further quantitative analysis and the implications for modelling, for example extreme weather events

Examples of accidents or failures scenarios

Accident or failure scenario Direct consequence of an accident or failure scenario
Fire, vehicle accident, machine driver error Damage to geomembrane basal or sidewall liner
Fire, structural failure, machine driver error, subsidence, flooding Destruction or degradation of leachate management system
Drilling, penetration of waste Perforation of artificial sealing liner or artificially established geological barrier (or both)
Stability failure, unforeseeable pore water pressure, subsidence, landslides Failure of side wall lining system
Drilling, stability failure, subsidence, void migration, landslides, sub-grade failure Failure of artificial sealing liner or artificially established geological barrier (or both)
Waste slippage, vehicle accident Failure of artificial sealing liner or artificially established geological barrier (or both), waste or leachate outside contained area (or both)
Hydrostatic uplift due to failure of groundwater management system Failure of artificial sealing liner or artificially established geological barrier (or both)
Increase in leachate level due to failure of leachate extraction infrastructure Leachate level greater than that modelled - unacceptable discharge of hazardous/non-hazardous substances, leachate outside contained area (or both),

Emissions to groundwater or surface water

You must establish through your hydrogeological risk assessment whether the predicted direct or indirect input of hazardous substances or non-hazardous pollutants to groundwater and surface water will be acceptable. You must include all the scenarios you considered, including the different modelled phases of the site’s lifecycle and the potential impact of accidents or failures.

You must set Environmental Assessment Levels to make sure you will meet the relevant environmental standards at each compliance point.

You must use appropriate water quality standards and site-specific natural background groundwater quality to derive appropriate Environmental Assessment Levels for each compliance point.

Hazardous substances

For each of the scenarios you considered, your hydrogeological risk assessment must demonstrate what you will do to prevent hazardous substances entering groundwater.

You can consider the input of hazardous substances to be prevented if there are no attributable, discernible concentrations of hazardous substances in the groundwater. You must include a summary of what the concentrations are and justify your conclusions.

Non-hazardous pollutants

You must include, for all the scenarios you considered, an assessment of whether:

  • the predicted concentrations of non-hazardous pollutants exceed the relevant Environmental Assessment Levels or other environmental quality criteria at the down hydraulic gradient compliance point
  • you have sufficiently limited the introduction of non-hazardous pollutants to groundwater to avoid pollution – summarise this in a statement and fully justify your conclusions

For each of the scenarios you considered, your hydrogeological risk assessment must demonstrate that your precautions will limit the input of non-hazardous pollutants to groundwater.

If you choose a compliance point other than adjacent to the site, you must both:

  • justify that in your application
  • refer to the sensitivity of the site’s location

Groundwater compliance points

For predictive modelling of hazardous substances, you must normally set your compliance point immediately down hydraulic gradient of the discharge. This must be:

  • just below the water table
  • adjacent to the discharge area
  • within the expected vertical mixing depth

For a landfill site, compliance limits are included in your environmental permit. The Landfill Directive calls these trigger levels. A deposit for recovery permit may also include compliance limits if the Environment Agency consider them necessary. Compliance limits are set at a compliance point. This is to check that the control measures you have put in place work. It confirms that your site is not having an impact on groundwater. The compliance limit is determined through the risk assessment process and you must include it in your report.

The Environment Agency will normally assess compliance with emission limits for hazardous substances at monitoring points. These are normally one or more boreholes next to the site in the groundwater out flow region (down hydraulic gradient). The location of these accepts the practical problems in collecting samples from beneath a site.

The Environment Agency will normally assess compliance with emission limits for non-hazardous pollutants at the same boreholes. They may agree boreholes further away from the site where the groundwater has no current or potential future resource value.

Where you want to place a compliance point other than next to the site, you must explain why in your application.

You must normally monitor the groundwater level and concentrations of potential pollutants in the groundwater. Read monitor and report your performance.

Surface water as a compliance point

You can assign the compliance point for non-hazardous pollutants at local surface water down gradient of the site where either;

  • your risk assessment shows that your site will have no impact on groundwater
  • you do not consider that groundwater is a resource for future use

The Environment Agency will normally only accept surface water as a compliance point where:

  • you have considered all the source, pathway and receptor linkages
  • you have identified surface water as a high priority risk
  • they agree that it represents the most significant (water) receptor for any contamination from the site

Read surface water pollution risk assessment for your environmental permit.

You must normally monitor the concentrations of potential pollutants in surface water in any water body that is at risk from your site. Read monitor and report your performance.

Groundwater control levels

Groundwater control levels are a numerical value below the compliance limit. You should use them as an early warning to investigate the cause of increasing concentrations or carry out corrective action. Read monitor and report your performance.

Control levels must:

  • identify adverse trends that suggest a potential impact on groundwater by leachate
  • allow for variation in water quality from baseline conditions
  • give sufficient time to take corrective or remedial action before you exceed a compliance limit

You must use groundwater control levels to:

  • determine whether a landfill is performing as designed
  • draw the attention of site management to adverse trends in the monitoring data

If your site exceeds a groundwater control level that suggests it may not be performing as you predicted. You must take necessary measures to prevent the breach of a compliance limit.

What to do if your risk assessment fails

If your risk assessment fails to provide confidence that your site will not pollute groundwater, you can:

  • collect additional site-specific data (such as attenuation properties or groundwater levels and quality) to reduce uncertainty – this will normally allow you to use better assumptions in your risk assessment
  • carry out a higher tier of risk assessment with greater level of complexity – this will only apply where you have carried out a qualitative assessment or generic quantitative risk assessment
  • alter the nature of the development so that it presents less hazard or risk to the groundwater environment - this could include for example, altering the proposed waste you will deposit, relocating the facility to a less sensitive environment or upgrading the engineering
  • identify alternative waste management options

Surface water management

Your application must include how you will manage surface water to prevent ingress to the site or flooding. You must provide a surface water and water balance assessment for both your operation and the site as a whole.

Monitoring

You must monitor, where applicable:

This is to confirm the assumptions you have made in your groundwater risk assessment. Read monitor and report your performance.

Your risk assessment must include:

  • details of your monitoring scheme, including a plan of the location of each monitoring point
  • the rationale for the design of your monitoring programme

Once you start depositing waste at a landfill for hazardous or non-hazardous waste, you must monitor the leachate level and quality. You must compare the results of that monitoring with your original risk assessment predictions. You must review your original risk assessment against actual leachate and groundwater monitoring data annually.

Where your permit requires you to review your hydrogeological risk assessment, you must do this every 6 years.

Where you want to vary your permit to change the monitoring conditions or compliance limits, you must provide evidence from existing monitoring data to support your application.

Read guidance on monitoring of landfill leachate, groundwater and surface water for information on monitoring programmes.

Hydrogeological leachate completion criteria

Your hydrogeological risk assessment will determine whether the activity is likely or unlikely to cause pollution. Your assessment of hydrogeological risk must include the whole lifecycle of the site. It must determine when your site will achieve the hydrogeological leachate completion criteria. This will form part of your environmental permit surrender application.

You have achieved the hydrogeological leachate completion criteria when both:

You must include details of the pollution potential of the leachate and when this will not pose an unacceptable pollution risk

Conclusions

Your hydrogeological risk assessment report must include specific conclusions to:

Tables

Tables to summarise information and data.

You must:

  • use tables where applicable
  • put tables next to the text they relate to

The tables in your hydrogeological risk assessment must normally include:

  • reference to any prior site or ground investigations
  • the proposed conceptual site model – including a summary of all the relevant source, pathway and receptor terms and schematic, annotated cross-sections
  • the proposed assessment scenarios, including the lifecycle phases and possible accidents, and how you chose these scenarios – such as how certain inputs may change with time
  • the justification for the priority contaminants to be modelled
  • the derivation and justification of the input parameters
  • the model validation exercise, which compares the output against observed site conditions
  • the modelling results and the presentation of potential resultant concentrations of hazardous substances and non-hazardous pollutants at the relevant compliance points
  • the results of any sensitivity analysis
  • the essential and technical precautions that must be used to prevent an unacceptable discharge
  • the hydrogeological completion criteria
  • the monitoring scheme, including proposals for the monitoring of leachate, groundwater and surface water
  • the proposed assessment levels and compliance limits for hazardous substances and non-hazardous pollutants

Drawings

The drawings in your hydrogeological risk assessment will be site-specific.

You must label each drawing with the:

  • drawing title
  • site name
  • name and address of the operator
  • date the drawing was made
  • drawing identification number
  • scale of the drawing
  • key
  • grid lines and north point
  • paper size of the original drawing

You must include identification numbers for each monitoring point.

Your hydrogeological risk assessment must include, where applicable:

  • a plan and cross-sections which show all potential receptors of emissions to ground and surface water, including compliance points, potential pathways, the geology and hydraulic gradient
  • annotated schematic cross-sections for each scenario, including the different phases and engineering design of the site’s lifecycle – include any vertical or horizontal scale exaggeration or modification
  • annotated schematic cross-sections or plans of the different scenarios you considered, showing the potential concentrations of hazardous substances and non-hazardous pollutants at the relevant compliance points
  • a plan of all monitoring points for leachate, groundwater and surface water, indicating all points where assessment limits and compliance limits will be set – you can annotate relevant limits on your plan
  • a plan showing the geology, groundwater contours and hydraulic gradient, based on site-specific groundwater level monitoring – include any seasonal variations

Appendices

Include appendices in your hydrogeological risk assessment. You do not need to include information in the appendices if you have included it within the main text of the report.

You must normally include:

  • ground investigation information
  • electronic copies of all models and results you relied on in the assessment
  • hard and electronic copies of any data you used including any time series plots presented
  • results of any sensitivity analysis you carried out for the site
  • how you derived the hydrogeological completion criteria
  • the proposed risk-based monitoring plan for the site
  • how you derived the leachate, ground and surface water assessment levels and compliance limits

Landfill leachate analytical framework

Volatiles

Basis of test: Purge and trap or headspace gas chromatography mass spectrometry (GCMS), full scan EI mode (for example, EPA 8260)

Mass scan range: 35 to 300

Lower reporting level for core determinands: <10 µg/l

Core determinands (CD): Chlorobenzene, trichloroethene, tetrachloroethene, 1,2 dichlorobenzene

Precision % (on CD): 25 at 100 µg/l

Bias % (on CD): 20

Spiking recovery % (on CD): >50

Internal standards (IS): For example, pentafluorobenzene, difluorobenzene, chlorobenzene-d5, 1,4-dichlorobenzene-d4 (required to overlap with semi-volatile analysis). Surrogates, for example, BCTFE, fluorobenzene, p-bromofluorobenzene (BFB), dibromofluorometane, toluene-d8. Use a minimum of 3 surrogates.

Calibration: Normal MS tune or sensitivity checks. Calibrate using CD or IS.

Minimum quality control (QC) requirements: 1 aminoquinolines chromatography (AQC) sample (CD at ~ 100 µg/l plus IS) with every 10 samples, taken throughout the entire procedure

Reporting: Report all peaks with a library match confidence of >80%

Libraries: NIST, Wiley

Semi-volatiles

Basis of test: Liquid or liquid extraction (for example, dichloromethane (DCM), iso-hexane, hexane) at pH ~7 and pH>11, followed by GCMS full scan E1 mode

Mass scan range: 35 to 650

Lower reporting level for core determinands: <10 µg/l

Core determinands (CD): Aldrin, pentachlorobenzene, malathion, trifluralin, atrazine

Precision % (on CD): 25 at 100 µg/l

Bias % (on CD): 20

Spiking recovery % (on CD): >50

Internal standards (IS): For example, 1,4-dichlorobenzene-d4 (required to overlap with semi-volatile analysis), naphthalene-d8, phenanthrened10, perylene-d12. Surrogates, for example, decafluorobiphenyl, 4- fluoroaniline, 2-fluoronaphthalene. Use a minimum of 3 surrogates.

Calibration: Normal MS tune or sensitivity checks. Calibrate using CD or IS.

Minimum QC requirements: 1 AQC sample (CD at ~ 100 µg/l plus IS) with every 10 samples, taken throughout the entire procedure

Reporting: Report all peaks with a library match confidence of >80%

Libraries: NIST, Wiley

Semi-volatiles – derivatised

Basis of test: Liquid/liquid extraction (for example, DCM, iso-hexane, hexane) at pH

Mass scan range: 35 to 650

Lower reporting level for core determinands: <10 µg/l

Core determinands (CD): 2-chlorophenol, dichlorprop, PCP, bromoxynil, 2,4,6-trichlorophenol, ioxynil

Precision % (on CD): 25 at 100 µg/l

Bias % (on CD): 20

Spiking recovery % (on CD): <50

Internal standards (IS): 1,4-dichlorobenzene-d4, naphthalene-d8, phenanthrene-d10, chrysene-d12, perylene-d12. Surrogates, for example, 2,3,5,6- tetrafluorobenzoic acid, 1,2,3-trichloropropane, 4,4-dibromooctafluorobiphenyl, 2,4,5,6-tetrachloro-m-xylene. Use a minimum of 2 surrogates.

Calibration: Normal MS tune/sensitivity checks. Calibrate using CD or IS.

Minimum QC requirements: 1 AQC sample (CD at ~ 100 µg/l plus IS) with every 10 samples, taken throughout the entire procedure

Reporting: Report all peaks with a library match confidence of >80%

Libraries: NIST, Wiley

Laboratories using diazomethane should be aware of the extreme health and safety hazards associated with this reagent and have effective risk-management measures in place. Tetramethyl anilinium hydroxide (TMAH) has proved to be an effective alternative methylating agent with less significant health and safety hazards, which are more easily controlled.

Organotin compounds

Basis of test: Liquid/liquid extraction (for example, toluene, hexane/tropolone and so on) followed by electrothermal atomic absorption spectrometry (EAAS - for example, SCA 1992 method, ISBN 9 780117 523609) or GC-MS/FPD/AED

Lower reporting level: <1 µg/l

Core determinands (CD): bis(tributyltin) oxide or tributyltin chloride, triphenyltin chloride

Precision % (on CD): 10 at 10 µg/l or 25 at 0.1 μg/l

Bias % (on CD): 10

Spiking recovery % (on CD): >85

Calibration: Normal instrument tune or sensitivity checks. Calibrate using CD standard with IS standard when undertaking GC procedures.

Minimum QC requirements: 1 AQC sample (CD at ~ 10 µg/l, or lower for GC procedure, for example, 0.1μg/l) with every 10 samples, taken throughout the entire procedure.

Reporting: Report as total organotin (EAAS) or as individual compounds for GC procedure

Mercury

Basis of test: Mercury compounds reduced to elemental mercury (for example, using stannous chloride) then measured by AFS or Cold Vapour AAS

Lower reporting level: <1 µg/l

Core determinands (CD): Mercury (II) nitrate

Precision % (on CD): 10 at 10 µg/l

Bias % (on CD): 10

Spiking recovery % (on CD): >75

Calibration: Normal instrument tune or sensitivity checks. Calibrate using CD.

Minimum QC requirements: 1 AQC sample (CD at ~ 10 µg/l) with every 10 samples, plus spiking recovery for each sample

Reporting: Report as total mercury

Cadmium

Basis of test: Cadmium compounds are brought into solution by acid digestion (for example, HNO3) then measured by ICP or EAAS

Lower reporting level: <1 µg/l

Core determinands (CD): Cadmium chloride

Precision % (on CD): 10 at 10 µg/l

Bias % (on CD): 10

Spiking recovery % (on CD): >75

Calibration: Normal instrument tune or sensitivity checks. Calibrate using CD.

Minimum QC requirements: 1 AQC sample (CD at ~ 10 µg/l) with every 10 samples, plus spiking recovery for each sample matrix

Reporting: Report as total cadmium