Review your hydrogeological risk assessment
Source: gov.uk (2025-05-14)

What you need to include in your review of the site hydrogeological risk assessment and how to structure your report.

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

Even if your permit says you should review your HRA every 4 years, you should read this to now mean every 6 years.

If you’re not sure when you need to send your review to the Environment Agency, you must contact your local Environment Agency office (https://www.gov.uk/government/organisations/environment-agency#org-contacts) and agree a date with them.

Your HRA review must assess whether your assumptions and predictions remain valid from:
- the HRA you submitted to support your original permit application
- any subsequent HRA submitted and agreed through a permit variation application
- any subsequent HRA review
Your HRA review must assess the site-specific monitoring data you have collected against either:
- the values you used during your initial permit application
- any revised values you used in a subsequent variation application
You must include an assessment of the pollutant concentrations in your leachate or, for landfills for inert waste and deposit for recovery sites, waste acceptance records.

You must assess the monitored and recorded values against the values you used in any predictive modelling. You must also review the pollutant concentrations you monitored in groundwater and surface water against the data you used to set your current permit compliance limits. You must confirm whether these remain valid.

Where your HRA review concludes that there will be an increase in the predicted or modelled impact on groundwater or surface water quality, you must:
- confirm that your technical precautions are effective
- provide details of what measures you will put in place to mitigate any unacceptable emissions
If your HRA review concludes that there is no predicted or modelled impact, and the site is meeting the requirements of the permit, you do not need to apply to vary (change) your permit.

You must apply to vary your permit if you want to change any compliance limit or any element of the compliance limit. For example, the:
- design and location of your compliance monitoring points
- chemical substances you monitor
- monitoring frequency
You must submit a revised HRA to vary your permit. A HRA review will not contain the required level of detail to be acceptable for this purpose. Read what to include in your hydrogeological risk assessment (https://www.gov.uk/guidance/landfill-operators-environmental-permits/what-to-include-in-your-hydrogeological-risk-assessment) to help you develop your HRA for your application to vary your permit.

Where you submit an updated HRA report to support a permit variation, you must include any updated information or data collected between the original HRA or any subsequent HRA review and the variation application.

Unless otherwise agreed with your local Environment Agency office (https://www.gov.uk/government/organisations/environment-agency#org-contacts), an HRA submitted to support a permit variation will not meet the requirements of this guidance for the HRA review permit condition.

Where your site is closed

Where you definitely close your landfill site, you must agree your closure report with your local Environment Agency office (https://www.gov.uk/government/organisations/environment-agency#org-contacts). You can agree to changes in your operating techniques or management plans, which may include monitoring frequencies, as part of this process and will not need to vary your permit.

Read Close your landfill (https://www.gov.uk/guidance/landfill-operators-environmental-permits/close-your-landfill-site).

Review your HRA at landfill sites for inert waste and deposit for recovery activities

Where your permit requires it, you must review your HRA for a landfill site for inert waste or deposit for recovery activity. You will normally only need to do a qualitative (https://www.gov.uk/guidance/groundwater-risk-assessment-for-your-environmental-permit#qualitative-risk-screening) or generic quantitative (https://www.gov.uk/guidance/groundwater-risk-assessment-for-your-environmental-permit#generic-quantitative-risk-assessment) risk assessment.

There will not normally be any leachate data to compare with original input parameters for modelling. You may be able to use waste acceptance records, for example leach test results. If leachate data is available, you should assess whether this changes the potential impact posed by your site.

How to structure your HRA review report

Your HRA review report must include each of the following sections.

You must include an entry in each section, even if it is to confirm that a feature is not relevant to your site.

The Environment Agency accepts that you may not need to complete some of the sections.

1. Introduction

Your introduction must include:
- the name of the operator, site name and address and the environmental permit number
- the name and address of the agent who completed the risk assessment
- the objective of the report
- report context – include background information and an outline of the site, including details of the current operational phase
- site setting, including the current and historic waste types and how it relates to historically operated areas of landfill or deposit for recovery activities
- the date and reference of the original HRA for the site
- the date and reference of any previous HRA reviews
- the date and reference of the current permit and a summary of any improvement conditions
- cross reference to an appropriate conceptual site model (https://www.gov.uk/guidance/groundwater-risk-assessment-for-your-environmental-permit#develop-your-conceptual-model) (CSM), environmental setting and installation design (https://www.gov.uk/guidance/landfill-operators-environmental-permits/what-to-include-in-your-environmental-setting-and-installation-design-report) (ESID) report or environmental setting and site design (https://www.gov.uk/guidance/landfill-operators-environmental-permits/what-to-include-in-your-environmental-setting-and-site-design-report) (ESSD) report, leachate management plan (https://www.gov.uk/guidance/landfill-operators-environmental-permits/develop-and-maintain-management-plans#manage-leachate) and monitoring management plan (https://www.gov.uk/guidance/landfill-operators-environmental-permits/monitor-and-report-your-performance)
2. Review of your conceptual site model, leachate management plan and monitoring management plan

Your HRA review must contain a review of the CSM, with reference to the leachate management plan and monitoring management plan to confirm they continue to reflect the situation at the site.

It must include summary details, cross referenced to the ESID or ESSD report. You must include other supporting documents if you have not provided an ESID or ESSD report before.

You must confirm:

a) the source term

You must confirm:
- any relevant alterations or amendments to the construction, operation, capping and restoration of the site
- that the methods you use to measure leachate levels are consistent with the leachate management plan or monitoring management plan
- that the recorded leachate levels still apply or differ from those previously recorded
- that site-specific leachate data or waste acceptance records reflect the modelled input parameters presented in the original application, or any model updated by subsequent HRA reviews
b) the pathways

You must:
- include a summary of all previously identified natural or man-made pathways, including their nature and characteristics (such as the attenuating properties of the underlying geology, and whether your assumptions still apply since you prepared your initial HRA or any subsequent HRA reviews)
- confirm if local groundwater levels have increased or decreased, for example due to a change in the groundwater pumping regime (on or off site)
- confirm that local groundwater is flowing in the direction previously identified
- confirm that local groundwater and surface water quality is the same as previously identified
For non-hazardous or hazardous sub-water table landfills, your HRA review must assess the same criteria. You must also confirm that there remains an inward hydraulic gradient around the whole site.

For inert landfills and deposit for recovery sites below the water table, the Environment Agency accepts that there is no inward hydraulic gradient. Any water within the waste body would normally reflect natural groundwater levels.

c) the receptors

You must confirm:
- that the receptors you identified and assessed in the original HRA or subsequent HRA reviews are still valid
- if there are any new receptors, for example a habitat site fed by groundwater, or a change in classification of the habitat site or local abstraction borehole in the outflow region
- any change in aquifer classification, groundwater levels or direction of groundwater flow
- the suitability of previously used environmental assessment levels (https://www.gov.uk/guidance/landfill-developments-groundwater-risk-assessment-for-leachate#compliance-points)
- the main parameters you are monitoring for in groundwater around the site or surface water – state whether these are still appropriate against leachate data or waste acceptance records
3. Modelling approach

Justification for the modelling approach and software

You must review:

the previous risk assessment methodology and determine whether the complexity level (https://www.gov.uk/guidance/landfill-developments-groundwater-risk-assessment-for-leachate#risk-assessment-level-guide) remains the same

previous risk assessment scenarios relating to different stages of the lifecycle of the site and decide if they still apply, such as potential degradation of the leachate drainage layer or changes to groundwater or sea levels
- the previously selected modelling approach and software – confirm it still applies for the considered scenarios and hydrogeological conditions (you must assess the whole lifecycle of the site)
- the justification for confidence levels within any existing stochastic modelling
- the model and its suitability to identify and represent receptors and compliance criteria
Where you do a quantitative risk assessment (https://www.gov.uk/guidance/groundwater-risk-assessment-for-your-environmental-permit#generic-quantitative-risk-assessment) you must normally use the following models for assessing the risk to groundwater (providing the CSM is appropriate for the site):
- the most up to date version of LandSim for sites above the water table
- contaminant fluxes for hydraulic containment spreadsheet (https://www.gov.uk/government/publications/contaminant-fluxes-from-hydraulic-containment-landfills-a-review) where part or all of your site is below the water table
- the most up to date version of ConSim for inert waste landfills and deposit for recovery sites above the water table,
If you use an alternative modelling approach you must show that it is an equivalent standard.

You must send the Environment Agency a digital copy of any model you use.

Model parameterisation

Your HRA review must include a table that includes:
- all the input parameters you previously used and the justifications you used for the last HRA
- an assessment of whether the previously used parameters and any probability distribution functions still apply
- an assessment, where applicable, of whether any changes to the input parameters require further modelling on a parameter by parameter basis
- appropriate justification to support your proposed changes to the model parameters
You must provide all monitoring data in a spreadsheet.

4. Hydrogeological risk assessment

You must review the following.

a) Emissions to groundwater

You must review the site-specific monitoring data. Your HRA review must confirm that:
- predicted concentrations of hazardous substances (https://www.gov.uk/government/publications/protect-groundwater-and-prevent-groundwater-pollution/protect-groundwater-and-prevent-groundwater-pollution#hazardous-substances) at the compliance points will remain within permitted compliance limits
- measured concentrations of hazardous substances at the compliance points are below the permitted compliance limit and are not polluting groundwater or surface water
- predicted concentrations of non-hazardous pollutants (https://www.gov.uk/government/publications/protect-groundwater-and-prevent-groundwater-pollution/protect-groundwater-and-prevent-groundwater-pollution#non-hazardous-pollutants) at the compliance points will remain within permitted compliance limits
- measured concentrations of non-hazardous pollutants at the compliance points are below the permitted compliance limit and are not causing pollution of groundwater or surface water
b) Sensitivity analysis

If you carry out additional modelling as part of your HRA review, you must include a sensitivity analysis of the predicted concentrations.

Your sensitivity analysis must include:
- model runs to simulate different ranges of input parameter values – you must explain why you used those ranges
- any assessment limitations, for example any uncertainties or necessary safety factors
If your HRA review confirms that you do not need additional modelling, you must review the sensitivity analyses you did on the parameters in the site’s original HRA or previous reviews.

c) Technical precautions

You must include a review of the technical precautions needed to prevent unacceptable discharges of hazardous substances (https://www.gov.uk/government/publications/protect-groundwater-and-prevent-groundwater-pollution/protect-groundwater-and-prevent-groundwater-pollution#hazardous-substances) and non-hazardous pollutants (https://www.gov.uk/government/publications/protect-groundwater-and-prevent-groundwater-pollution/protect-groundwater-and-prevent-groundwater-pollution#non-hazardous-pollutants) to groundwater or surface water.

This must include, where applicable, a review of:
- capping
- the naturally occurring or enhanced geological barrier or attenuation layer
- the lining design and leak detection
- leachate drainage and recirculation systems
- leachate head control
- groundwater and surface water management systems
Monitoring is a technical precaution. You must consider it in more detail when you review your monitoring management plan.

5. Infrastructure integrity

You must confirm that the monitoring infrastructure will provide representative samples and remains suitable. The data you send to the Environment Agency must represent the media you are sampling, for example leachate or groundwater.

Your HRA review must confirm that your monitoring infrastructure has been inspected and maintained or replaced if necessary. You must confirm whether your monitoring infrastructure is original or if you have replaced it.

Your HRA review must include a summary of any changes to monitoring infrastructure at your site during the 6 year review period.

6. Monitoring

Where required by your permit, you must monitor groundwater, leachate and surface water (https://www.gov.uk/guidance/landfill-operators-environmental-permits/monitor-and-report-your-performance#what-you-need-to-monitor).

Your HRA review must confirm that the existing monitoring remains appropriate. This includes the suitability of the compliance limits.

You must include details of your monitoring scheme, including:
- the monitoring objectives and a review of whether you are meeting them
- an overview of the number and location of monitoring points and whether these points are in the right place – provide representative samples of the media you are sampling
- cross references to your monitoring management plan, including a plan showing the location of all existing monitoring points – include all monitoring points with data collected over the review period and highlight any monitoring points that have been installed since the initial HRA or last HRA review
- a summary of any compliance limit breaches and confirmation that you notified the Environment Agency where required by your permit
You must include details and reasons for any changes to the monitoring scheme.

7. Conclusions

Your HRA review must confirm that the:
- design of your site continues to prevent unacceptable discharges (https://www.gov.uk/government/publications/protect-groundwater-and-prevent-groundwater-pollution/protect-groundwater-and-prevent-groundwater-pollution#hazardous-substances) and emissions
- monitoring management plan, assessment levels and compliance limits (https://www.gov.uk/guidance/landfill-operators-environmental-permits/monitor-and-report-your-performance#set-assessment-levels-and-compliance-limits) for groundwater, leachate and surface water (where applicable) remains suitable
8. Tables

You must normally include tables in your HRA review. Tables can summarise lots of information or data into a manageable format. The number and content of your tables will reflect the circumstances at your site.

You must normally present your tables in the following way.

Table 1

Show the date and nature of any improvement conditions.

Table 2

Summarise the design of each area or phase of the site, including the design of the lining, leachate management and capping systems.

Table 3

Show the conceptual site model scenarios.

Table 4

Summarise changes to the conceptual site model. Include a summary of the relevant source, pathway and receptor terms, and schematic, annotated cross sections.

Table 5

Show the relevant priority substances and environmental assessment limits.

Table 6

Show the model parameterisation.

Table 7

Show the risk based monitoring scheme for groundwater, leachate and surface water.

Table 8

Show the model validation exercise. Compare the output against observed site conditions and monitoring data.

Table 9

Show the modelling results and potential concentrations of hazardous substances and non-hazardous pollutants at the compliance points.

Table 10

Show the compliance limits for hazardous substances and non-hazardous pollutants for groundwater, leachate and surface water.

9. Drawings

You must base your HRA review on the following plans or drawings. One drawing can provide information for more than one part if the drawing is clearly labelled.

Use recognised scales (such as 1:1250) for all drawings, maps or plans to show the relevant details. All levels must be in m AOD (metres Above Ordnance Datum).

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
Drawing 1: site location plan

A plan showing the location of the site.

Drawing 2: site plan

A plan showing:
- the location of each cell or phase – indicate which ones are filled (specify permanent or temporary capping) and where you have remaining void capacity
- the location of all monitoring points, potential receptors, compliance points and pathways
- seasonal minimum and maximum groundwater level contours for a representative monitoring round in the period covered by the review
Drawing 3: hydrogeological cross sections

A schematic and annotated drawing showing:
- details of formation levels, leachate levels, engineering design and current topography
- the geology
- minimum and maximum groundwater levels and flow directions
- the location of all monitoring points and the nature and location of all natural and man-made pathways and potential receptors
Each cross section should be no larger than A3.

Drawing 3: conceptual site model scenarios

A drawing showing the conceptual site model scenarios if:
- no modelling is required – include the original conceptual site model scenarios from the initial HRA
- modelling is required – include the revised conceptual site model scenarios
10. Appendices

You must include all the information you used to complete your report, including all the numerical and analytical models you refer to, and their results, in digital format in the appendices.

You must normally include the following.

Appendix A

Leachate hydrographs with a linear scale that shows the permitted compliance limit. Include a digital copy of the data you used to produce the hydrographs.

Appendix B

A summary of any pumping trials, pumping suspension or recovery trials and dates carried out.

Appendix C

Leachate quality information.

Appendix D

Surface water quality information.

Appendix E

Groundwater hydrographs with a linear scale. Include a digital copy of the data you used to produce the hydrographs.

Appendix F

Groundwater quality information.

If you do additional modelling include the following.

Appendix G

Digital copies of all the models you used in the HRA review.

Appendix H

Hard copies of the models and inputs you used in the further assessment.

Appendix I

Results of any sensitivity analysis you carried out for the site, unless specified within the text.