Land contamination: risk management

Stage 1: Risk assessment

How to do a land contamination risk assessment (RA).

Before you start RA

You can only do a land contamination risk assessment if you’re a suitably qualified competent professional.

The 3 tiers of RA are:

  1. Preliminary risk assessment (PRA) - first tier of RA that develops the outline conceptual model (CM) and establishes whether there are any potentially unacceptable risks.
  2. Generic quantitative risk assessment (GQRA) - carried out using generic assessment criteria and assumptions to estimate risk.
  3. Detailed quantitative risk assessment (DQRA) - carried out using detailed site-specific information to estimate risk.

In all cases, you must start with a PRA.

The RA stage is an iterative process. It’s normally followed in order but depending on the level of risk, you can jump a tier or proceed to the options appraisal (OA) stage. For example, you can proceed from a PRA to DQRA or OA.

If you do not follow the tiers in order, for example you proceed direct to the OA stage, you’ll still need to collect the detailed information required by the GQRA and DQRA.

To do a land contamination RA you must:

  • identify the reasons for doing the RA
  • identify contaminants and pollutant linkages
  • assess and evaluate the risk to establish whether there is an unacceptable risk

When you’ve completed the RA, if there are unacceptable risks you must follow stages 2 and 3 in order.

If you establish that the risks are acceptable, with agreement from the relevant regulator (such as the local authority or the Environment Agency) you can end the process.

Technical approach to risk assessment

For each tier of RA you must:

  1. Identify the hazard - establish contaminant sources.
  2. Assess the hazard - use a source-pathway-receptor (S-P-R) pollutant linkage approach to find out if there is the potential for unacceptable risk.
  3. Estimate the risk - predict what degree of harm or pollution might result and how likely it is to occur by using the tiered approach to risk assessment.
  4. Evaluate the risk - decide whether a risk is unacceptable.

The meaning of the terms are:

  • hazard: a property or situation that in particular circumstances could lead to harm or pollution
  • risk: a combination of the probability, or frequency of occurrence of a defined hazard and the magnitude of the consequences of the occurrence
  • risk assessment: the formal process of identifying, assessing and evaluating the health and environmental risks that may be associated with a hazard
  • risk management: the formal process of identifying, assessing and determining risks, and the selection and implementation of actions to mitigate them

Evaluate the risk

You will evaluate the risk using risk assessment evaluation criteria.

These are the parameters used to judge whether particular harm or pollution needs further assessment or is unacceptable. The criteria you use will relate to the type of harm or pollution you’re dealing with. The receptors involved could be controlled waters, human health, ecosystems or property. Any evaluation criteria you use must be relevant to your site.

The exact choice of evaluation criteria will depend on:

  • the reasons for doing the RA and the regulatory context such as Part 2A
  • the CM and pollutant linkages present
  • any criteria set by regulators
  • any advisory requirements such as from Public Health England
  • the degree of confidence and precaution required
  • the level of confidence required to judge whether a risk is unacceptable
  • how you’ve used or developed more detailed assessment criteria in the later tiers of RA
  • the availability of robust scientific data
  • how much is known - for example, about the pathway mechanism and how the contaminants affect receptors
  • any practical reasons such as being able to measure or predict against the criteria

For example, for Part 2A you will need to evaluate whether the presence of contamination is causing significant harm or the significant possibility of significant harm to human health. The evaluation criteria you use will establish whether the site is contaminated land under that regime.

The criteria are measures of a risk of harm or pollution to the receptor and can be:

  • minimal or negligible
  • tolerable or acceptable
  • unacceptable

Evaluation criteria are set in relation to a level of harm or pollution to the specified receptor. They may be translated into:

  • absolute standards or recommended maximum values and are measured in relation to the receptor - for example, a health criteria value for the intake of a substance measured in relation to the receptor
  • guideline values or mandatory values for the concentrations of the contaminant in the soil, groundwater or air

For PRA, you will normally evaluate the risks qualitatively.

If you progress to a quantitative GQRA or DQRA, you will use evaluation criteria to judge whether particular harm or pollution needs further assessment or is unacceptable.

Evaluation criteria include GQRA generic assessment criteria (GAC) and DQRA site-specific assessment criteria (SSAC).

For example, evaluation criteria for the risk to human health from exposure to contaminants are often based on direct intakes via pathways such as ingestion and inhalation. In this context, GAC and SSAC are the calculated levels in soil above which may present an unacceptable risk of harm to human health. The evaluation criteria will take into account different land uses and the type and sensitivity of the human health receptor.

If GAC or SSAC are exceeded, you will need to evaluate if that level of risk is acceptable and whether further assessment is needed.

Evaluation criteria may also be used directly. For example, using a drinking water standard to evaluate whether the predicted level of a contaminant in groundwater at a compliance point is acceptable.

It’s important that you understand any underlying assumptions and take them into account when you interpret the results of your GQRA or DQRA.

Examples of evaluation criteria include:

  • category 4 screening levels (C4SL) and LQM/CIEH Suitable for Use Levels (S4ULs)
  • human health toxicological assessment of contaminants in soil (SR2) tolerable daily intakes and index doses
  • SSACs derived using remedial targets methodology (RTM) and a regulatory compliance point
  • drinking water standards
  • ecosystem end-points which take into account the ecological value of a site - for example, used under Part 2A for assessing significant harm to ecosystems

You:

Tier 1: Preliminary risk assessment (PRA)

You must always start with a PRA. This will establish whether there are any potentially unacceptable risks arising from contamination at the site.

To complete a PRA you need to:

  • define the overall site objectives
  • collect current and historical information about the site and the potential contaminants expected to be present
  • develop an outline CM
  • assess the risks qualitatively
  • record your findings in your PRA report and decide what further action is needed

Define the overall site objectives

You must understand the reason for doing the assessment from the person who has commissioned it. This could be the:

  • land owner
  • regulator
  • potential purchaser
  • developer
  • ‘appropriate person’ for Part 2A

You must understand their objectives and the scope of assessment required.

For example:

  • a local authority may require a limited assessment because the site is of a lower priority than other Part 2A sites in its inspection strategy
  • developers may require a more detailed assessment to fulfil a planning condition
  • the assessment of a former industrial site for redevelopment (as part of a planning application) may have a different scope than one carried out for valuation purposes

Possible overall objectives for the site could be to:

  • meet regulatory requirements or to anticipate regulatory action
  • assess the site for Part 2A
  • ensure the site is suitable for redevelopment
  • take voluntary action to manage the risks
  • assess the site to support funding decisions
  • assess the site to comply with or surrender a permit
  • get a valuation, for example for insurance, sale or transfer purposes or to address any liability issues
  • reassess any previous assessment of the site

You will need to know the required timescales, for example if it’s:

  • an immediate, medium or long term risk
  • related to a current use or future change of use of the site

You will need to establish the level of technical confidence needed, for example if it’s:

  • low, medium or high
  • preliminary, indicative or comprehensive

You will need to understand any constraints on time or cost.

Collect information for PRA

You collect information via a:

  • desk study
  • site walkover

Use this information to:

  • interpret historical, archived and current information to establish the location of previous site activities
  • understand the environmental setting of the site
  • identify areas or zones that contain distinct and different types of contamination
  • identify pollutant linkages using a S-P-R approach
  • develop an outline CM
  • scope out the likelihood of needing an appropriate site investigation to determine the extent of contamination if you progress to the next tier or stage

Find detailed guidance for PRA on the CL:AIRE WALL - see risk assessment - preliminary (INFO-RA1).

The specific information you need will depend on the reasons and objectives for the PRA. You can use the information below as a checklist.

Desk study checklist

From a desk study find out:

  • the history of the site
  • any pollution incidents, spills, accidents or regulatory actions
  • details of any current or past permits, licences or authorisations
  • details of any previous investigations or remediation
  • any chemical or biological information from for example, previous site monitoring reports
  • if available, natural background contamination information, such as radon gas
  • if any audit reports have been done
  • the location of historical landfill sites
  • the presence or proximity of sensitive ecological receptors such as special protection areas
  • the location of any protected areas of countryside
  • the presence of any archaeological or heritage sites such as scheduled ancient monuments
  • information on other specific Part 2A receptors such as crops or property
  • any proposed future changes to land use such as planning applications

Find out geological, hydrogeological and hydrological information including:

  • made ground, drift deposits, bedrock
  • geological features such as faults
  • presence of groundwater - unconfined, confined aquifer or a mixture of both
  • aquifer type - principal, secondary or unproductive strata
  • sensitive groundwater locations such as source protection zones or safeguard zones
  • the vulnerability of the groundwater to pollution
  • the likelihood of perched groundwater
  • abstraction points or wells on or close to site - you must include private water supplies
  • presence of and proximity to other controlled waters such as surface water and coastal
  • any available water quality information
  • information on characteristics such as the likely groundwater flow direction

To find out more about groundwater see the groundwater protection document collection.

Site walkover checklist

From a site walkover record information such as the:

  • current use and status of the site - occupied or vacant
  • general housekeeping, condition of site and surrounding land use
  • presence of visual surface staining and odours
  • topography and surface condition - open ground, hardstanding and other geotechnical or surface features
  • local surface water features
  • ecology
  • presence and type of vegetation
  • presence and extent of any invasive plant species
  • buildings and below or above ground structures such as fuel tanks
  • above and likely below ground services
  • access and security

Record details of possible S-P-R pollutant linkages and effects, including:

  • type, extent, location and behaviour of potential contaminants
  • information on site drainage and other man-made potential pollutant pathways
  • type of receptor you are dealing with - for example, human health, controlled waters, ecology or property
  • characteristics of the people and the environment potentially affected by the contaminants

Use this information, combined with the overall site objectives, to identify S-P-R pollutant linkages and develop your outline CM.

Identify source-pathway-receptor pollutant linkages

Use an S-P-R approach to work out the potential pollutant linkages. Identify the:

  • source - a contaminant or pollutant that is in, on or under the land and that has the potential to cause harm or pollution
  • pathways - a route by which a receptor is or could be affected by a contaminant
  • receptors - something that could be adversely affected by a contaminant, for example a person, controlled waters, an organism, an ecosystem, or Part 2A receptors such as buildings, crops or animals

The terms source, pollutant and contaminant have the same meaning.

For Part 2A, the definition of contaminant is a substance which is in, on or under the land which has the potential to cause significant:

  • harm to a relevant receptor
  • pollution of controlled waters

For more details on Part 2A see the contaminated land statutory guidance.

Pathways will be specific to the receptor type. For example, they could be:

  • ingestion, inhalation, dermal contact for human health receptors
  • infiltration and contaminant migration via permeable strata or the unsaturated zone for groundwater contamination
  • gas migration of volatile hydrocarbons into buildings
  • direct contact and uptake by plants

A pollutant linkage must be present for there to be a S-P-R relationship. Without a pollutant linkage, there is not a risk - even if a contaminant is present.

You must find out if there are one or more pollutant linkages and how each is related. For example:

  • the same contaminant may be linked to 2 or more types of receptor
  • different contaminants may affect the same receptor
  • a new pollutant linkage may arise by changes over time, such as ongoing migration of contaminants or a change of land use

Conceptual model

Use the information you’ve collected to create an outline CM. It’s a representation of the characteristics of the site and shows the possible relationships between contaminants, pathways and receptors.

You will need to refine your CM as you progress through the further tiers and stages. It will form the basis of your assessment and will help you evaluate the risks correctly.

You can present a CM in different ways, such as a:

  • written description of the site
  • tabular or matrix description
  • drawing or other diagrammatic illustration

You may combine one or more of these formats.

You must show:

  • S-P-R pollutant linkages - presence and relationship between contaminants, pathways and receptors
  • the subsurface - geology and hydrogeology
  • more detailed information as it becomes available such as complex flow regimes and soluble transport mechanisms

You can use the CM to work out and show:

  • the characteristics of the site
  • what risks may result
  • uncertainties and gaps in information and any further assessment needed to address them

As you progress through the risk management process, you will have to refine and update the CM. You can:

  • do a site investigation to test and refine the CM
  • carry out monitoring to validate the CM
  • use detailed geological information such as thickness of made ground, presence of natural and superficial deposits, depth to bedrock, presence of faults
  • use detailed hydrogeological information such as hydraulic gradient, flow direction, depth to water table, hydraulic conductivity
  • address any uncertainties
  • identify potentially different areas (or zones) of a site, based on differing ground conditions, potential contamination and past, present and future uses

Find detailed information on conceptual models on the CL:AIRE WALL - see risk assessment - preliminary (INFO-RA1).

Assess the risks

For a PRA you must assess the risks qualitatively to decide whether particular harm or pollution is unacceptable. You need to base these on the:

You must base your assessment on the potential severity that the risk poses to the receptors against the likelihood of it happening.

See the following examples of qualitative PRA assessments for potential S-P-R pollutant linkages.

Example 1

Groundwater PRA:

  • contaminant - potential hydrocarbons from an old underground tank
  • pathway - migration via the unsaturated zone
  • receptor - principal aquifer

The decision will be based on the likelihood of hydrocarbons reaching groundwater.

Example 2

Human health PRA:

  • contaminant - potential metals in soil
  • pathway - inhalation, ingestion, dermal contact
  • receptor - future residents

The decision will be based on the likelihood of the metals presenting a risk to human health in a residential setting.

Conclude PRA

At the end of this tier you will need to create a decision record. This must include:

  • a summary of the objectives and reasons for doing the PRA
  • an outline CM including the basis for how you developed it
  • the potential risks - unacceptable or acceptable - and how you evaluated them
  • justification for your proposed next steps

You must decide if:

  • there’s no unacceptable risk and you can exit the process
  • more information is needed and you need to proceed to a GQRA or go direct to a DQRA
  • there’s a clear risk and you need to collect more detailed information and proceed to OA

Your decision may need approval or agreement from the regulator. For example, approval of a Part 2A obligation or to satisfy a planning condition.

Produce a PRA report

See Stage 1: risk assessment reports for what to include.

You may decide to use NQMS.

Tier 2: Generic quantitative risk assessment (GQRA)

If your PRA has identified one or more potential pollutant linkages you can do a GQRA to assess these further.

You will need to:

  • establish if you can use GAC and a standard set of generic assumptions to assess the risks
  • collect more detailed information to confirm and assess any unacceptable risks

For a GQRA you must:

  • review and confirm the overall site objectives
  • define the GQRA objectives
  • identify appropriate GAC or derive new ones
  • work out what information you need to collect
  • collect information about the site by doing an appropriate site investigation
  • confirm the pollutant linkages that need to be assessed
  • decide if GAC are suitable to use
  • assess each pollutant linkage using GAC and decide if there are unacceptable risks
  • record your findings in your GQRA report and decide what further action is needed

Define the GQRA objectives

You will need to:

  • make sure the overall site objectives are still valid
  • take into account, build upon and refine the information used in the PRA
  • identify any new information as a result of more detailed data collection and assessment

You must consider technical and management factors.

Technical factors include the:

  • complexity of the CM and the interaction of ground, groundwater, surface water and gassing regimes
  • nature of the S-P-R pollutant linkages
  • possible combined or cumulative factors of different contaminants interacting with each other - as you collect more data this may become complex
  • potential changes in site circumstances
  • uncertainties in any previous information collected
  • methods of how you will collect and assess the data to achieve the required level of confidence

Management factors include:

  • regulatory requirements such as complying with a planning condition or a Part 2A obligation
  • management aspirations - the reasons for the GQRA must be clear, as doing it will involve an increase in cost and time
  • constraints on time and budget
  • how you will communicate the level of risk to interested parties such as site owners, regulators or members of the public
  • being able to reach agreement with stakeholders

You will need to consider:

  • the degree of confidence in the outcome of the assessment expected - it must be clear and realistic
  • the public’s perception - a more complex site and assessment may be more difficult to explain to non-specialists

Identify appropriate GAC

For a GQRA you must assess each potential pollutant linkage by comparing the contaminant concentrations against appropriate GAC.

GAC are screening criteria which are derived using a standard set of generic assumptions. They are designed to be broadly applicable to a wide range of site conditions and exposure scenarios. They must be appropriate and suitable for your site.

GACs:

  • relate to concentrations of substances in air, water or soil
  • make generic assumptions about the site characteristics, the contaminant, pathway and receptor behaviour
  • aim to simplify the RA by using a standard approach
  • are used to determine if further RA or more information is required

You may be able to use existing GAC or derive new ones.

When you use GAC you will need to consider:

  • if they are appropriate
  • how they meet the overall site objectives
  • how you will evaluate the risks

You must take into account if the GAC are:

  • too conservative - this may result in an unnecessary and more detailed RA or remediation
  • not conservative enough - this would result in the assessment of the risk being incorrect

GAC must apply to the:

  • type and form of contaminant you’re assessing
  • relevant media - soil, water, dust, sediments, air and parameters such as soil type, pH
  • nature and characteristics of the pathway
  • land use - for example, human health criteria are typically more stringent for residential end use than for commercial or public open space
  • receptor - including its characteristics, vulnerability or use

If you cannot use existing or derive GAC you will need to do a DQRA or proceed to the options appraisal stage.

Confirm if GAC are suitable

Most GAC are designed to assess risks from specific pollutant linkages. For example, you could be assessing the long term risk to human health from direct contact with heavy metals in soil. In this case, you could use soil guideline values (SGVs).

SGVs are an example of existing GACs you can use. They were derived by the Environment Agency using the CLEA model.

To find out more about SGVs see:

Use existing GAC

You will need to identify if existing GAC are suitable to assess each potential pollutant linkage.

Some examples of existing GAC you can use are:

You must use caution if a GAC is adapted for a different type of pollutant linkage.

If you use a standard intended for a different purpose this could result in over conservative or under conservative conclusions. For example, you must only use values such as DWS or EQS after you’ve carefully considered if their inclusion is relevant to your site, the pollutant linkages, and the legislative context.

If you are dealing with ecological receptors you can find detailed information on the CL:AIRE WALL - see assessing risks to ecosystems (INFO-RA2-5).

Derive new GAC

In some cases, you may be able to derive GAC. You will need to use conservative assumptions about the behaviour of the potential S-P-R pollutant linkages.

If you need to derive GAC, you must:

  • develop a standard set of generic assumptions that describe the potential linkages appropriately for the GAC
  • work out what information you need to collect about the potential linkages and other properties of the site and its setting
  • check that the new GAC is consistent with other GAC applied to similar pollutant linkages
  • record the information and assumptions you used to derive a new GAC
  • set out any requirements for how the new GAC will be applied appropriately

You can consider using some models and formulae that are normally used in a DQRA. These are designed for detailed assessments. They must be used in a quantitative way.

Examples of risk assessment models you can use are:

When you develop GAC using these models you must:

  • have sufficient specialist knowledge and exercise care
  • use appropriate and justified information sources for additional parameters such as chemical properties
  • keep the assessment generic and understand the limitations at this level of assessment

Decide what information you need for GQRA

Having selected existing or derived new GAC, you will need to collect relevant information so that you can use them to assess the risks. You will use this information to:

  • confirm which pollutant linkages need to be assessed
  • compare the contaminant concentrations from the site investigation against the relevant GAC

The GQRA information you need to collect will build upon the information you gathered from your PRA and will depend on the:

  • potential contaminants you’re assessing - for example, information for assessing risks from a solvent plume impacting groundwater will be different to information for assessing heavy metals in soils
  • complexity of the contamination - for example, if there are mixtures of contaminants from multiple sources
  • type of receptor - for example, human health, controlled waters, ecosystems, crops or property will all require different information
  • complexity and scale of the site

You may need to collect more detailed information on:

  • contaminants - types, lateral and vertical extent, chemical form, concentrations, potential for contaminant leaching and migration, background levels
  • ground - type and geology
  • parameters you may need to use such as soil organic matter and pH
  • any gassing regime prevailing at the site
  • receptors - location, types, relationship to site, vulnerability to particular substances, existing condition and history
  • pathways - location, type, number and extent
  • nature of pathways - such as direct contact, inhalation or migration

Collect more detailed information on hydrogeological and hydrological properties including:

  • depth to water table
  • thickness of saturated zone
  • presence of perched groundwater
  • groundwater chemistry
  • hydraulic gradient
  • groundwater flow direction
  • direction and rate of flow of surface water
  • seasonal variations in groundwater table and surface waters
  • surface water chemistry

You may also need further information on other site conditions such as:

  • any remediation already done
  • weather and natural patterns - such as seasonal variations in water levels, tidal impacts and potential for or evidence of previous flooding
  • presence of structures and buried services

Use this information to refine the CM and confirm the pollutant linkages to improve your understanding of the site.

You must use the correct sampling and analysis procedures. This includes how you preserve and transport samples from site to the laboratory.

You must use the Environment Agency’s monitoring certification scheme (MCERTS).

Collect GQRA information

For a GQRA you will need to design and carry out an intrusive site investigation. You may need to phase this for complex sites. You will need an appropriate sampling and analytical strategy to get information on contaminant concentrations. You will compare these against relevant GAC.

You must consider the practicability, costs, effectiveness and benefits of site investigation.

If it is not practicable or cost effective to collect all the information you may have to go back and review the overall site objectives. In some cases, it may be more cost effective to move straight to options appraisal stage, but this will mean that you will need to amend the risk assessment objectives.

The information you collect must be relevant, sufficient, reliable and transparent to support the use of the selected GAC and the type of receptor you are dealing with.

You will need to produce a site investigation report or present the results in your GQRA report.

Confirm pollutant linkages to assess

Use the site investigation information you’ve collected to confirm which potential S-P-R pollutant linkages you will assess. You may:

  • be able to rule out some of the linkages
  • need to add some new linkages

You must also check if there are any changes in site circumstances that might affect which linkages need to be assessed.

You must update the CM with your findings and record these decisions.

If you do not have sufficient information to confirm or rule out linkages then you may:

Assess the risks

You must compare the contaminant concentrations from the site investigation against the relevant GAC.

You must consider:

  • how rigid the GAC are - for example, if they’re advisory screening values or strict limit values
  • how much any exceedance matters and how it relates to how you will evaluate the risk - this may need agreement from the regulator
  • if concentrations are representative of background conditions
  • if the standard set of generic assumptions used are representative of the site
  • if there are any uncertainties associated with the GAC
  • any additional evidence that has been collected to support interpretation

You must justify how you have evaluated the risks and include this information in your GQRA report.

Conclude GQRA

At the end of this tier you will need to create a decision record. This must include the:

  • pollutant linkages you’ve identified - explain how you developed the CM for example with the site investigation results
  • GAC and the assumptions you used to assess the risks
  • potential risks - unacceptable or acceptable - and how you evaluated them
  • justification for your proposed next steps

Update the CM with confirmed RPLs.

When you’ve assessed each pollutant linkage, you must decide if:

  • the unacceptable risks have been dealt with, no further action is required and you can exit the process
  • more information is needed to address uncertainties and complete the GQRA - for example, further assessment, site investigation and monitoring
  • there’s unacceptable risks and you need to progress to DQRA or proceed direct to OA

If you proceed to OA you may need to collect more detailed information as required by DQRA.

All confirmed pollutant linkages are now called relevant pollutant linkages (RPLs) . You take these to the next tier or stage.

You must update the CM with your findings.

Your decision may need approval or agreement from the relevant regulator. For example, approval of a Part 2A obligation or to satisfy a planning condition.

Produce a GQRA report

You need to produce a:

You may decide to use the NQMS.

Tier 3: Detailed quantitative risk assessment (DQRA)

You will have identified one or more RPLs that need a detailed assessment.

You can do a DQRA:

  • where further assessment is required following a GQRA
  • for complex sites where detailed assessment is required

For a DQRA, you will need to collect detailed site-specific information to estimate the risk or to develop site-specific assessment criteria (SSAC).

To complete a DQRA you need to:

  • define the DQRA objectives
  • decide what information or tools you need to support the RA
  • collect the information
  • confirm the RPLs that need to be assessed
  • assess the risks for each RPL
  • decide if there are unacceptable risks
  • decide what further action is needed
  • record your findings in your DQRA report

You will need to identify or develop tools and criteria to estimate and evaluate the risk. This may include developing detailed SSAC or collecting information about the receptor.

Define the DQRA objectives

You will need to:

  • review and confirm that the overall site objectives are still valid
  • take into account and build on the information used so far in the RA
  • identify any new information as a result of further data collection and assessment

To be able to collect and then assess appropriate information you must define your objectives for DQRA. This may involve refining the objectives from your GQRA if you did one. You need to consider the following technical and management factors.

Technical factors include:

  • the complexity of the site, ground conditions and processes - you may need to get a more detailed understanding of particular areas or zones of the site
  • RPLs - you may need to get highly specialist information to assess the complexity, toxicity, effects and characteristics of individual linkages
  • any combined or cumulative factors - this may require specialist toxicological and environmental fate and transport knowledge
  • any potential changes in site circumstances
  • the use of risk estimation models - these need specialist knowledge
  • any uncertainty of data - such as unexpected monitoring results
  • the methods you’ll use to assess the data to achieve the required level of confidence

Management factors include:

  • regulatory requirements - the DQRA may need to support a regulatory decision
  • management aspirations - the reasons for the DQRA must be clear at the outset, as doing it will involve an increase in cost and time
  • constraints on time and budget - it may be essential to stage information collection
  • timeframe - the DQRA assessment may be more complex
  • consultation and agreement with interested parties - because of the complexity of the site more detailed discussion with different interest groups may be required
  • communication of risk - transparency is required when the approach used is explained and justified

Other factors include:

  • the expected degree of confidence of the assessment - it must be clear and realistic
  • public perception - it’s a more complex site and the assessment may be more difficult for non-specialists to understand

Decide what information to collect for DQRA

The information you will need for DQRA will depend on the:

  • contaminants being assessed
  • receptors being considered
  • complexity of the site, for example if there are mixtures of contaminants

You will need to collect more detailed information about the:

  • RPLs
  • site characteristics and surroundings including ground and groundwater conditions
  • parameters you will need to use in risk estimation models to derive SSAC

Use the information you collected so far in your RA. If you did not do a GQRA you must also see the information requirements for a GQRA.

For DQRA, the range of information you need will be broader and more detailed. For example, you may need to:

  • expand your site investigation and monitoring to ascertain plume migration
  • find out more detailed information on contaminant breakdown products
  • get detailed information on hydrogeological properties such as hydraulic conductivity, direction of flow and effective porosity
  • collect data to confirm the presence or absence of a pathway
  • get site-specific parameters to use in the RA model - such as fraction organic carbon and half-lives for degradation
  • collect site-specific information relating directly to the effect of the contaminants on the receptor such as further soil testing, sampling of home grown produce or monitoring of indoor air quality

You may also need additional information on the nature of the contaminant, the soil and water matrix.

The nature of the contaminant includes:

  • chemical type for example, organic, inorganic, ionic
  • toxicity
  • concentration, amount and distribution - laterally and vertically
  • solid, liquid or gas
  • solubility, volatility, density
  • biodegradation potential
  • partitioning behaviour of soil, sediment, water, air or biological factors
  • contaminant transport properties including evidence of degradation

The nature of the soil and water matrix includes:

  • physical form and properties - such as particle size
  • lateral and vertical distribution of contaminants
  • gas and liquid permeability such as diffusion and preferential pathways
  • chemical composition - such as pH, organic matter content, other pollutants, including inhibitors
  • physical and chemical stability

You must use appropriate sampling and analysis procedures. This includes appropriate methods to preserve and transport samples from the site to the laboratory.

You must use MCERTS.

Collect DQRA site investigation information

For a DQRA, you will need to design and carry out an appropriate intrusive site investigation. You may need to phase this for complex sites.

You must consider the practicability, costs, effectiveness and benefits of site investigation.

If it’s not practicable or cost effective to collect all the information you may need to go back and review the overall site objectives.

The information you collect must be relevant, sufficient, reliable and transparent.

If you’ve previously done a site investigation as part of a GQRA then you can build in any additional information to:

  • address uncertainty and data gaps - for example, the need for additional samples in a specific area or at a specific depth
  • collect additional data to confirm RPLs

You will need to produce a site investigation report or present the results in your DQRA report.

Confirm the RPLs to be assessed

Use the site investigation information you’ve collected to confirm which RPLs need to be assessed. You may:

  • be able to rule out some of the potential pollutant linkages from the PRA or RPLs from your GQRA
  • need to add some new RPLs

You must also check if there are any changes in site circumstances that might affect which RPLs need to be assessed.

If you conclude that you have insufficient information to confirm or rule out pollutant linkages then you may:

You must update the CM with your findings and record these decisions.

Assess the risks

To assess the risks you can either:

  • derive SSAC
  • get detailed information about the receptor

Derive SSAC

SSAC are values for concentrations of contaminants derived using risk estimation models such as CLEA or RTM. They’re based on detailed site specific information about the characteristics and behaviour of contaminants.

SSACs will correspond to how you will evaluate the risks for the site.

To derive SSACs you will need detailed site-specific information on all of the following:

  • characteristics and behaviour of contaminants
  • pathways
  • receptors

Collect information about the receptor

For DQRA, you do not always need to derive SSAC or use a risk estimation tool.

You may be able to collect additional information to fill in any gaps to confirm an RPL. For example, this might include collecting site-specific information on land use or sampling home-grown produce to decide whether there is an unacceptable risk.

If there is an unacceptable risk then you can use this additional information to develop remediation criteria in tier 1 of OA.

If you are dealing with ecological receptors you can find detailed information on the CL:AIRE WALL - see assessing risks to ecosystems (INFO-RA2-5).

Select a DQRA risk estimate tool

If you select a DQRA tool it must relate to the type of receptor you’re dealing with.

We expect that risk assessments for pollution of controlled waters are done in line with the tiered framework set out in the:

The models you use for DQRA will need detailed site-specific information as input parameters.

You must check the model’s sensitivity to any particular assumptions. You will also need to evaluate the uncertainties to ensure that the SSACs are sufficiently precautionary and conservative.

You can use some of these DQRA tools to derive SSAC, if it’s appropriate to do so.

Decide if there are unacceptable risks

You must consider:

  • how much any exceedance matters and how it relates to how you’ll evaluate the risk - this may need agreement from the regulator
  • if concentrations are representative of background conditions
  • if any assumptions used are representative of the site
  • any uncertainties within the DQRA
  • any additional evidence that has been collected to support interpretation

You must understand the sensitivity of the SSAC. You will also need to evaluate any uncertainties to ensure that the SSACs are as representative as possible for the actual site conditions.

You must justify how you have evaluated the risks and include this information in your DQRA report.

Conclude DQRA

At the end of this tier you will need to create a decision record. This must include the:

  • pollutant linkages you’ve identified - explain how you further developed the CM for example with site investigation results
  • criteria, tools and assumptions you used or developed to estimate the risk
  • potential risks - unacceptable or acceptable - and how you evaluated them
  • justification for your proposed next steps

Update the CM with confirmed RPLs.

You must decide if:

  • the unacceptable risks have been dealt with, no further action is required and you can exit the process
  • more information is needed to address uncertainties and complete the DQRA - for example, further assessment, site investigation and monitoring
  • there’s unacceptable risk and you need to move to OA

Your decision may need approval or agreement from the relevant regulator - for example, approval of a Part 2A obligation or to satisfy a planning condition.

Produce a DQRA report

You need to produce a:

You must submit your DQRA risk estimation tool to the regulator if applicable.

You may decide to use the NQMS.