SEPA recently published the long awaited revised guidance WAT-PS-10-02 on 'Assigning Groundwater Assessment Criteria for Pollutant Inputs'. They also published an associated 'List of Groundwater Standards' and updated their guidance on 'Land Contamination and Impacts on the Water Environment' (commonly referred to as the 'Brown Booklet').
The revised SEPA guidance reflects the new Status and Standards Directions and came into force on 1st February 2025. All the new documents can be found on the SEPA website where you will find guidance on the use of the standards at existing sites and information about the transition period that runs until 1 July 2025.
SCLF Webinar
SCLF held an extended webinar on 27 February 2025 to raise awareness of the new guidance and included 3 presentations:
Protecting Scotland's Groundwater from Pollution | Isla Smail, SEPA
Risk Assessment Implications of the New Guidance - An industry perspective | Helen McMillan, RSK Geosciences
Considerations for Site Characterisation | Alison McKay, Leapmoor LLP
The webinar was definitely a popular one and there was a lot to get through and so we recommend that you consult the full revised guidance as we haven’t covered everything! The attendees raised many questions during the webinar and these have now been summarised into a frequently asked questions (FAQ) list to accompany the webinar recording which is now available on the SCLF YouTube channel.
It should also be noted that the information in the webinar and this FAQ relate to the approach taken to assessing risks to groundwater in Scotland only. A different approach applies to the rest of the UK.
Frequently Asked Questions
All the answers provided in this FAQ are the presenters’ opinions, which are provided for information only and do not constitute formal SEPA guidance nor consultancy advice.
We will be adding to this list so if you have any questions after watching the webinar and reading the guidance then put them in the comments.
Question: Is the approach for assessing risk to groundwater from the input of hazardous substances leached from Made Ground the same under Part IIA and the planning regime (in terms of assessment/ compliance point and what is considered an unacceptable risk)?
Answer: The criteria for Planning and Part IIA are different. See section 5.2 of our guidance on ‘Land contamination and impacts of the water environment’ for more details. The acceptability of risks will depend on the hydrogeological context and the relevant regulatory regime.
Question: If you are unable to take into account background groundwater that is already contaminated, the potential exists for you to have to remediate somebody else's contamination which seems unfair.
Answer: There is no expectation of remediation of upgradient background water quality. However, it needs to be taken into account when assessing risks from additional inputs to groundwater. In addition, background concentrations may be taken into account if setting site-specific compliance criteria. Note that compliance criteria may differ from the default standards used in risk assessment on a site-specific or borehole-specific basis – further information on setting compliance criteria is presented in A1.5 of WAT-PS-10-02.
Question: To assess risk from your site only, you must have to ignore the background upgradient concentrations
Answer: Background concentrations are applicable to any considerations of potential dilution potential when assessing against pollution and status standards. The hazardous substance input standards are assessed immediately prior to the point of entry into groundwater and thus background concentrations do not need to be considered during the risk assessment. Background concentrations may be relevant if setting site-specific compliance criteria.
Question: You state that the new version of WAT-PS-10 doesn't apply to surface waters. So it is SEPA's intention that we continue to use the previous version for assessing risks to these receptors?
Answer: WAT-PS-10-02 applies to assessing risks to surface waters via groundwater baseflow. It does not apply to other potential linkages to surface waters that do not involve groundwater e.g. surface run-off etc.
Question: With regard to the >50m/<50m proximity to surface waters for hazardous substances, would a culverted watercourse still be considered a surface water? Or does this require a different approach?
Answer: Yes it would still be considered as a potential surface water feature. However, in your conceptual site model (CSM) the likelihood of interaction between the groundwater and surface waters should be taken into account depending on the lining of the culvert and whether they are in hydraulic continuity.
Question: Is residual saturated zone non-aqueous phase liquid (NAPL) still considered to be ongoing or historical, or does this require site specific lines of evidence?
Answer: NAPL in the saturated zone and/or present as a measurable layer above the water table would normally be considered to pose a potential risk of ongoing entry into groundwater unless there is site-specific evidence to the contrary (note that this is a different approach from that taken by the Environment Agency). However, if the NAPL contamination was due to historical activities, then you can also consider pollution and status tests during your risk assessment. If historical NAPL, then you could also potentially take disproportionate cost exemption when considering the potential remedial strategy.
Question: How do you define if hazardous substances have already entered groundwater? does this take into account background concentrations off site, and must there be a plume of contamination on site and not isolated spikes in only certain boreholes on site (for hazardous substances to be considered to have already entered groundwater)?
Answer: There does not necessarily need to be a defined dissolved-phase plume for entry of hazardous substances to groundwater to be occurring. Note that entry is assessed at the base of the unsaturated zone prior to dilution. If the contaminant of concern is being identified in the groundwater, then entry is probably occurring unless there is evidence to the contrary. Elevated background concentrations may make interpretation of groundwater data more complex and other lines of evidence should be taken into account.
Question: For hazardous substances isn't assessing risk and setting of compliance criteria essentially the same thing?
Answer: Risk assessment criteria and compliance criteria are different. Risk assessment criteria are used in assessing whether there is a risk to the water environment. The risk is assessed at an assessment point - in the case of hazardous substances this would be the base of the unsaturated zone prior to discharge into groundwater. The compliance point is something you can physically measure e.g. groundwater. Compliance criteria are used in assessing operational performance and can take into account other factors such as background water quality, LoD or agreed exemptions. Annex 1.5 of the guidance provides some more detail.
Question: A comment more than a question: when using a 1.5D approach (source width x plume length from Remedial Targets Methodology (RTM)), need to be careful as RTM include lateral dispersion which would make plume modelled larger than source. Can be set as zero.
Answer: Agreed that this is something that will require consideration when interpreting modelling results, particularly if the model results are very close to the standard. In practice, lateral dispersion is often of secondary importance when it comes to plume geometry.
Question: Are we saying that no matter how contaminated a plume is, as long as the total area is less than the spatial test, then we don't have an issue for Future Groundwater Resource?
Answer: If the threshold value is not exceeded over a 1Ha area, then it would not be considered to cause a pollution risk to future groundwater resource potential. It is also important to consider the expected maximum plume extent and whether there is ongoing entry.
Question: Is it the case that more time and effort needs to be spent at the Preliminary Risk Assessment (PRA) stage? Not only that but that this should be completed and submitted to the regulators in advance of the site investigation (SI) being scoped and where possible at the pre-planning stage?
Answer: A preliminary investigation is an essential first step in site investigation and assessment (See BS10175). The output of this stage is the initial conceptual site model and PRA, both of which are prerequisites for robust site characterisation and subsequent risk assessments. Whether pre-app discussions are likely to be appropriate will depend on the regulatory regime and the complexity of the site. It is not required by default.
Question: What in practice are we really going to use as an 'annual average' from spot soil leachate data for example in realistic industry SI norms?
Answer: If you only have limited spot soil leaching data, then there is no expectation of temporally averaging. However, annual averaging might be relevant to take into account in the conceptual site model or in numerical modelling in terms of seasonal variations in depth to water table or recharge, etc.
Question: Some of the new standards for some of the total petroleum hydrocarbon (TPH) fractions are exceptionally low compared to lab limits of detection (LODs). e.g. 0.0015ug/l for ALI EC >16-35. How do you work with that?
Answer: Different approaches are required for characterisation, risk assessment and compliance. See Section A2.4 of WAT-PS-10-02 for more details.
Question: Is there an intent to issue guidance on the cost benefit analysis aspect for exemptions?
Answer: SEPA are not planning to issue additional guidance on this in the short-term as it is dependent on both site-specific and time-variant factors. Note there is no change to the legal basis for the disproportionate cost exemption.
Comentarios