Conceptualising & Characterising Contaminant Distribution in Soil Top Tips

Issue Date: November 2023

The CL:AIRE “Professional Guidance:  Comparing Soil Contamination Data with a Critical Concentration” publication (v 1.1 February 2021) emphasised the importance of developing, refining and thoroughly understanding the Conceptual Site Model (CSM) prior to considering whether statistical analysis would be applicable for a soil contaminant data set.

In response to this publication, SoBRA set up a sub-group in 2022 with the intention of providing technical guidance to support risk assessment practitioners to understand the soil contaminant element of the CSM prior to carrying out any generic or detailed quantitative risk assessment (and any associated statistical analysis).  The guidance provides a series of tips on the key data sources that should be considered and the questions that should be answered by risk assessment practitioners, to ensure that the soil contaminant distribution is correctly interpreted, not only in the context of its chemical properties and the environmental setting, but also how the distribution and CSM may change over time through human and environmental influences.

LNAPL Mobility Screening Tool

Issue Date: July 2023

The aim of this tool and accompanying document is to provide guidance on interpreting how mobile LNAPL plumes are; as part of a lines of evidence approach to characterising LNAPL plume behaviour.

The tool provides commentary and an easily accessible set of spreadsheets containing the equations provided in the CL:AIRE 2014 publication An Illustrated Handbook of LNAPL Transport and Fate in the Subsurface. 
The included equations estimate:

  • the depth of LNAPL penetration below the water table;
  • the critical thickness of LNAPL in a borehole which will indicate lateral migration;
  • Darcy flux;
  • LNAPL hydraulic conductivity; and,
  • lateral LNAPL velocity.

The document discusses which parameters the mobility equations are most sensitive to,  sources of uncertainty; and provides guidance on where to obtain suitable values for use in the equations. In addition, for selected LNAPL and sediment types, we provide example input data and graphical output to estimate the depth of LNAPL penetration below the water table; and the critical thickness of LNAPL in a borehole.

28 July 2023: Version 1.1 of this document has been published.
Corrigendum: Changes are listed on the Revisions page of the main document for Box 3, Box 5 and Appendix 2 in the main document, and Appendix 3 (capillary height spreadsheet). Capillary height calculations made using Version 1 of Appendix 3 will be correct, however, please note that capillary height calculations made using the equation in Box 5 of Version 1.0 independently of the spreadsheet tool will be incorrect by a factor of 100.

Effective Solubility Tool

Issue Date: July 2023

Calculating the effective solubility of dissolved phase contaminants is an important step in evaluating and risk assessing groundwater concentrations on sites with NAPL sources. The aim of the Effective Solubility Tool and accompanying documents is to provide a peer reviewed spreadsheet tool and guidance on how to calculate and assess dissolved phase effective solubility limits for a range of hydrocarbon contaminants where these derive from NAPL sources.
The tool has been produced based on equations published in a variety of recognised technical guidance (e.g. CL:AIRE 2014, LNAPL handbook) and features:

  • a description of the methodologies and parameters used in the calculations;
  • a NAPL molecular weight calculator;
  • an Effective Solubility calculator based on ”TPHCWG” carbon banding;
  • an Effective Solubility calculator using the “Top 20” compounds present in a mixed NAPL;
  • an example library of published fuel compositions and real composition analysis of a range of NAPL types collated from the SoBRA contributors;
  • a library of organic compounds and their physical properties used in the calculations.

The document provides guidance on when and how to use effective solubility calculation in groundwater risk assessments and provides some worked example calculations.

The Climate Emergency: Practical Considerations in Brownfield Risk Assessment

SoBRA held a one-day workshop in Birmingham in June 2022 entitled ‘The Climate Emergency: Practical Considerations in Brownfield Risk Assessment’.  Risk assessment is a fundamentally important component of a multi-disciplinary approach to successful brownfield regeneration, and therefore, the adoption and integration of climate change considerations in brownfield risk assessment is critical.  

The aim of the workshop was to discuss how we may need to adjust our approach to brownfield risk assessment to account for actual or anticipated climate change and its effects on contaminant sources, pathways and receptors.  This report presents a written record of the discussions held during the Summer 2022 workshop.

Hazardous Ground Gas Top Tips

Issue Date: June 2023

Announcing the publication of the first document from the Ground Gases sub-group.

In 2020, SoBRA created the ground gases sub-group to support technical excellence in the assessment, estimation and evaluation of risks associated with ground gas.

The SoBRA Hazardous Ground Gas Top Tips document provides succinct, comprehensive guidance covering all aspects of assessing ground gas risk from desk study through to site investigation, monitoring, risk assessment and gas protection design.
This document aims to improve and encourage best practice to support practitioners when assessing the risks from ground gases.

Vapour Intrusion

Guidance Notes for Assessment in Contaminated Land Scenarios in the UK

Following the recommendations of the SoBRA Summer 2017 workshop and the publication of the SoBRA Groundwater Vapour Generic Assessment Criteria (GACgwvap), SoBRA has now published a series of accessible and concise practitioners’ guides to support informed decision making with respect to vapour intrusion (VI) risk assessment within the UK. It is acknowledged that there is already an extensive portfolio of existing industry guidance available both within the UK and internationally in relation to VI risk assessment, nevertheless, these practitioners’ guides aim to provide high level summaries of the existing guidance, covering key aspects of VI risk assessment and include signposting to the relevant published industry documents for more detailed information, where required.

The topics covered by the SoBRA practitioners’ guides published comprise:

1A. Conceptual site model development for assessment of VI contaminant linkages in the UK

1B. Benefits of soil vapour sampling for assessment of VI risks

1C. VI data collection considerations

Controlled Waters and Climate Change

Issue Date: August 2022

In 2021, SoBRA established a controlled waters and climate change subgroup to address the need to incorporate the effects of climate change into contaminated land risk assessments.

Climate change has the potential to significantly impact the predicted risks posed by land contamination in certain scenarios and whilst Cl:AIRE published a SUBR:IM bulletin on climate change, pollution linkages and brownfield regeneration back in 2007 there has not been any further published guidance for risk assessors in the UK on how to incorporate climate change considerations into controlled waters risk assessment over and above FAQ number 8 published in the Environment Agency’s Guiding Principles for Land Contamination (GPLC) Part 2 in 2010. SoBRA’s publication by the climate change and controlled waters sub-group sets out the current regulatory and guidance context, identifies current sources of authoritative information on climate change impacts for the UK, and sets out an approach for a qualitative appraisal of climate change impact at the Preliminary Risk Assessment stage, and a series of “What If” scenarios to be considered at GQRA. The report identifies the limitations that existing standard DQRA modelling software (such as RTM and ConSim) have when looking to model the short-term, transient nature of many climate change impacts, and recommends a series of steps to mitigate this in DQRAs.

Baildown Test Guidance for Light Non-Aqueous Phase Liquids

Issue Date: May 2022

Announcing the publication of the first document from the NAPL sub-group.

In 2019, SoBRA created a sub-group to support technical excellence in the assessment, estimation and evaluation of risks associated with non-aqueous phase liquid (NAPL) in the sub-surface. The sub-group has undertaken to produce a series of documents that address a number of key issues facing practitioners when addressing risks from NAPL.

This document focussed on baildown tests. Baildown tests are commonly carried out in wells that contain light non-aqueous phase liquid (LNAPL) to investigate its mobility, which is an important consideration for risk assessment. This baildown test guidance document provides practical guidance to support UK industry in conducting baildown tests and interpreting baildown test results.