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.

Variability in UK Laboratory Methods for the Identification and Quantification of Asbestos in Soil

Issue Date: February 2021

SoBRA’s asbestos sub-group surveyed UK laboratory methods for the identification and quantification of asbestos in soil back in 2018-2019. With the withdrawal of the Standing Committee of Analysts (SCA) Blue Book method for the quantification of asbestos in soil last year this paper should help in understanding some of the key differences in the methods used by laboratories, and it also makes recommendations for how asbestos results should be reported to best inform subsequent risk assessment.

Guidelines for Airborne Concentrations of Asbestos Fibres in Ambient Air: Implications for Quantitative Risk Assessment

Issue Date: January 2021

SoBRA is pleased to announce the publication of further work by its Asbestos Sub-Group. Since a workshop held in April 2019 the sub-group has been working on revision to the discussion white paper published in 2017 on air quality guidelines for asbestos. A key action from that workshop in 2019 was to evaluate the use the linear as well as the non-linear versions of the risk algorithms published by Hodgson & Darnton in 2000. It was the view of the participants of the workshop that the linear model for pleural mesothelioma might be more appropriate for the calculation of risk from low environmental exposures compared to the higher occupational exposures that were the primary focus of the Hodgson & Darnton paper. The updated SoBRA paper presents a comparison of risk models, including the new application of the Hodgson & Darnton algorithms. A beta version of an Excel-based spreadsheet (Jan 2024) has been developed to support the updated paper, allowing users to select from the algorithm options presented in the Hodgson & Darnton (2000) paper and the Darnton (2003) paper, and therefore enabling users to perform model choice sensitivity analysis and evaluate the difference the use of alternative algorithms makes to estimated risk. It is hoped that the updated paper and supporting Excel tool help further our understanding of potential health risk associated with exposure to airborne asbestos.

Feedback is welcomed – please submit to [email protected]

The Distribution of Asbestos in Soil – what can the data mining of sample results held by UK laboratories tell us?

Issue Date: March 2020

This discussion paper is a continuation of the series of discussion papers that the SoBRA asbestos sub-group has published since 2015.   In 2013, SoBRA identified a number of research gaps that had direct relevance to the risk management of asbestos in soil. One of these was the lack of a collective understanding on what typical background concentrations of asbestos in soil across the UK were. To provide a complementary line of evidence to Defra’s recently published Research Project SP1014 (Establishment of typical background levels of dispersed asbestos fibres in urban and rural soils in England and Wales), SoBRA issued a request to major UK soil laboratories to provide SoBRA with anonymised asbestos in soil data.  The principal aim of this paper is to provide a factual presentation of the data provided by the laboratories. The information presented may be used by risk assessors and decision makers as a line of evidence as they see fit.