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.

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

Petroleum Hydrocarbons Workshop Report (SoBRA 2013)

SoBRA held a workshop on assessing risks to groundwater from petroleum hydrocarbons in June 2012. The workshop included discussion groups on four key themes: site investigation and sampling; laboratory analysis and environmental forensics; groundwater risk assessment modelling and development of guidance; and assessment of the vapour risk from groundwater. Proceedings and presentation slides from the workshop are available free to members.