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.

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.