The Society of Brownfield Risk Assessment (SoBRA) has recently issued the LNAPL Mobility Screening Tool. 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. They are available to download free of charge here.
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, it provides 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.