It is 20 years since Risk and Reliability in Gas Protection Design was published in Ground Engineering. The paper, written by EPG UK Technical Director Steve Wilson and Geoff Card of GB Card and Partners, underpins the risk assessment approach used in all subsequent guidance (CIRIA C665 and BS8485).

However, there is still an over emphasis by some on maximum gas concentrations recorded in monitoring wells, regardless that flow rates are consistently low or even not detected. Based on the wealth of research carried out by them since 1999 Steve and Geoff, along with James Lucas of Core Envronmental Projects (formerly EPG Australia) have written a paper that describes a new screening method to gas risk assessment based on a more analytical approach.

The paper is published in two parts in Ground Engineering magazine. The first published in August 2019 describes the background information, including research on the processes that affect gas generation and migration in natural soils such Alluvium. The second part describes the analysis used to develop the new screening values along with the values themselves.