Ahead of Brownfield Land Wales 2019 (3 October, Cardiff), we’ve put a few questions to Steve Wilson, Technical Director, The Environmental Protection Group Ltd who will be speaking on the practicalities of continuous monitoring for cost-effectively assessing the risks from ground gases and soil vapours at the conference.
Q. What do delegates need to know about the current guidance for ground gas and vapour risk assessment on development sites?
A. The most important thing to note is that BS8485 was updated in 2019 so risk assessors and gas protection designers should be aware of this. There is also a new risk assessment approach that has been published in Ground Engineering this year that will help transform the way gas risk assessment is completed. There are webinars that can be downloaded from the LQM website that explain how to apply BS8485 correctly and also several Ground Gas Information Sheets on the EPG website that explain how to address various issues in ground gas assessment
(epg-ltd.co.uk). CL:AIRE has a number of new documents about ground gas on its website.
Q. How much has guidance changed in the UK and internationally in recent years and why is this?
A. One of the main changes in the guidance is that we now understand that high concentrations of gas do not necessarily pose a risk to developments. It is possible to have quite high concentrations of methane (up to 30%) and carbon dioxide (up to 21%) in the ground that do not pose any risk to overlying developments. There is also more advice on interpretation of continuous gas monitoring data.
Q. What is the regulator’s perspective on new monitoring technologies (in general)?
A. Regulators have been very receptive to new monitoring technology, especially continuous flow rate monitoring, both in the UK and elsewhere around the world.
Q. Which methods and technologies provide continuous monitoring of ground gases and soil vapours without breaking the bank?
A. The most appropriate gas monitoring method should be used on any site. In some cases spot monitoring is fine and in others continuous monitoring will provide benefits by allowing the scope of gas protection to be reduced (or even completely removed). The same also applies to vapour monitoring, at EPG we normally specify canister sampling where VOC analysis is required but there are alternative technologies. Every method has its pros and cons and it is down to the risk assessor to justify why they have specified a particular method.
Q. Would you mind giving us a real-world example of best practice in ground gas and VOC risk assessments and tell us what makes this approach so effective?
A. At EPG we base all our assessments on the CSM. We use the gas monitoring data from Ambisense Gasflux units (with continuous flow data and also weather data) along with Ambilytics, which involves data science methods, to show relationships and to help us understand the processes that are causing elevated gas concentrations in the ground. Once we understand that we are quite often able to remove the need for any gas protection in developments which can save developers hundreds of thousands of pounds and in the end is more sustainable that installing plastic gas membranes everywhere. We have recently used this approach to demonstrate that carbon dioxide from a site in a mine working area was from natural processes in shallow soil (as was depleted oxygen) and that there was minimal risk of mine gas emissions.
Steve will be going into further detail on these topics at the Brownfield Land Wales conference on 3rd October 2019 in Cardiff. Find out more here.