What is periodic monitoring?
At it's simplest, periodic monitoring is the measurement of key ground gases at set intervals from a borehole-based gas monitoring well.
Using specialist handheld equipment, we measure borehole flow rates and gas concentrations every minute over a 10 minute period or until conditions stabilise. We do this to ensure we get a representative measurement of the well conditions, rather than an unrepresentative instantaneous values.
Usually, periodic monitoring will be repeated at a site multiple times over a period of time. That period can range from weeks to months, or even years. The monitoring period and frequency of visits depends on the perceived gas hazard and the sensitivity of the proposed development.
What is it useful for?
We use periodic monitoring alongside continuous ground gas monitoring to generate additional lines of evidence to help inform ground gas risk assessment. This is often associated with proposed site developments, but also to monitor and assess sites with existing uses.
Periodic monitoring of ground gas concentrations from a well can reveal a lot of relevant information about the ground gas regime at your site. It can also tell you about the condition and effectiveness of your monitoring infrastructure and about the geology of your site.
But there are pitfalls too. A poorly installed or maintained well can lead to misleading results. So, you need a competent, experienced surveyor to carry out and analyse this type of monitoring.
And here's an example
At this site the periodic monitoring is showing elevated carbon dioxide coupled with depleted oxygen
What are the benefits?
While an inexpensive technique to use, periodic monitoring can add real value to any ground gas investigation, provided it is executed competently and reported accurately.
It's a technique best used in conjunction with continuous ground gas monitoring to build a comprehensive and robust evidence base to inform risk assessments. Periodic monitoring provides an really valuable opportunity to validate your results and check on the condition of your monitoring wells.
Want to know more? Then feel free to get in touch.