Water sampling and continuous ground gas monitoring

Water sampling and continuous ground gas monitoring

Project title:            Ground gas risk assessment at a proposed residential development site

Client:                        Large Engineering Consultant

Location:                  Village A, Oxfordshire

Start date:                February 2016

End date:                  March 2016


Services provided:

  • Continuous gas monitoring
  • Continuous water monitoring
  • Water sampling

Key benefits:

  • Saved time
  • Reliable data
  • Informed decisions


Water sampling and continuous ground gas monitoring


Ground Gas Solutions (GGS) was approached by a Large Engineering Consultant regarding a planned development of approximately 200 private residential properties in an area in Oxfordshire. The proposed site was historically a ‘greenfield’ space used for agricultural practices, however, a potentially significant pollutant linkage from two landfills situated to the east and south east of the area had been identified during a Phase 1 Preliminary Desk Study.

Although some gas management strategies were already in place to monitor the risk of lateral gas migration from the landfills towards the development site, further assessment was required to quantify ground-gas risk and undertake measurements of the high water levels present on site. GGS was therefore commissioned by the clientto carry out further investigation within an eight week window and report back with recommendations for the client.

Hea - 1

Water sampling of a borehole using a low flow bladder pump.

Existing pathways were discovered for ground-gas and dissolved gas migration from the landfill through shallow soils. In response to this, GGS planned and undertook high frequency continuous monitoring of groundwater levels and ground gases at selected locations along the site boundary. Dissolved gas sampling and analysis was also undertaken as groundwater is known to be a potential migratory pathway for methane and carbon dioxide.

During the first visit GGS began monitoring via four monitoring wells over a two week period. Two tennax tubes were deployed within two of the monitoring wells to confirm the presence of any volatile organic compounds (VOCs). On the return visit, water samples were taken from the four monitoring wells using a low-flow bladder pump and a multiparameter water quality probe. GGS carried out high quality work efficiently and within the limited time constraints.

It was concluded that methane remained below the limit of detection during the four-week continuous monitoring period of the eight monitoring wells, but there was presence of carbon dioxide and VOCs, however, they were below CIRIA guidance thresholds.

GGS produced a factual report offering a comprehensive summary of works carried out at the development site. It provided graphical representation of the ground-gas regime in all the monitoring wells. Also included were the results of ground-gas analysis, concentration duration analysis, groundwater sampling analysis and atmospheric pressure regime analysis.

Through the practice carried out GGS were able to offer a quick, cost effective solution to the ground-gas risk at the site, enabling the developer to make informed decisions regarding the safe construction of the future developments, as well as ensuring the properties and future users of the developments are protected from potentially harmful ground gas exposure.


This case study was written by Heather, a Graduate Geo – Environmental Specialist, at GGS. Heather studied a BSc in Earth and Environmental Science and an MSc in Energy and the Environment.

Find out more about the benefits of continuous gas monitoring here.