Soil and near surface gas monitoring in the Vale of Pickering

BGS is monitoring soil and near surface gas monitoring at locations in the Vale of Pickering. Concentrations of carbon dioxide (CO2), methane (CH4), oxygen (O2), hydrogen sulphide (H2S) and radon (Rn) are being measured in the soil, along with flux (the rate at which the gas is coming out of the ground) of CO2 and CH4. These measurements provide baseline data collected prior to any shale gas related operations in the area.

The baseline monitoring is similar to that carried out in Lancashire, with the potential to utilise other gas monitoring tools. Near surface atmospheric gases (CO2 and CH4) may be measured using laser gas analysers mounted on a quad bike or similar all-terrain vehicle. This makes continuous measurements as the vehicle is driven across the fields. Continuous monitoring of gas concentrations and fluxes are also planned at a small number of sites.

Background

For many years we have been analysing soil gases and the air overlying the surface in relation to geological CO2 storage. The techniques used have proved highly successful for measuring baseline gas concentrations, locating and studying rates of gas escape from natural vents, and demonstrating the absence of leakage from storage projects. The methods are equally applicable to baseline and production monitoring of shale gas operations. There is a time-limited opportunity to gather baseline data, which should allow existing natural or man-made sources of gas to be distinguished from any emission resulting from shale gas operations.

Gas measurements

As part of our monitoring activities we have carried out sampling of near surface gases in the Vale of Pickering in areas close to where planning applications were submitted for the development of shale gas (KM8). This has included measuring soil gas concentrations and the flux from the soil to the atmosphere.

Soil gas was monitored by hammering a small diameter steel tube into the ground to a depth of up to 1 m. Samples of the gas were then pumped to a portable field gas analysing instrument or collected for laboratory analysis. The steel tube was then removed from the ground. Flux was determined by placing a small metal chamber onto the ground surface and measuring the flow of the gas into the chamber. Both soil gas and flux measurements only took a few minutes and caused very little disturbance to the soil or vegetation. The photos below show each of the methods.


Soil gas measurement
gas flux measurement


A total of 142 sample sites were measured for flux in November 2015 but soil gas could only be determined at 100 of these because of wet ground conditions. Repeat flux measurements were made at 21 sites in March 2016 but waterlogged ground prevented further work.

Vale of Pickering soil gas monitoring area ringed in red. Map shows the superficial geology, which mostly consists of former lake deposits and glacial material (diamicton) sitting on Kimmeridge Clay Formation bedrock

Preliminary results for CO<sub>2</sub> flux from the soil in the Vale of Pickering, November 2015

Preliminary results for CO<sub>2</sub> concentrations in soil gas in the Vale of Pickering, November 2015

Comparison of CO<sub>2</sub> flux at the same sites measured in November 2015 and March 2016. Values were appreciably lower in March 2016. This is likely to be because of reduced biological activity and wetter soil conditions

Contact

Contact BGS enquiries for further information.