Improved ground-gas risk prediction using In-borehole gas monitoring.

UoM administered thesis: Phd

  • Authors:
  • Arthur Nwachukwu

Abstract

Elevated concentrations of ground-gases (CH4 and CO2) and VOCs in contaminated soil and water around the world pose significant risk both to human health and the environment. There is, therefore, a requirement to monitor them for effective risk assessment and remediation. Current ground-gas monitoring is often ineffective for determining their representative concentrations and fluxes - the two most important parameters necessary for ground-gas risk assessment. These failures of current monitoring may arise from its low temporal resolution. The recent ability to monitor at high temporal resolution - using Gasclam - makes it possible to determine whether this is the case and whether high resolution monitoring can be more effective.CH4 and CO2 were monitored at several sites using Gasclam. This showed that in many cases concentrations were sufficiently variable that current sampling practices would be ineffective at detecting worst case concentrations. Furthermore, the time-series data produced by Gasclam allowed the predictive power of the established relationships between atmospheric pressure and gas concentration to be improved. The failures in the relationship could also be understood as hysteresis which gave an index of ground permeability and/or gas generation. These improvements in understanding could be used to improve the conceptual site models on which risk assessments are based.Similarly, high temporal resolution VOC measurement demonstrated the need for such measurement. The factors controlling VOC concentration were shown to be same to those controlling ground-gases; again this understanding of process would also improve the conceptual site model. A monitoring method that incorporated parallel non-specific real time measurement with a time integrated VOC measurement that identified specific VOC's was tested. The method was an improvement on the separate methods as it could be used to reasonably infer the concentrations of specific VOC's at high temporal resolution.The ability to monitor gas concentrations at high temporal resolution gave the potential for the rate of gas concentration recovery subsequent to purging of the borehole to be used as an index of gas flux. These tests proved to be practical, generally taking less than the time of a site visit, and reproducible. Variability in these recovery profiles was assessed at different sites, times and for different gases.

Details

Original languageEnglish
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Award date31 Dec 2014