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Why Measuring Water Levels is Crucial for Understanding Ground Gas Behaviour

Steve Wilson

Ground gas measurements are influenced by a myriad of factors – the underlying gassing activity, subsurface migration conditions, meteorological and tidal factors, and the status of the monitoring well itself. Here’s Why Measuring Water Levels is Crucial for Understanding Ground-Gas Behaviour:

Testing the Waters is Critical

As surely as the weather invariably permeates our social conversations, weather conditions also affect each of these influences:

  • the underlying gassing activity
  • subsurface migration conditions
  • meteorological and tidal factors, and
  • the status of the monitoring well itself.

Water penetration and saturation in the soil is critical to microbial or leaching conditions that produce gases; lateral water movement will drive or inhibit gas fluxing behaviour through the ground; water ingress/egress in monitoring wells will change the void head-space volume, producing pressure differentials which will affect the gas composition and may induce flows by a piston effect.

Even more detrimentally, the monitoring wells may become swamped such that the perforated sections are below the water level, hence rendering the monitoring well as non-representative due to gases measured being those of a stagnant head-space.

Furthermore, elevated water levels are conducive to gas dissolution and evaporation, introducing further uncertainty in the gas head-space measurements given the omission of gas levels dissolved in the ground-water.

Why Measure Water Levels

Measuring water levels in the monitoring wells add a dimension to the site assessment which sheds light on these influences on ground-gas. Therefore fluctuating gas levels and flow conditions can be considered with respect to water levels within the well, attributing causality to the gas behaviour regime.

However, at Ambisense, we go beyond this; further delving into the factors leading to the water levels, contextualising them with respect to

  • precipitation rates,
  • barometric fluctuations and
  • tidal height variations.

In this way, the representativeness of the gas measure can be confirmed – better again, it can be confirmed in near real-time, allowing corrective actions to be taken as necessary – pumping out or recommissioning a swamped well, investigate water (typically aligned with gas) migration pathways and rapid diagnosis of gas measurements with respect to internal (i.e. organic off-gassing) or external (e.g. weather) conditions.

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