Compensation of CH4 emissions during tunneling works in Asturias: A proposal with benefits both for local councils and for the affected population

The appearance of methane during the excavation of tunnels through Carboniferous strata has always been a significantly frequent event. The occurrence of methane in tunnels poses a twofold problem. On the one hand, there are the associated hazards for the safety of personnel: methane is both an inflammable and an explosive gas. It therefore becomes very important to estimate the methane flow reaching the tunnel as it advances in order to minimize risks and the negative effects of methane-related incidents. A number of calculation methods have been developed to estimate methane emissions in these specific underground workings. At the same time, methane is a potent greenhouse gas, with environmentally harmful effects and a pollutant potential more than 20 times that of carbon dioxide. The immediate consequence is that the aforementioned calculations methods should enable methane emissions to be predicted and allow the environmental impact of these methane emissions into the atmosphere to be assessed using the values thus estimated. In the present paper, a research study into CH4 emissions in the Variante de Pajares tunnels has been used to estimate the equivalent emission of CO2 to the atmosphere. Some significant compensatory actions are accordingly proposed to mitigate the environmental effects of tunnels excavated through methane-prone coalbeds and to contribute to the sustainable development of the affected areas. The results obtained would apply directly to the strata where they have been validated; however, it is not difficult to extrapolate the proposed methodology to other coal basins and other tunnels in similar conditions.

► The pattern of CH4 emissions in the Variante de Pajares tunnels is described.
► The equivalent emission of CO2 to the atmosphere is then estimated.
► It is compared with other CO2 sources commonly appearing in tunnels.
► Compensatory actions are proposed to mitigate the methane environmental effects.
► These actions contribute to the sustainable development of the affected areas.