New boreholes into old gallery: Unterschied zwischen den Versionen
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| − | In the old days | + | In the old days closed mines were without degassing devices. Therefore, new access have to be created now in order to extract the gas in a controlled way. |
[[Bild:Borehole_abandoned-mine.jpg | Drilling into an abandoned mine ]] | [[Bild:Borehole_abandoned-mine.jpg | Drilling into an abandoned mine ]] | ||
