Well this morning we hit a void at about 37.5m - possibly a cave in the relatively thin ('10 ft') Marlstone bed indicated in the geological maps - there was a harder region first. At all events this is a problem - all the drilling water flushes away rather than returning with the debris. If we had a fire hydrant amount of water available one might live with this (one thinks of that burst main..) but otherwise options are limited. Drilling 8*37.5m rather than 4*75m holes would be simplest - if there is enough room, which looks a bit tight. Experience apparently suggests that if one hole hits a void others around it are also likely to. Pic is of the drilling system running before hitting the void.
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