While the construction consortium BAM, Wayss & Freytag und SMET Boring NV were ambitious to start building a tunnel of 4 kilometres length below the Ems, the project was shut down. It appeared that waterproofing-gaskets in between the elements of the tunnel did not operate not function correctly and groundwater could not be stopped. By order of and in cooperation with SMET Boring NV we designed a modification, with took three weeks, 16 hours a day, work. first of all a plan was worked out and afterwards a monitoring of welding activities took place, to be sure, that all engineer standards were conformed – everything in close cooperation with our partner. Before the construction was put into operation, the welding activities were analysed non-destructively. The finalisation was achieved six months earlier than planned. Therefore, the three weeks of stagnancy were more than compensated.