The Mainshaft flooding was a direct result of grouting methods and procedures which were inappropriate to site conditions. Grout holes were not flushed clean of drilling debris and mud infillings, nor was water pressure testing undertaken. The holes were grouted to full depth in one pass, rather than using a stage down drilling and grouting technique. Grout injection pressures were too high (1000 - 2000 psi) for the weak, highly-fractured ground conditions.
The use of excessive grouting pressures further weakened the rock formation adjacent to the shaft and caused the shaft bottom to blow out. Seawater entered the shaft and rose at the rate of 12 m per hour until the shaft had filled to sea level. Recovery efforts were attempted for the following three months and consisted of drilling and grouting along the shoreline adjacent to the Mainshaft, as well as dewatering
two adjacent shallow shafts. These operations were virtually shots-in-the-dark and did not have any effect on the water inflow at the shaft bottom.