There were seven spoil tips on the slopes above Aberfan; Tip 7—the one that slipped onto the village—was begun in 1958 and, at the time of the disaster, was high. In contravention of the NCB's official procedures, the tip was partly based on ground from which water springs emerged. After three weeks of heavy rain the tip was saturated and approximately of spoil slipped down the side of the hill and onto the Pantglas area of the village. The main building hit was the local junior school, where lessons had just begun; 5 teachers and 109 children were killed in the school.