The petitioners' main contention was that one restriction imposed by the DER is that "50% of the coal beneath structures protected by § 4" must be left unearthed to support the surface land, and that consequently their "support estate had been entirely destroyed" because they had to leave 50% of the coal beneath the surface in place, so they could only mine the mineral estate while leaving the support estate untouched. In answers to interrogatories, the petitioners claimed that from 1966 to 1982 their land use rights at their 13 coal mines had been restricted to the point of a taking because of the Subsidence Act. As a result, they claimed that they had to leave about 27 million tons of coal in place. Altogether, these mines contained at least 1.46 billion tons of coal. The percentage of coal that had to remain unmined was less than 2% of the petitioners' total coal.