52 Pa. Stat. § 690-275
The superintendent shall not permit the mining of coal in any seam the entire distance to a permit boundary, not including boundaries around reservations or along crop lines, when on the adjoining property there are mine workings in the seam within 3,000 feet of the permit boundary. A barrier pillar shall be left, from the operation to the permit boundary, of not less than ten feet plus two feet for every foot or part of a foot of thickness of the bed measured from the roof to the floor, plus five feet for each 100 feet or part of 100 feet of cover over the bed at the permit boundary. If the coal on one side of the permit boundary has been mined prior to the effective date of this section closer to the permit boundary than permitted, the barrier pillar to be left in the mine approaching the permit boundary shall be at least equal, when added to that already left in the adjoining mine, to that required on both sides of the permit boundary. If, in the opinion of the department or the superintendent of either mining property, the barrier pillar is deemed insufficient, after due notice to the operator of the adjoining mining property, one-half of the barrier pillar shall be left on each side of the permit boundary, except as provided in this section. The department, the superintendent or owner of either mining property shall determine the thickness necessary to afford safety and protection. If it is agreed by the department and superintendents of the adjoining coal mining properties that the permit boundary is so located that there is no danger to property or lives in mining coal on either or both sides of the permit boundary up to the permit boundary, then mining to the permit boundary shall be lawful if all danger from accumulated water and gas shall have first been removed by driving a passageway to tap and drain off any accumulations of water and gas, as provided for in this act.
52 P.S. § 690-275