225 ILCS 705/34.04
During pillar recovery in any mine when working places approach within 50 feet of abandoned sealed workings, as shown by surveys made and certified by a competent engineer or surveyor, which may contain dangerous accumulations of water or gas, or within 200 feet of any workings of an adjacent mine, boreholes shall be drilled to a distance of at least 20 feet in advance of the face of such working place. Such boreholes shall be drilled sufficiently close to each other to insure that the advancing face will not accidentally hole through into such workings. Boreholes shall also be drilled not more than 8 feet apart in the rib of such working place to a distance of at least 20 feet and at an angle of 45 degrees. Such rib holes shall be drilled in one or both ribs of such working place as may be necessary for adequate protection of persons working in such place. The above provisions shall apply to any working place in any mine at any time should conditions warrant same in the interest of safety.
225 ILCS 705/34.04