In addition to complying with the requirements of Iowa’s “One Call” system, before the start date of any PROW excavation, each registrant who has facilities or equipment in the area to be excavated shall mark the horizontal and approximate vertical placement of all said facilities. Any registrant whose facilities are less than twenty (20) inches below a concrete or asphalt surface shall notify and work closely with the excavation contractor to establish the exact location of its facilities and the best procedure for excavation.