Mining regions that have had extensive activity, such as the Appalachian coal fields in the U.S., have incomplete archives and cannot accurately specify the location of old mine workings. In this region, auger mining, or drift mining from outcrops has been extensive and modern mining operations must navigate away from these potentially water-filled workings. MSHA guidelines (30 CFR 75.388) require that mines developing near old works drill at frequent intervals from developments to ensure that the new workings are driven sufficiently away from the abandoned ones. As an alternative to traditional fan-pattern drilling, REI uses directional holes to verify reserves and the extent of old works well in advance. Drilling can be performed from underground, from the surface, or from seam-to-seam.