Drilling muds are often recovered, treated, and reused in other wells, especially if getting the mud to and from different well sites is convenient, as on a multi-well pad. Compressed air, rather than drilling muds, can be advantageous when there are few “water zones” (rock formations that are saturated with water) between the groundwater and the target formation, or when drilling muds can damage shale. Shale can be damaged if it absorbs the water from drilling muds, sloughs off, and clogs the bottom of the well bore; shale can also lose permeability if drilling muds are forced into spaces around the wellbore. Compressed air drilling is a common practice in New York State.