Closeup of a washout zone in a mudstone layer just below the Culebra Dolomite in the Waste Shaft. Part of a cavernous area is visible, 6.7 feet from top to bottom and extending 2.5 feet into the shaft wall. (In the presence of circulating groundwater, salt (halite) is converted into mudstone.) Shaft construction resulted in deep washouts that required the installation of 10-foot steel liner plates to prevent further caving in of the shaft walls. Water seeps into the shaft at this level. (Photo from EEG 32: The Rustler Formation as a Transport Medium for Contaminated Groundwater)