The Source of Groundwater and Solutes to Many Devils Wash at a Former Uranium Mill Site in Shiprock, New Mexico

The Shiprock Disposal Site is the location of the former Navajo Mill, a uranium ore-processing facility, located on a terrace overlooking the San Juan River in the town of Shiprock, New Mexico.The milling operations, conducted at the site from 1954 to 1968, created radioactive tailings and constituents of concern that are now found in the groundwater beneath the Mill. Elevated concentrations of constituents of concern have also been measured in groundwater seeps in the nearby Many Devils Wash arroyo, leading to the inference that these constituents originated from the Mill. The objective of this study is to increase understanding of the source of water and solutes to the groundwater beneath Many Devils Wash and to establish the background concentrations for groundwater that is in contact with the Mancos Shale at the site. Based on observations and data collected during this study, the likely source of groundwater beneath the Many Devils Wash arroyo was focused recharge of local precipitation and the source of solutes in the groundwater beneath Many Devil Wash arroyo is likely due to the weathering of the underlying Mancos Shale bedrock.