Numerical modeling of groundwater flow in the Navajo sandstone aquifer at the Tuba city, Arizona, disposal site - 15167

A numerical model is being developed to describe groundwater flow in the Navajo Sandstone aquifer that underlies the US DOE Office of Legacy Management Tuba City disposal site that is located near Tuba City, Arizona. The site is a former uranium-ore processing mill that operated from 1956 until 1966. Resulting groundwater contamination extends approximately 457 meters (1,500 feet) off the site. The primary contaminants are nitrate, sulfate, and uranium. Onsite solid waste encapsulation was completed by 1990 and pump-and-treat groundwater remediation was implemented in 2002. A site conceptual model, along with an approach to numerically simulate groundwater flow and advective transport of contaminants at the site, is being developed. Numerical model calibration will address transient periods of active and inactive groundwater withdrawal during the remedial action. The calibrated model will be applied to forecast contaminant capture under the current and hypothetical groundwater extraction scenarios. (authors)