The investigative arm of Congress is looking into how federal agencies carried out a plan to clean up uranium contamination on the Navajo Nation.
About 4 million tons of uranium ore were mined from the reservation from 1944 to 1986, leaving a legacy of death and disease.
Federal agencies in 2008 began implementing a 5-year plan to address the contamination.
The U.S. Government Accountability Office recently spent time on the Navajo Nation to find out whether the goals were accomplished, what work remains and the key challenges.
The GAO plans to issue a report on the site visits in February.
The Navajo Environmental Protection Agency says a second 5-year plan that will cover 2013 to 2017 is being developed.