Groundwater Compliance Action Plan meant to mitigate risk to human health and the environment
February 10, 2026
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Office of Legacy Management (LM) staff and the LM Support Partner recently updated Tribal offices on a Groundwater Compliance Action Plan (GCAP) that’s being developed for the former Monument Valley Processing Site in Arizona.
A GCAP documents the approach for demonstrating compliance with the groundwater standards in Title 40 Code of Federal Regulations Section 192. This includes developing a conceptual site model, defining groundwater protection standards, conducting a risk assessment, assessing corrective actions, and selecting a compliance strategy that is protective of public health and the environment.
The Jan. 14 meeting in Window Rock, Arizona, was to inform partners and stakeholders of the progress being made on the site’s GCAP. Monument Valley is one of 10 LM sites for which a GCAP is being developed or updated.
During the Cold War, uranium ore from nearby mines was processed at a mill in Monument Valley. Contaminants from the milling operation infiltrated subsurface soils and groundwater. LM and its Support Partner are evaluating data to assess potential groundwater remedies.
“We wanted to give a briefing and have a discussion with the Tribal offices regarding future actions at Monument Valley to make sure the accessible water there stays safe,” said LM Site Manager Joni Tallbull. “It’s important to keep the Tribal offices and local community involved. We need their informed feedback to succeed in our mission.”
LM’s strategy involves mitigating risks not only from uranium, but also other contaminants such as nitrate, with a focus on establishing a compliance strategy in alignment with groundwater regulations. The Monument Valley site is regulated under Title I of the Uranium Mill Tailings Radiation Control Act (UMTRCA). Surface water and groundwater protection at UMTRCA Title I sites encompasses two strategies: to contain the spread of contaminants to groundwater, surface water, and surrounding lands and to mitigate the threat to public health and the environment from groundwater contaminants.
With the GCAP being developed for Monument Valley, LM will identify a strategy that will be implemented, monitored, and adapted as needed over time to ensure protectiveness. The strategy may consist of one or more proven technologies. The GCAP will be required to meet the standards of the U.S. Environmental Protection Agency and U.S. Nuclear Regulatory Commission.
The Ten-Year Plan to Address Impacts of Uranium Contamination on the Navajo Nation (covering 2020–2029) outlines ongoing and future milestones for the site, including continuing to monitor groundwater, maintaining site infrastructure, and updating conceptual site models based on new data.
The strategy involves evaluating pilot studies and potentially adjusting the GCAP as needed based on the effectiveness of the current remedies, according to the 2022–2023 Ten-Year Plan update.