SANTA ANA PUEBLO, N.M. — The Department of Energy’s Office of Legacy Management is reassessing its reliance on natural attenuation at some uranium legacy sites after monitoring showed the approach is not meeting cleanup targets, a senior official said.
William “Bill” Frazier, a program manager with DOE Legacy Management (LM), said the office is evaluating whether additional engineered remedies are needed.
Natural attenuation, or intrinsic remediation often paired with monitoring, leans heavily on nature’s natural forces to gradually break down contamination over time.
“Natural attenuation has been shown not working for us,” Frazier said during a panel at the CLEAN Energy Association of New Mexico’s Nuclear in New Mexico conference. At some sites, he said, contaminant concentrations and plume boundaries are not decreasing “fast enough or reliably enough” to meet performance objectives.
Frazier cited ongoing work at sites in New Mexico’s Grants Mining District — including Bluewater, Ambrosia Lake and the L-Bar mill near Laguna Pueblo — where performance concerns are prompting closer review. At Bluewater, a water‑collecting depression on the disposal cell has fueled public scrutiny about potential infiltration.
At the Mexican Hat site in Utah, construction‑related segregation of cover materials led to erosion piping that can create preferential pathways for water and potential contaminant migration, raising questions about the stability and integrity of the disposal cell.
The issues are driving increased scrutiny of disposal cell design and as-built documentation as sites transition into long-term stewardship under DOE, he said.
Under DOE’s remedial framework, underperforming natural attenuation can trigger contingency actions such as pump-and-treat, enhanced bioremediation or other active controls. Such measures can increase life-cycle costs and extend cleanup timelines across the uranium mill tailings portfolio.
Frazier said LM is prepared, in limited cases, to accept more complex regulatory arrangements if they accelerate cleanup.
At the Church Rock site, he said LM has agreed in principle to a “sandwich” configuration that would place mine waste atop an existing DOE disposal cell. The design would effectively create a dual-regulated facility subject to Environmental Protection Agency and Nuclear Regulatory Commission oversight, in addition to DOE’s custodial responsibilities.
The Office of Legacy Management does not favor that level of complexity but is willing to proceed “to help the environment and the public,” Frazier said.
Frazier said Legacy Management is also evaluating whether some existing disposal sites could accommodate more cells dedicated to mine waste within their current footprints. Such an approach could alter how those facilities are classified and regulated and could influence future waste-routing decisions across the complex.
Panelists said attention is increasingly shifting beyond mill tailings to mine waste and groundwater impacts across New Mexico.
Ashley Arrossa, a senior environmental engineer with INTERA Inc., which supports the New Mexico Environment Department, cautioned against expanding the use of small, dispersed repositories for abandoned uranium mine waste. Arrossa cited concerns about monitoring and institutional control.
The discussion comes as federal and state agencies face growing pressure to prioritize limited cleanup funding across legacy uranium sites, particularly in the Grants Mining District, where contamination is widespread and technically complex.