This fact sheet provides information about the Tuba City 

site. This site is managed by the U.S. Department of 

Energy Office of Legacy Management under Title I of the 

Uranium Mill Tailings Radiation Control Act of 1978.

Site Information and History Info-square Book-open

The Tuba City, Arizona, Disposal Site is within the Navajo 

Nation and close to the Hopi Reservation, approximately 

5 miles east of Tuba City and 85 miles northeast of Flagstaff, 

Arizona. The Rare Metals Corporation and its successor, 

El Paso Natural Gas Company, operated a uranium mill at the 

site between 1956 and 1966. During its 10 years of operations, 

the Tuba City mill processed about 800,000 tons of uranium 

ore. The milling operations created low-level radioactive mill 

tailings, a predominantly sandy material. The tailings were 

conveyed in a slurry from the mill to evaporation ponds at 

the site. These ponds covered an area of 33.5 acres, and 

windblown tailings affected an additional 250 acres northeast 

of the mill site. The U.S. Department of Energy (DOE) began 

surface remedial action at the Tuba City site in 1988. All 

uranium mill tailings from the onsite piles, debris from 

demolished mill buildings, and windblown tailings were 

moved and stabilized in an engineered disposal cell onsite. 

DOE completed site cleanup in 1990. 

Regulatory Setting LEAF

Congress passed the Uranium Mill Tailings Radiation 

Control Act (UMTRCA) in 1978 (Public Law 95-604), 

and DOE remediated 22 inactive uranium-ore processing 

sites under the Uranium Mill Tailings Remedial Action 

Project in accordance with standards promulgated by the 

U.S. Environmental Protection Agency in Title 40 Code of 

Federal Regulations (CFR), Part 192. Subpart B of 40 CFR 192 

regulated cleanup of contaminated groundwater at the 

processing sites. The radioactive materials were covered in 

disposal cells for control of radon emissions in compliance 

Tuba City, Arizona, Disposal Site

An UMTRCA Title I site

Fact Sheet

with the 40 CFR 192 regulatory standard. The U.S. Nuclear 

Regulatory Commission general license for UMTRCA Title I 

sites is established in 10 CFR 40.27. The Tuba City disposal 

cell was included under the general license in 1996. 

Disposal Site 

The disposal site is approximately 6,000 feet northwest 

of and 300 to 400 feet in elevation above Moenkopi Wash, 

an intermittent stream that drains to the southwest into the 

Little Colorado River. The disposal site lies at an elevation 

of approximately 5,100 feet above sea level on the middle 

of three alluvial terraces associated with ancestral flows in 

Moenkopi Wash. Thin surficial deposits of unconsolidated 

dune sand and alluvial gravels overlie the Navajo aquifer, 

which is the main aquifer near the Tuba City site and is 

regionally vast within sedimentary deposits comprising the 

Navajo Sandstone Formation. The saturated thickness of the 

aquifer near the disposal cell is about 500 feet, although 

within 2,000 feet south of the disposal cell the aquifer thins 

rapidly because of topography and regional groundwater 

discharge at Moenkopi Wash. Depth to groundwater ranges 

from about 60 to 75 feet below land surface. 

Land near the site is used for grazing; adjacent land is 

used for dry and irrigated farming and residential purposes. 

There is no known domestic, industrial, or agricultural use 

of groundwater from the contaminated region of the aquifer. 

Nearby residences receive water from the Navajo Tribal Utility 

Authority; this water comes from a well completed in the 

bedrock aquifer approximately 1.5 miles northwest 

(hydraulically upgradient) of the site. 

Surface water associated with the Tuba City site is located 

approximately 6,000 feet south of the site, where seeps 

are present along cliff bands that border Moenkopi Wash. 

Water from Moenkopi Wash is used for stock watering and 

agricultural diversions by the Navajo and Hopi residents near 
the site. Early site characterization efforts and ongoing 

annual monitoring have found no contamination in the 

seeps in this area. 

Historical milling operations contaminated groundwater 

in the Navajo aquifer. The primary source of contamination 

is water that drained from the unlined evaporation ponds 

and infiltrated into the subsurface. Mill-related contamination 

in the uppermost part of the aquifer has been detected 

2,500 feet south of the original mill tailings impoundment 

location. Groundwater contaminants with concentrations that 

exceed their standards in 40 CFR 192 are molybdenum, 

nitrate, selenium, and uranium. High levels of sulfate are also 

present in the groundwater. Although sulfate is not regulated 

in 40 CFR 192, its concentration in groundwater is high 

enough to cause a potential health risk, and a restoration 

goal was established for comparison to monitoring results. 

Compliance Strategy user-hard-hat

The compliance strategy for contaminated groundwater 

underlying the site is active remediation. The objective of this 

strategy is to remove nitrate and uranium (the primary site 

contaminants) and other site-related contaminants from the 

aquifer to meet 40 CFR 192 standards and other water quality 

restoration goals that are documented in the Groundwater 

Compliance Action Plan (GCAP).

The active remediation system consists of groundwater 

extraction wells located within the contaminated area of the 

aquifer. Extracted water is conveyed to an onsite treatment 

plant where it is pretreated through a water softener, then 

distilled. A double-lined solar evaporation pond receives the 

concentrated liquid waste from distillation and regeneration 

waste from the softener. Treated (distilled) water is returned to 

the aquifer through an infiltration trench located upgradient of 

the contaminant plume. 

The treatment plant is currently in a “safe standby” condition. 

Active remediation continues on an interim basis, through 

conveyance of extracted groundwater directly to the solar 

evaporation pond. In this process, clean water evaporates to 

the atmosphere and contaminants are safely accumulated in 

the pond in dissolved form.

A network of 104 groundwater monitoring wells (surrounding 

the extraction wells) is used to track water quality and water 

level trends. Monitoring well sampling and analyses are 

performed twice annually. Extraction well sampling and 

analyses are performed monthly.

Direct evaporation, as well as other treatment approaches, 

are being studied while operations continue under interim 

treatment status. Studies will lead to a revision of the GCAP, 

with protection of human health and the environment being 

imperative in the development of the future groundwater 

compliance strategy. 

Disposal Cell Design drafting-compass

The five-sided disposal cell occupies an area of 50 acres on 

the 145-acre site. The cell rises 44 feet above the surrounding 

land. An interceptor ditch was constructed on the upslope 

side of the site. A woven wire fence with locked gates 

surrounds the site, and the site perimeter is marked with 

warning signs and permanent monuments. 

The cover of the disposal cell is a multicomponent system 

composed of:

1. a low-permeability radon barrier (first layer placed 

over compacted tailings) consisting of clayey soil,

2. a granular bedding material placed as a capillary 

break, and

3. rock (riprap) erosion protection layers. 

North-South Cross Section of the Tuba City Disposal Cell
IN CASE OF AN EMERGENCY AT THE SITE, 

CONTACT 911.

Site-specific documents related to the Tuba City, 

Arizona, Disposal Site are available on the 

LM website at www.energy.gov/lm/tuba-city-arizonadisposal-site

For more information about LM activities at the 

Tuba City, Arizona, Disposal Site, contact: 

U.S. Department of Energy 

Office of Legacy Management

2597 Legacy Way

Grand Junction, CO 81503

Email:

public.affairs@lm.doe.gov

DOE Office of Legacy Management

(970) 248-6070 (monitored continuously)

(877) 695-5322 (toll-free)

All groundwater and surface water quality data for 

the site are publicly available on LM’s Geospatial 

Environmental Mapping System (GEMS) website at 

https://gems.lm.doe.gov/#site=TUB. New data are 

posted to the GEMS website after each semi-annual 

sampling event.

 www.energy.gov/lm

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 www.linkedin.com/company/legacy-management

The cell location and design were selected to minimize 

the potential for erosion from wind and storm water runoff. 

Surrounding disturbed areas were regraded and reseeded 

with native vegetation.

Legacy Management Activities Digging

The DOE Office of Legacy Management (LM) is responsible for 

ensuring that the selected groundwater compliance strategy 

at the Tuba City disposal site continues to be protective of 

human health and the environment. 

LM manages the disposal site according to a site-specific 

Long-Term Surveillance Plan to ensure that the disposal cell 

systems continue to prevent release of contaminants to the 

environment. Under provisions of this plan, LM conducts 

annual inspections of the site to evaluate the condition of 

surface features, performs site maintenance as necessary, 

and monitors groundwater to verify the continued integrity 

of the disposal cell. 

In accordance with 40 CFR 192.02(a), the disposal cell is 

designed to be effective for 1,000 years, to the extent 

reasonably achievable, and, in any case, for at least 

200 years. However, the general license has no expiration 

date, and LM’s responsibility for the safety and integrity of 

the Tuba City disposal cell will last indefinitely. 

05/2020

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