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Protecting the Westwater Canyon Aquifer: Why Uranium ISL Mining Threatens Navajo Drinking Water

By Chris Shuey

Community opposition to proposed uranium in situ leach (ISL) mining in Church Rock and Crownpoint chapters is based in large part on concerns that the mining threatens the high-quality groundwater resources of the Eastern Navajo Agency. The mines would use a chemical solution to extract uranium from the Westwater Canyon Aquifer, a vast underground reservoir that is the principal source of drinking water for at least nine Navajo communities, including the town of Crownpoint. Residents say that people come from more than 50 miles away to haul Crownpoint's "pure, sweet-tasting" water, and that at least 15,000 people in the region depend on wells that tap the Westwater for their only source of water for human and livestock uses.

The potential impacts of ISL mining on groundwater quality have been debated scientifically in the communities' ongoing legal challenge of Hydro Resources, Inc.'s (HRI) ISL mining license before the U.S. Nuclear Regulatory Commission (NRC). The Intervenors, Eastern Navajo Diné Against Uranium Mining-Concerned Citizens of T'iists'óóz Nídeeshgizh (ENDAUM-CCT) and Southwest Research and Information Center (SRIC), argue that the risk of contamination is too great to justify ISL mining in a currently used underground source of drinking water. In this article, we review the technical bases of these groundwater concerns and discuss why successful post-mining groundwater restoration is unlikely.

Background: The ISL Mining Method

HRI proposed the Crownpoint Uranium Project (CUP) in a license application filed with the NRC in 1988. NRC issued a Final Environmental Impact Statement (FEIS) in February 1997, and in January 1998, granted a license to HRI to construct and operate ISL mines at three sites: Church Rock (which is now defined as two separate mine units, Section 8 and Section 17), Unit 1 located 2.5 miles west of Crownpoint, and Crownpoint (Figure 1). Injection and production wellfields would be constructed at each of the four mines. Satellite processing plants would be constructed at Church Rock Section 8 and Unit 1. Uranium in resin-slurry form would be transported by tank trucks to a central processing plant in Crownpoint for final processing and drying into a metallic oxide powder (U3O8), called "yellowcake."

In the ISL mining process (Figure 2), hundreds of water wells are drilled into the uranium-bearing rock formation; no vertical shafts are developed as in conventional underground mining. A solution of water containing dissolved oxygen and sodium bicarbonate - called lixiviant - is pumped into the uranium-ore zones of the formation. The oxygen oxidizes the rock as the solution flows through it; the sodium bicarbonate acts as a rinsing agent that strips the uranium molecules from the sand grains of the rock. The resulting uranium-laden solution - called pregnant lixiviant - is pumped to the surface for separation and concentration of the uranium into its oxide form.

The key fact is that, for ISL mining to work, the process must deliberately contaminate the aquifer with enough uranium to make mining financially feasible. Under HRI's plan, uranium concentrations in the mining zones would be increased 20,000 to 100,000 times above the average background level of uranium in the Crownpoint municipal water wells, and from 7,140 to 35,700 times the average level of uranium in the non-mineralized portions of the aquifer at the Church Rock site. In addition, injection of lixiviant also increases a wide range of heavy metals and radionuclides that are hazardous to human health. As we discuss below, ENDAUM's and SRIC's experts are convinced that HRI will not be able to prevent this "toxic soup" from migrating into the high-quality groundwater of the Westwater Canyon Aquifer.

Hydrology of the Westwater Canyon Aquifer

Sandstones, siltstones, mudstones and conglomerates derived from ancient, buried stream channels make up the Westwater Canyon Aquifer. In the parlance of hydrogeologists, the Westwater formation is highly heterogeneous and anisotropic. That's a fancy way of saying that the type and composition of the rocks, and the direction and speed of water moving through the rocks, vary considerably throughout its total thickness of 250 feet to 300 feet. The channels themselves crisscross laterally and are stacked on top of each other. The uranium ore bodies are inside long, narrow and thin layers.

The Intervenors' experts say that HRI wrongly modeled the Westwater as homogeneous - as one big pile of sand with no lateral boundaries, through which water moves slower than a snail's pace. Those groundwater experts postulated that lixiviant control will be jeopardized because groundwater moves faster in the narrow and thin channels than in the surrounding rock, thus speeding up migration of contaminants outside of the mine zones into fresh groundwater. They said results of HRI's own aquifer pump tests showed varying hydrologic conditions consistent with aquifer heterogeneity. They also noted that HRI's plan to space perimeter monitor wells at 400-foot intervals could allow contaminants to escape undetected because the channels that contain the uranium vary from 30 feet to about 150 feet in width. Should pregnant lixiviant escape the mining area, the strong oxidizing effects would overwhelm the natural buffering capacity of the rocks, contrary to HRI's insistence that mining fluids will not escape the mine site.

The company's technicians assert that modeling the Westwater as a homogeneous aquifer is standard practice in the ISL industry. Besides, they said, they would maintain hydrologic balance in the wellfields sufficient to prevent lixiviant migration. The NRC staff concurred with HRI's analysis. And in August 1999, an NRC administrative judge dismissed the Intervenors' groundwater concerns about the Church Rock Section 8 site. He found that the Intervenors' "channel theory" was unsupported, that the Westwater Aquifer is homogeneous, and that HRI had adequately demonstrated that it would not contaminate an underground source of drinking water.

The Intervenors' believe the judge ignored this evidence and intend to appeal his decision once the entire license adjudication is completed. In the meantime, the issue of lixiviant containment remains a concern at the other three mining sites. One of Crownpoint's municipal wells is located less than a half mile - and hydrologically downgradient - from the proposed Crownpoint mine site wellfields; the other is located 1.5 miles from the mining site. Thus, the town's pristine water is directly in the line of escaping lixiviant. One of the Intervenors' experts testified that such "excursions" are commonplace in ISL operations. He found agency reports on more than 40 excursions at three ISL mines in Wyoming and 12 ISL mines in Texas during the period 1989 through 1998, with about a third of those still ongoing at the end of 1998.

Water Quality of the Westwater Canyon Aquifer

The overall quality of ground water throughout the Westwater Canyon Aquifer is good to excellent. The amount of dissolved solids in the groundwater is very low, and the uranium levels in the Crownpoint municipal wells are miniscule. The Crownpoint water is so good that the Navajo Tribal Utility Authority does not filter the water to make it safe. It simply adds chlorine to kill harmful bacteria in the water distribution system and fluoride to promote dental health.

If the Westwater is so clean, why does HRI repeatedly assert that the aquifer is already contaminated and unfit for human use? The answer lies in the geochemical conditions in the Westwater and how the aquifer is tapped for municipal water supplies. Under natural conditions, the aquifer is low in oxygen, which allows the uranium molecules to stay attached to the sand grains of the rocks. Only trace amounts of uranium enter the groundwater. Municipal wells are screened throughout the entire thickness of the aquifer, allowing water to enter the wells from each sublayer of the formation. High levels of uranium only occur in the groundwater immediately adjacent uranium ore deposits and are diluted by the tremendous volumes of clean water produced in the municipal wells.

What, then, is Baseline Water Quality, and Can Restoration to Baseline be Achieved?

HRI is required by license condition to determine baseline water quality for each mine before mining begins. That baseline is critical because it is used to establish post-mining restoration standards. Even though HRI conducted pre-mining water quality testing at all four sites in support of its license application, and NRC published the results of that testing in the FEIS, baseline water quality and final restoration standards have not been set. How, then, can anyone tell if HRI will be successful restoring the groundwater after mining ends?

Restoration success can be predicted from previous experience in the ISL industry in New Mexico, Wyoming and Texas. The Intervenors' experts concluded, based on an extensive review of restoration performance of both pilot-scale and commercial mines in the three states, that the likelihood is minimal that restoration to true baseline water quality levels will be possible at the HRI ISL mines. The long-term consequences of restoration failure at ISL operations in Wyoming and Texas are serious, but the native groundwater quality is poor to fair. There is no such margin for error in Church Rock and Crownpoint where the natural water quality is good to excellent; failed restoration is simply not an option.

The Mobil Section 9 Experience

The ISL restoration experience that is most relevant for gauging HRI's probability of success was restoration undertaken by Mobil Oil Corporation at its Section 9 ISL Pilot Project near Crownpoint in the early-1980s. An examination of restoration results for the Section 9 project revealed that the Mobil restoration was largely unsuccessful. The Section 9 pilot plant was operated for only 10 months in 1979 and 1980, and involved only 13 production wells. Yet, during a restoration phase that lasted for 7 years, restoration to baseline water quality values in the Westwater Aquifer was not achieved for 72 percent of 25 tested chemical parameters. For several important health-based parameters, such as radium-226, arsenic and uranium, the "baseline" restoration goals that Mobil could not satisfy were statistically inflated over true baseline with the blessings of New Mexico regulators.

The importance of Mobil's unsuccessful restoration experience cannot be overstated. It occurred at a pilot-scale operation that was a small fraction of the magnitude of HRI's project. Restoration was attempted over a 7-year period; HRI anticipates completing restoration for the much larger Church Rock Section 8 mine in less than 5 years. Mobil flushed the leach zone nearly twice as many times as NRC will require of HRI, and four times more than HRI asserts is necessary. Most important, Mobil could not to return water quality in the aquifer even to the regulatory level that was worse than its original condition.

The Wyoming and Texas Experiences

Neither has groundwater restoration at commercial-scale ISL mines in Wyoming and Texas always been successful. In fact, restoration to original baseline levels generally has not been achieved without relaxing restoration standards in both states. Additionally, restoration has always taken longer than originally anticipated and is still ongoing at several commercial ISL wellfields that began operating in the 1980s and '90s.

In Wyoming, restoration to baseline levels had not been achieved at seven of nine wellfields at three ISL mines through 1998. Restoration was certified at the Bison Basin Project only after the state of Wyoming was forced to relax restoration standards because bond money left by the company that abandoned the site was not sufficient to cover the costs of restoration to pre-mining baseline.

In Texas, the Water Commission certified completion of restoration at two ISL mines operated by Uranium Resources, Inc., HRI's parent company, only after relaxing key restoration standards in 1987. In all of the cases, the actual uranium restoration levels achieved by URI satisfied the relaxed standards, but exceeded the original standards established by pre-mining water quality assessments. Texas regulators based their approval of the higher uranium restoration standards on the fact that most ISL operators were failing to achieve compliance with the more stringent baseline values.

Uranium Nephrotoxicity: Why NRC's Restoration Standard is Unsafe

The only restoration standard established by the NRC for the Crownpoint Project is for uranium. The standard - 0.44 milligrams per liter (mg/L) - would be implemented if baseline uranium levels were, on average, less than 0.44 mg/L. In that case, allowable residual uranium levels in the aquifer after mining could be substantially higher than baseline. If, on the other hand, baseline uranium levels were greater than 0.44 mg/L, then the higher levels would become the restoration standard.

SRIC's research, and testimony by Crownpoint physician John Fogarty, supports the view that the NRC uranium limit is unsafe for a drinking water aquifer. As shown in Table 2, the NRC standard is up to 40 times greater than the lowest level of subclinical effect of chronic uranium ingestion on the human kidney observed in three recent population-based epidemiological studies. The standard is 14 times greater than the federal drinking water standard (0.03 mg/L) and is up to 220 times higher than the most restrictive international water quality guideline. Most important, the standard is 62 times greater than non-ore zone baseline water quality at the Church Rock site and nearly 200 times greater than the average uranium concentration in the Crownpoint municipal wells.

The New Navajo ISL Policy: Water Is Our Most Valuable Resource

When Navajo Nation President Kelsey Begaye and Vice President Dr. Taylor McKenzie issued a new policy opposing ISL mining in Navajo communities, they wrote: "The public health ramifications of widespread contamination [from in-situ uranium mining] are enormous given the potential renal toxicity of uranium. . . .The water resources of the Navajo Nation are among its most valuable resources and must be protected. Therefore, the Executive Branch is opposed to any in-situ leach uranium mining operations that would involve pumping water from or injecting lixiviant into potable or potentially potable groundwater or surface water sources." (See Voices, Fall 2002, pages 2-3.)

These Navajo leaders get it - once lixiviant is injected into the mining zone, the chemical changes in the native groundwater are substantial and pervasive, and may not be completely or even partially reversible. That is also why so many residents of the Eastern Agency have said for many years that the HRI project "could destroy our precious water supplies."

1 Data and information are excerpted from briefs, written testimonies, and supporting documentation contained in NRC hearing record (NRC Docket No. 40-8968-ML and ASLBP No. 95-706-01-ML) and information from the files of Texas and Wyoming regulatory agencies. Contact the author at sricchris@earthlink.net for specific references.

2 These experts are Michael Wallace, MA, a hydrogeologist who has modeled "salt creep" at the WIPP site near Carlsbad; Spencer Lucas, Ph.D., an authority in the depositional history of the Jurassic sediments of northwestern New Mexico; Richard Abitz, Ph.D., a geochemist who oversees restoration of uranium-contaminated ground water at the government's Fernald uranium plant near Cincinnati; William Staub, a geophysicist who wrote the NRC's only evaluation of uranium ISL mine restoration performance in 1985; and April Lafferty, MS, a geologist and former ISL restoration surety specialist for the state of Wyoming.

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