Groundwater Protection and Restoration During In-Situ Uranium Recovery
What preliminary studies and sampling will be completed in order to determine the baseline conditions of the aquifer?
Azarga crews have been collecting data at its projects since 2007. Aquifer pump tests have been performed to define the hydrological characteristics of the ore zones, obtain information about the direction and velocity of ground water flow, and identify the composition, porosity, permeability, and hydraulic gradients of the ore zones and adjacent geologic strata. This information will assist in designing the optimum well field configuration, or pattern and spacing for injection and recovery wells, as well as determine the appropriate procedures to confine the recovery solution to the ore zones. Also, all water supplies under and surrounding the site will be monitored before and throughout the recovery process to document water quality. At the end of mining, the company is required to return groundwater quality to a level consistent with the original quality prior to mining.
Where is the uranium ore zone located in the aquifer?
In the Centennial Project, as well as the Dewey Burdock Project, the uranium is contained in sandstone formations created millions of years ago. The Centennial host is known as the Fox Hills formation. In Dewey Burdock the uranium is contained in a similar sandstone horizon known as the Inyan Kara Group. In both projects, some water is produced from these horizons. However wells are located at a considerable distance from the uranium ore. The depth varies from 80 – 600 feet below the surfacein Centennial and generally from 200 to 800 feet deep at Dewey Burdock. Depth depends on the thickness of the over-lying strata and the regional dip of the host formations. These aquifers naturally have heavy metals present, the foremost of which is uranium.
Native groundwater from the uranium ore zone is used for all ISR operations. A small portion of the water is extracted and is charged with oxygen and carbon dioxide and is reinjected in adjacent wells. The water will be recirculated over and over through the ore until all the uranium is extracted. Our objective is to minimize consumption of water to the highest extent possible.
The water in ore zone at the mine site has a naturally high mineral content that makes it unsuitable for human use, livestock or agriculture. This water is not suitable now nor will it be useable in the future as a source of water.
The water used in the mining operations, like all ground water, is derived from the pore space in the rock. Where uranium ore bodies occur, the pore space also contains the uranium ore which can be dissolved and brought to the surface for processing.
The water that is used in the mining operations is derived from the pore space in the rock that contains the uranium ore. During in-situ operations, about 99 percent of the native groundwater is continually recirculated and is not consumed. However, a one percent bleed is required by regulation, which will be diverted to a reverse osmosis filtration unit. Assuming an operation flow rate of 2000 gallons per minute, this would result in 20 gallons per minute being diverted to the filtration unit with approximately 14 gallons per minute being recirculated to the well field and 6 gallons per minute being disposed of via deep well injection. The net consumptive use of water is approximately 6 gallons per minute, nearly the same flow as a garden hose. To reiterate, the company’s objective is to minimize consumption of water to the greatest extent possible.
How many wells will there be?
The number of wells is dependent on the final engineering study. However, in the area of the ore, wells will probably be spaced between 75-100 feet apart. In the ISR process, wells need to be closely spaced in order to extract the uranium, due to its tendency to re-precipitate in the subsurface environment over longer distances.
The Chemistry of the Operational Solutions
Does the water used in the recovery process contain harmful chemicals?
No. The recovery solution is a completely non-toxic mixture of water, oxygen and carbon dioxide. While some in-situ operations in foreign countries have commonly used stronger leaching agents, such as sulfuric acid, which is more reactive and leaches out much more of the metals and salts and takes longer to restore, these operations are regulated by a different standard and are irrelevant to the U.S. industry. Azarga neither intends nor plans to use any acidic recovery solution.
Will the recovery solution and injection pressure have any impact on the aquifer rock formations?
No. No U.S. aquifer has ever been damaged by ISR mining and there will not be any lasting effect on the ore zone rock formation with the Centennial Project. Upon completion of ISR operations, the subsurface touched by the recovery solution returns to a state just as it was prior to mining.
Will the recovery solution loaded with heavy metals spread outside of the ore deposit into underlying or overlying aquifers?
No, for several reasons:
Nature of the Strata: Previous studies have revealed that the ore zone is confined above and below by layers of impermeable strata (mudstone/siltstone), through which the solution cannot travel.
Wellfield Design: The proposed ISR operations are designed to isolate the operational portion of the ore zone from any surrounding zones that contain potable water. This necessity to confine the operations to the uranium zone is a primary requirement by the regulatory authorities before a company is allowed to mine. The movement of the recovery solution through the ore zone is controlled by the design and operation of the ISR system, instrumentation and monitors of the wellfield and the monitor wells that surround the wellfield. Once the uranium is dissolved, the loaded recovery solution is pumped to the surface, and this extraction pressure keeps the solution moving through the ore in the closed recovery process.
Bleed Pressure: Furthermore, slightly more water will be withdrawn than is re-injected, known as a bleed, which maintains a “cone of depression” in the mining area. Because water flows from high to low water levels, this gradient results in a flow from the ore zone up into the production well, confining the recovery solution to the mining zone.
Monitoring: As a final safeguard, the ore zone will be surrounded, both laterally and above and below, by monitor wells which are frequently sampled to ensure that all mining fluids are retained within the mining zone. This zone is surrounded by the mandated monitoring wells surrounding the mine zone, and those wells are measured daily by highly-trained staff for water level (indicator of flow direction), as well as chemistry on a weekly basis that tells if indicator elements that are more mobile than uranium can be detected. Any imbalance in a well field can be reversed by increased pumping in the wells that are closest to the monitor perimeter to level out any imbalance.
What happens to the small amounts of recovery solution withdrawn to create a cone of depression?
During operations, the small waste stream known as a ‘bleed’ is directed to a reverse osmosis filtration unit. This waste stream is typically only one to three percent of the production solution. The filtration unit removes the waste that is then disposed of via deep well injection approximately 2,200 to 3,500 feet deep in tightly confined strata. The “clear” permeate is then recirculated to the well field.
Can residents and livestock remain living and drinking well water next to the ISR recovery
Absolutely. The areas surrounding the permit areas will be safe for all activities, just as they are today. The only reason for restricted activity on an actual ISR permit site is that drilling rigs, vehicles, well heads, monitoring equipment and backhoes are treated as industrial operations and restricted to qualified personnel only for safety of the public and livestock.
As required by law, all water supplies surrounding a site that involves ground water chemistry are monitored so the public can be confident that their safety is not compromised. With regular testing, the population can rest assured that their drinking water is not affected.
Will the recovery solution extract elements other than uranium from the ore zone?
We are currently working to determine the baseline water quality and the level of uranium and other elements that are currently present in the strata in the mine area. Depending on the geochemistry of the ore zone, the recovery solution can also dissolve small quantities of other naturally-occurring elements in the underground strata and existing groundwater. Testing of the ore will tell us which metals are present and in what quantity they may be solubilized under oxidizing conditions.
Some of the metals are re-circulated with the injection solution and not removed (or precipitated) until the end of the recovery process at the groundwater restoration phase. Any precipitated metals would be packaged and disposed of at a licensed facility.
How will those elements be disposed of?
Barium chloride and ammonium sulfate can be added to the recovery solution at the on-site processing facility to precipitate out radioactive radium. The precipitated radium and some associated metals will be further concentrated to reduce volume, then packaged, transported by licensed truck or rail, and disposed of at an NRC-approved disposal site.
Some of the metals are re-circulated with the injection solution and not removed (or precipitated) until the end of the recovery process at the groundwater restoration phase. These precipitated metals, such as selenium, also would be packaged and disposed of at a licensed facility. The NRC approved waste facilities are the Cañon City Mill in Cañon City, Colorado owned by Cotter Corporation, the White Mesa Mill in southeast Utah owned by Denison Uranium Corp., the Shootering Canyon Mill in east central Utah owned by Uranium One, the Sweetwater Uranium Mill owned by Kennecott Mining Corp. in Wyoming and a commercial disposal site located in Clive, Utah.
Will Azarga restore the groundwater after the recovery process?
Yes. Regulatory agencies require that groundwater be returned to a quality as close to pre-mining (baseline) conditions as can practically be achieved. After the completion of uranium recovery in a particular mining area, licensees are required to restore the affected groundwater to established standards to assure the protection of public health, safety and the environment. Any assertion that Azarga will request lower standards or exemption from regulation of groundwater quality is completely untrue.
After being treated to remove metals and salts, the purified groundwater is either reinjected into the aquifer or used as irrigation water in a process called land application. The appropriate method to be used at the Azarga projects will be determined after further testing of the aquifer and the ore zone.
Are there proven examples of successful groundwater restoration after in-situ mining?
Yes. The groundwater restoration, or cleanup of an aquifer impacted by in-situ uranium solution mining has been shown to be technically, physically and economically achievable. (Ref. NRC NUREG/CR 6870) Some recent successful ISR mine closures include the O’Hern, Hobson, Zamzow, Pawlik, and Longoria mines in South Texas, all owned by different companies. There are no historical cases in the United States where ISR has made a long-term negative impact on public health or the environment.