CHAPTER 2 MODERN IN SITU URANIUM RECOVERY ASSURES NO ADVERSE IMPACT ON ADJACENT AQUIFER USES OR SURROUNDING USDWS
| Jurisdiction | United States |
(Apr 2006)
MODERN IN SITU URANIUM RECOVERY ASSURES NO ADVERSE IMPACT ON ADJACENT AQUIFER USES OR SURROUNDING USDWS
Vice President
Uranium Resources, Inc.
Lewisville, Texas
MARK S. PELIZZA
Mr. Pelizza career in the uranium industry has spanned 28 years; 26 with Uranium Resources, Inc. where he currently serves as Vice President of Health, Safety and Environmental Affairs. He has been involved with some 20 uranium projects. During this tenure, his responsibilities have included: procurement of federal and state environmental permits and licenses, supervision of radiological and non-radiological occupational health, safety and environmental programs, restoration/reclamation/closure, due-diligence and audit, regulatory and community liaison. He has been tendered and qualified as an expert witness in a number of vigorously contested public hearings before state and federal administrative agencies. Mr. Pelizza has actively represented the company and industry trade associations in rulemaking and legislation.
Mr. Pelizza holds a BS degree from Fort Lewis College, a MS from Colorado Sc. of Mines and is a registered Professional Geoscientist in Texas. Professional Affiliations include the New Mexico Mining Association, the Texas Mining and Reclamation Association and the Uranium Producers of America.
1.0 Summary
Water from an aquifer containing uranium ore is not potable and can be exempted1 as an underground source of drinking water (USDW). The presence of uranium and its decay products of radium and radon, cause that portion of the aquifer in which the uranium exists to exceed the maximum contaminant levels ("MCLs") for such radionuclides allowable in public drinking water supplies as set forth in the United States Environmental Protection Agency's (EPA's) National Primary Drinking Water Regulations ("NPDWR") for public water systems.
The modern method of uranium recovery in the U.S.2 leaves the original rock in-place (in situ). This technology has various names, such as solution mining, in situ leach, in situ mining and in situ recovery. For ease of reference, this type of mining is hereinafter referred to as ISR. Instead of manually excavating the rock from underground as in conventional mining and milling the ore on the surface, water wells are used, very much like those for a home. Oxygen is added to the native ground water from the orebody and that water is continuously recirculated until most of the uranium is recovered. The technology used to take the uranium out of the water is the same as that used in home water softeners. Uranium ISR is not new and has been safely used for more than thirty years, with operations in Nebraska, Texas and Wyoming. Waste from ISR uranium recovery is only a tiny fraction of that from a conventional mine, so tailings piles are not needed at the site and the required surface area for ISR facilities is far smaller than that for a conventional mining operation. ISR uranium recovery is highly regulated and monitor wells surrounding the mine site are required, ensuring protection of the surrounding aquifer. Additionally, restoration of the affected portion of the aquifer consistent with baseline conditions or federal or state concentration limits is required.
Approximately 30 commercial ISR operations and numerous pilot projects have been licensed and operated in the United States since the early 1970's. In all of these, some portion of the aquifer outside the mine zone is available as a USDW where engineered wellfield patterns, balanced wellfield operations and monitor wells surrounding the mine area have ensured that water quality outside the mine zone is not impacted.
Once the uranium has been recovered, the affected ground water used in ISR is treated and the quality is restored consistent with pre-mining baseline conditions, or quality of use, as appropriate to ensure that the water quality outside the mine zone will be protected after restoration is completed.
[Page 2-2]
2.0 The Aquifer Containing Uranium Ore is Not Potable Before, During or After ISR Operations
The aquifer at an uranium ISR site cannot now nor in the future provide potable drinking water for the area because it is highly mineralized with naturally-occurring uranium and uranium decay products ("progeny") including radium-226 (226 Ra) and radon-222 (222 Rn), exceeding U.S. EPA drinking water MCLs. Water quality in the aquifer within the adjacent area of review (AOR) surrounding the ISR uranium recovery site will not be affected by the UIC operations because regulations require that injected solutions be limited to the mineralized area. Further, the mineralized interval must be monitored to verify that solutions are contained within it. Monitoring is required in the mineralized sand and, if present, in overlying and underlying sands, containing USDW's until the groundwater restoration process has been completed to the satisfaction of regulatory agencies. As a result, no present or future user of water outside the exempted area within and beyond the AOR will be impacted by a regulated ISR project.
Shown in the Table below, pre-mining water quality information from baseline wells at the Church Rock ISR site in New Mexico provides an illustration which confirms the water exceeds EPA NPDWR MCLs in the uranium ore zones.
| Parameter | Average | EPA MCL |
| Uranium (ppb) | 1,800 | 30 |
| 226 Ra (pCi/1) | 10.225 | 5.0 |
This information demonstrates that the water in this sites ore zone is not now and will not in the future be a USDW because of naturally occurring concentrations of uranium and uranium progeny.
Water found in aquifers with uranium ore contains dissolved radon concentrations in the thousands and even hundreds of thousands of pCi/l concentrations. Given the widely accepted potential hazards of 222 Rn exposure described by EPA, it is reasonable to consider the 300 pCi/l 222 Rn MCL along with uranium and radium MCLs as additional factor that limits groundwater for suitability as a source of drinking water.
Leach solution is not significantly different than native groundwater within the orebody. The radionuclides that limit the pre-ISR use of water (226 Ra, 222 Rn and U3O8) in uranium bearing aquifers are also the primary parameters that limit water use during mining and after restoration. The recovery process does not introduce new chemical species to the groundwater system but does elevate certain species that are native to the host aquifer.
3.0 ISR Technology
In situ uranium recovery involves the circulation of naturally occurring and benign groundwater, fortified with oxygen, through a uranium ore body. This natural water plus oxygen is pumped into injection wells, through the uranium ore body, where the uranium in the host sandstone is oxidized and solubilized, continuing through the sandstone to the extraction wells,
[Page 2-3]
where the uranium-bearing groundwater is pumped to the surface. Next the water proceeds to ion exchange for uranium removal and then is pumped back to the wellfield for re-fortification with oxygen, into the injection wells and again re-circulated through the ore body. This re-circulation of the same groundwater continues over and over, until the uranium in the sandstone is depleted. The native groundwater to which gaseous oxygen and gaseous carbon dioxide and/or sodium bicarbonate have been added is called lixiviant.
Loaded ion exchange resin is then processed into yellowcake. Yellowcake is dried and then stored in drums for shipment to a purchaser at a UF6 conversion, or other nuclear fuel cycle facility.
3.1 Lixiviant Injection/Extraction
Uranium, present in the host ore in a reduced insoluble form, is oxidized by the lixiviant solution injected into the ore zone. Once uranium is oxidized, it complexes with bicarbonate anions in the groundwater and becomes mobile. Uranium recovery proceeds with the continuous recirculation of fortified groundwater leaching solution through the uranium ore from the injection to the production wells. Uranium in the ore reacts with the lixiviant to form a soluble uranyl dicarbonate complex as follows:
2UO2 + O2 ? 2UO3
UO3 + 2NaHCO3 ? NA2UO2(CO3)2 + H2O
The lixiviant, which is comprised of native groundwater fortified with sodium bicarbonate and/or gaseous carbon dioxide and oxygen, is injected into injection wells. After passing through the ore zone, the uranium rich lixiviant is pumped from production wells to the processing facility where the uranium is extracted by ion exchange onto resin. The resulting uranium depleted (barren) water is then refortified with an oxidant such as O2 and reinjected into the wellfield to repeat the leaching cycle. The lixiviant typically consists of the parameter concentrations below.
| Calcium (mg/l) | 100 - 350 |
| Magnesium (mg/l) | 10 - 50 |
| Sodium(mg/l) | 500 - 1600 |
| Potassium (mg/l) | 25 - 250 |
| Carbonate (mg/l) | 0 - 500 |
| Bicarbonate (mg/l) | 800 - 1500 |
| Sulfate (mg/l) | 100 - 1200 |
| Chloride (mg/l) | 250 - 1800 |
| Silica (mg/l) | 25 - 50 |
| Total Dissolved Solids (mg/l) | 1500 - 5500 |
| Uranium (mg/l) | 50 - 250 |
| 226-Radium (pCi/l) | 1000 |
| Conductivity (µS/cm) | 2500 - 7500 µS/cm |
| pH | 7 - 9 |
[Page 2-4]
Injection well and production well flow rates are monitored to assess operational conditions and mineral royalties. The flow rate of each production and injection well is determined by monitoring individual flow meters in each wellfield header. The surface injection pressures does not exceed the maximum surface pressures posted in each wellfield header.
3.2 Ion Exchange (IX)
The uranium rich leaching solution containing the uranyl dicarbonate complex is received at the processing plant through a network of wellfield piping and pumped through the ion exchange columns. Uranium is exchanged on the reacting sites of the resin for chloride as follows where R is a reacting...
To continue reading
Request your trial