What Is Uranium and Where Does It Come From?

Uranium is a naturally occurring radioactive element found in rocks, soil, and water throughout the world. It is the heaviest naturally occurring element and is present in various minerals including uraninite, carnotite, and autunite. Uranium dissolves into groundwater as it moves through uranium-bearing geological formations.

Natural uranium concentrations in groundwater are highly variable, ranging from less than 0.001 mg/L to over 1 mg/L depending on local geology and water chemistry. Elevated uranium is found in granitic terrains, sedimentary formations (particularly sandstone aquifers), and areas with phosphate-rich deposits. In the United States, uranium in groundwater is most common in the western states, the Great Plains, and portions of New England.

Uranium solubility is strongly influenced by oxidation-reduction conditions and pH. Under oxidizing conditions, uranium exists as the highly soluble uranyl ion (UO2 2+), which forms mobile complexes with carbonate, phosphate, and other ligands. Under reducing conditions, uranium is immobilized as insoluble uranous minerals.

Anthropogenic sources of uranium in water include uranium mining and milling operations, phosphate fertilizer production (phosphate rock often contains elevated uranium), nuclear fuel processing, and the application of phosphate fertilizers to agricultural land. Legacy uranium mining sites, particularly on Navajo Nation lands and in other western U.S. locations, continue to affect local water supplies.

Health Effects of Uranium in Water

Uranium in drinking water poses both chemical and radiological health risks, though the chemical toxicity is the primary concern at concentrations found in drinking water. The kidney is the primary target organ for uranium's chemical toxicity.

Chronic ingestion of uranium above the EPA MCL can damage the proximal tubules of the kidney, impacting kidney function. Animal studies have demonstrated nephrotoxicity at uranium concentrations above 0.1 mg/L in drinking water. Some human epidemiological studies in populations exposed to elevated uranium in well water have reported associations with biomarkers of kidney damage.

The radiological risk from uranium at drinking water concentrations is relatively low compared to the chemical risk. However, uranium decay products, particularly radium-226 and radium-228, are more radiotoxic per unit mass and are regulated separately under the EPA Radionuclides Rule.

Radon-222, a gaseous decay product of radium-226 in the uranium decay chain, is a separate concern in groundwater. Radon in water releases into indoor air during water use and contributes to inhalation exposure.

Regulatory Limits for Uranium in Drinking Water

The EPA MCL of 0.030 mg/L (30 micrograms per liter) was established in 2000 under the Radionuclides Rule, based on chemical toxicity to the kidney with a margin of safety. The MCLG (health-based goal) is zero.

How to Test for Uranium in Water

Uranium is measured by laboratory analysis using EPA Method 200.8 (ICP-MS) for mass concentration (mg/L) or radiochemical methods for activity concentration (pCi/L). ICP-MS is the most common method for compliance monitoring against the 0.030 mg/L MCL.

Samples should be collected in acid-washed polyethylene containers and preserved with nitric acid. A comprehensive radiological analysis should also include radium-226, radium-228, and gross alpha measurements if uranium is detected at elevated levels, as these co-occurring radionuclides may also exceed their respective standards.

Treatment Methods for Uranium Removal

Strong Base Anion Exchange

Strong base anion (SBA) exchange is the most effective and widely used technology for uranium removal from drinking water. Uranium in the form of uranyl carbonate complexes (which carry a negative charge at typical groundwater pH) is preferentially removed by SBA resins. Ion exchange systems for uranium typically achieve effluent concentrations below 0.001 mg/L. Spent resin accumulates uranium and may be classified as radioactive waste, requiring specialized disposal.

Reverse Osmosis

Reverse osmosis systems achieve uranium rejection rates above 95%, producing permeate well below the MCL. RO simultaneously removes other dissolved contaminants including radium, TDS, and other inorganic constituents. The RO concentrate contains elevated uranium and requires proper disposal or treatment.

Coagulation and Filtration

Conventional coagulation with ferric chloride or aluminum sulfate, followed by sedimentation and filtration, can achieve 80-95% uranium removal. This process is used primarily in municipal water treatment plants and requires optimization of coagulant dose and pH.

Activated Alumina

Activated alumina adsorption can remove uranium from water, though it is less commonly used than ion exchange. Performance depends on pH, with optimal removal occurring at pH 5-6. The media requires periodic regeneration or replacement.

Lime Softening

Lime softening at elevated pH (above 10.5) can co-precipitate uranium with calcium carbonate and magnesium hydroxide, achieving removals of 85-99%. This process generates uranium-containing sludge that requires characterization and appropriate disposal.

Frequently Asked Questions

How does uranium get into drinking water?

Uranium enters drinking water primarily through natural geological processes. It dissolves from uranium-bearing minerals in rock formations, including granite, sandstone, and phosphate deposits, as groundwater passes through them. Uranium is naturally present in aquifers across many regions. Mining and milling operations, phosphate fertilizer production, and nuclear fuel cycle activities are anthropogenic sources.

Is uranium in water radioactive?

Yes, naturally occurring uranium is radioactive, consisting primarily of uranium-238 (99.3%) and uranium-235 (0.7%). However, at concentrations found in drinking water, the primary health concern is chemical toxicity to the kidneys rather than radiation exposure. The EPA MCL of 0.030 mg/L (30 ppb) was established based on chemical toxicity, not radiological risk.

What is the best treatment for uranium in well water?

Strong base anion exchange is the most widely used and effective technology for uranium removal from drinking water, achieving effluent concentrations well below the EPA MCL. Reverse osmosis is also highly effective, with rejection rates above 95%. The choice between technologies depends on water chemistry, flow rate, and operational considerations.

Need to Remove Uranium from Your Water?

ForeverPure provides commercial and municipal uranium treatment systems, including strong base anion exchange, reverse osmosis, and coagulation-filtration systems. Our engineering team designs uranium removal solutions that meet EPA MCLs and addresses waste management requirements for uranium-containing residuals.

Contact ForeverPure for a customized uranium removal solution.