Naturally occurring radioactive substances are frequently found in groundwater—including uranium, a heavy metal. It exists in almost all rocks and soils. Everyone ingests or inhales small amounts of natural uranium daily.
Is my private well at risk?
The presence of uranium in groundwater depends on rock and soil types. A 2009 U.S. Geological Survey study of groundwater used by residential wells showed the highest concentrations occur most often in Western basin-fill aquifers and in crystalline-rock aquifers in the Rocky Mountains and the Northeast.
Geochemical conditions can affect the degree to which naturally occurring uranium enters groundwater. Such conditions include dissolved oxygen and carbonate alkalinity, which contribute to higher levels of uranium in California’s Central Valley and the Newark Basin sediments of northern New Jersey, for example. Generally, uranium is more likely to be present in granite or alkaline sandstone and shale bedrock.
Uranium presence also can result from human actions such as uranium mining and milling and use in some phosphate fertilizers.
What is the measurement of uranium?
What are the health risks from uranium?
How can I address unsafe levels of uranium in my water?
For an existing well, ask the water well contractor about retrofitting the well to bypass water intake zones with higher levels of uranium. Another option is water treatment from a qualified water treatment system provider.
Accurate test results from a certified drinking water testing lab are key to getting appropriate water treatment. A gross alpha test—typically around $30—serves as a preliminary screening that determines whether additional testing is advisable. If results show 15 picocuries per liter or greater, a test for uranium is recommended, which can be twice as expensive. Water samples should be taken carefully according to lab instructions.
Water treatment options for uranium
Reverse osmosis (RO)—RO can remove up to 90 percent of uranium and treat a variety of other water quality issues. Typically, RO is a point-of-use (POU) device installed where the water is used (i.e., under the kitchen sink). It also can be used at the point-of-entry (POE) into the house so that all water is treated.
With POU RO units, a minimum three gallons of wastewater is discharged for every gallon of treated water produced. Since low concentrations of soluble minerals such as calcium, magnesium, iron, and manganese can foul an RO unit, some pretreatment device may be needed.
Maintenance involves replacement of filters and membranes. Filters should be handled carefully and disposed of properly due to potentially high uranium concentrations.
Ion exchange—This involves a physical/chemical process in which water passes through a specialized resin, inducing an exchange of ions removing uranium. For low levels of U in well water, softening ion exchange will remove U below the target level. Ion exchange is typically used in POE treatment systems.
Maintenance can involve replacement or regeneration of media and cartridges. Spent media and cartridges must be handled carefully and disposed of properly due to potentially high uranium concentrations.
Distillation—Distillation, involving evaporating water and condensing the vapor, requires significant heat energy and cooling capacity. It is generally used in POU systems. Residue disposal must be done according to applicable regulations. Filters should be handled carefully and disposed of properly due to high uranium concentrations.
There are voluntary performance testing programs for water treatment systems, such as those operated by NSF International and the Water Quality Association—although there may not be systems listed that have been evaluated for effectiveness in dealing with uranium. Your water well system contractor can determine whether a system has been independently performance tested.
Both RO and ion exchange produce a waste stream, either of RO concentrate or ion exchange backwash discharge. Work with local health officials on avoiding adding more concentrated U to local groundwater or surface water.