The Nambé area is well known for high uranium concentrations in private water wells, one of which was laboratory-tested to be about 60 times the U.S. Environmental Protection Agency’s maximum contamination level (MCL) of 30 parts per billion (ppb). If you read my previous column, I cited recent work that the uranium found in wells east of the Rio Grande was determined by uranium isotope comparison to be naturally occurring and not anthropogenic. But that does not make it any less potentially harmful to human health.
In the Nambé area, about half of all wells tested have uranium concentrations above the safe drinking-water standard. It is worth noting that EPA standards are more lenient than those of other developed countries: 30ppb in the U.S. compared to 20ppb in Canada, Australia and New Zealand, 15ppb recommended by the World Health Organization, and 2ppb in Japan.
So if the uranium in the Nambé area is naturally occurring and not from Los Alamos National Laboratory, then what are the geologic reasons for high uranium levels in aquifer water? The following explanation is based on field and laboratory work done by geoscientists at the New Mexico Bureau of Geology and Mineral Resources, NM Tech, the NM Environment Dept. and LANL, and published in a NM Geological Society Guidebook.
There are actually four potential sources of uranium in Española Basin groundwater: altered volcanic ash beds that were deposited within the Tesuque Formation, the alteration of volcanic and granitic erosional debris within the Tesuque Formation, the weathering of uranium-bearing (non-commercial at this time) granitic and metamorphic rocks in the nearby mining districts, and weathered Precambrian granitic rocks in the Sangre de Cristo Mountains. Exposures of coarse-grained uraniferous sandstones at the Oxide Butte outcrop will activate a Geiger counter.
I would like to be able to say that there is a direct correlation between well depth and uranium concentrations, but that has not been confirmed. Many well owners do not have accurate information about the depth of producing intervals in their wells. If I had to speculate, I would say that shallow wells near streambeds (both ancient and current) pose the biggest risk.
According to the Centers for Disease Control, most uranium dissolved in water is eliminated from the body, but a small amount is absorbed into the bloodstream and carried to organs. The CDC identifies the kidney as the organ at greatest risk from uranium but downplays the risk of acquiring cancer from uranium radioactivity other than increasing the risk of cancer over a lifetime. From the reading I have done, there really are not any studies directly linking uranium in water to health, but ingesting high levels seems like an overall bad idea considering what we do know and that uranium is so easily removed by certain technologies.
My advice is to get your well water tested and make your own decisions. While you are at it, I recommend including arsenic, selenium and fluoride in the test suite as all these constituents may also occur at high levels in the Nambé area.
Stephen Wiman has a background in earth science (Ph.D. in geology) and is the owner of Good Water Company and a member of the City of Santa Fe’s Water Conservation Committee. He may be reached at 505-471-9036 and firstname.lastname@example.org.