Uranium levels in Pigeon Spring, just north of the Grand Canyon, are likely due to a natural source of uranium and not related to the nearby former Pigeon Mine, according to a recent study by the U.S. Geological Survey.
Pigeon Spring had elevated uranium levels in recent samples from 2012-2014 (73-92 micrograms per liter), compared to other perched springs in the same drainage area (2.7–18 micrograms per liter), and was proportionally elevated in samples collected prior to mining operations at the nearby Pigeon Mine.
The Grand Canyon National Park in Arizona is a United Nations World Heritage Site, an international tourist destination, and is a sacred place to many Native Americans. The Colorado River, which runs through the Grand Canyon, is a primary source of drinking and irrigation water for millions of people in the U.S. and Mexico. The region is also believed to host some of the highest-grade uranium ore in the country. Understanding the potential for uranium mining impacts on water resources in the area is important to manage the intersecting interests of the mining industry, water managers and visitors to the area.
“It’s important to use science to understand the potential for mining impacts on water resources,” said Kimberly Beisner, USGS scientist and lead author of the study. “These results are the first step in understanding if uranium mining in the area may have any impact on water resources; in this case we determined those impacts are not likely at Pigeon Spring. These findings will help inform future studies to understand mining impacts in the region.”
USGS scientists conducted a geochemical analysis of water, sediment and rock samples collected from the Snake Gulch area, which includes the former Pigeon Mine. Scientists studied water from nine springs, along with water that had been in contact with uranium mining waste material to better understand the source of elevated uranium at Pigeon Spring. Statistical analyses of trace elements, chemical elements that occur in small amounts, showed Pigeon Spring to be more similar to other nearby springs and distinct from water in contact with uranium mining material. Water in contact with mining material from the Pigeon Mine contained elevated levels of several trace elements in addition to uranium compared to the spring water. Additionally, evidence from available groundwater level measurements in the area indicate that groundwater is probably flowing towards the northwest, whereas Pigeon Spring is due east of Pigeon Mine, making groundwater impacts from the mine on the spring unlikely.
“Unbiased scientific studies such as these provide important information that can be used by decision makers tasked with balancing the demands of national energy independence with the need to protect our natural resources, especially water” said Michael Focazio, coordinator for the USGS Toxic Substances Hydrology and Contaminant Biology Programs that supported the study.
This study was completed to help answer science questions set forth in the 2012 Record of Decision by then U.S. Secretary of Interior Ken Salazar to withdraw over 1 million acres of federal land in the Grand Canyon region from new uranium mining activities for 20 years. USGS studies are being conducted to better understand the potential impacts of uranium mining activities on cultural, biological and water resources in the area.