YELLOWSTONE NATIONAL PARK — In this week’s Caldera Chronicles, the scientists of Yellowstone Volcano Observatory (YVO) discuss the principles of safe drinking water in the Yellowstone National Park (YNP) backcountry.
Caldera Chronicles is a weekly column written by the scientists and collaborators of YVO. This week’s edition was written by Blaine McCleskey, a research chemist with the U.S. Geological Survey (USGS). McCleskey takes up the topic of drinking water supply in the backcountry, and breaks down the three water types in YNP.
Thermal water, the first type mentioned, should not be used as drinking water for a couple different reasons, according to the column. First of all, off-trail travel in thermal areas is not permitted, and the ground in thermal areas can be dangerous to traverse. Secondly, thermal waters can contain harmful microorganisms, such as a brain-eating amoeba called Naegleria, and elevated levels of arsenic and fluoride. The arsenic concentration in YNP’s thermal features is often about 1 milligram per liter, but has been found to be as high as 17 mg/L in certain samples. The Maximum Contaminant Level (MCL) for arsenic recommended by the Environmental Protection Agency (EPA) is 0.010 mg/L.
The second type of water discussed is non-thermal water from rivers and creeks. This water typically comes from snowmelt and rain, and is the best option for drinking. Non-thermal waters can still contain microorganisms such as E. coli or Giardia that should be removed by filtration, sterilized by chlorination or boiled before drinking.
The final type of water in YNP is mixed water: when a thermal feature flows into a clean, cool river or creek.
“Because of dilution, the concentrations of the nasty chemical components, including arsenic and fluoride, are often substantially less than the thermal waters,” wrote McCleskey. However, in some cases, the concentration of those chemicals in mixed water can still exceed the MCL, especially just downstream from thermal features. Backpacking filtration systems are unlikely to remove chemical components, and boiling the water does not lower the concentration.
Because the waters of YNP have been studied extensively over the years, some locations of potentially hazardous mixed water are known. YVO included a graphic which shows that the rivers closest to the major geyser basins are the most likely to contain high levels of arsenic.
“When looking to top off your [water] supply, ask yourself, ‘where does the water come from and is there a thermal area upstream?’ Whenever possible, choose a river or stream without thermal waters draining into it,” McCleskey wrote.
