Naturally-occurring arsenic in groundwater in Missoula County
Arsenic occurs naturally in some rocks and sediments. The Health Department has compiled data on tests of private wells in Missoula County, and has identified three areas where arsenic is more likely to be elevated: The Blackfoot Valley, the Nine-Mile/Huson area, and the Lolo Creek area. Not all well water in these areas is impacted, so testing individual wells is required to determine if there is a problem with your water.
Sample results indicate that almost all public systems in Missoula County contain water that meets the drinking water standard for arsenic. If you have concerns about the quality of water from your public system, contact your water system operator and ask for a copy of the "Consumer Confidence Report". Privately-owned wells are not required to meet water quality standards, but we recommend that all well owners test their water for arsenic at least once or twice (in addition to annually testing for bacterial contamination and possibly other contaminants), to rule out elevated arsenic levels. There are effective treatment methods for removing arsenic from drinking water, if you determine that your water contains elevated arsenic levels.