THERE IS RADIUM IN PRIVATE WELLS IN MINNESOTA

Radium (Ra) is a naturally occurring radioactive element that occurs in parts of Minnesota groundwater, most often found in quartz sandstone aquifers. Testing for Radium in private wells is not required nor is there much information about it relating to private wells. Drinking water with elevated radium over long periods of time can increase a person’s risk of cancer. For public water supplies, the Environmental Protection Agency (EPA) has a maximum contaminant level (MCL) for combined radium 226/228 of 5 pCi/L. Gross alpha is a good indicator of radioactivity in groundwater, detecting alpha particles released in certain decay series. Radium-226 is an alpha emitter and the most common isotope in groundwater.

This study aims to answer:

1. If radium is detected in private wells and at what concentrations.
2. Whether a public water supply well a good indicator that private wells in the area may also have elevated radium.
3. Whether gross alpha a good indicator for radium in drinking water.

This investigation selected five regions throughout Minnesota. Each study site is centered around public water supply wells that have combined radium 226/228 concentrations above 5 pCi/L. In round one, approximately 20 private wells were selected near a public water supply well in each study site, with similar aquifer and/or well depth as the public well. Private wells were sampled for gross to determine if there were any radioactive signature in the groundwater. In round two, any private well with gross alpha above detection was resampled for combined radium 226/228. There was a total of 97 wells sampled in round one and 48 wells resampled for combined radium 226/228 in round two. Of the wells analyzed for gross alpha; 53 of the 97 (55%) wells had some detectable level of gross alpha. In round 2, 44 of the 48 (92%) wells had combined radium 226/228 above detection and 12 wells (25%) above the MCL. Gross alpha did not have to be elevated above the MCL for combined radium 226/228 to be above 5 pCi/L.

The results show radium was detected in private wells and can be elevated above the MCL for combined radium 226/228. Public wells with radium 226/228 may be a good indicator that radium may occur in nearby private wells. Gross alpha may indicate the presence of radium and be a good screening tool for private well users.