ELEVATED URANIUM AND LEAD IN WELLS ON THE CROW RESERVATION, BIG HORN COUNTY - A POTENTIAL PROBLEM

U.S. Geological Survey NURE (National Uranium Resource Evaluation) and GWIC (Ground Water Information Center) data from the Montana Bureau of Mines and Geology data show wells with elevated U (uranium) and Pb (lead) in Big Horn County, Montana. Wells with elevated U and Pb might pose health risks if the designated use is for drinking water. The EPA national primary drinking water standard for uranium is 30 ug/L and 15 ug/L for lead. Values of uranium in the NURE data base exceed the standard in many wells in the county. The highest value is 404 ug/L located south of Reno Creek in a 12’ deep well near Interstate 90. Lead data in the NURE data base is questionable due to instrumentation problems at the time the data was analyzed. The GWIC data from the Montana Bureau of Mines and Geology also shows some elevated uranium and lead values in Big Horn County. The GWIC data for Big Horn County has 1286 entries recorded. Of these, 600 sites were tested for lead and 169 for uranium. The GWIC data base shows 102 wells that exceed the 15 ug/L value for lead, with 55 wells exceeding 80 ug/L, and the highest value is 585 ug/L. Most of these wells are monitoring wells that are proximal to the Decker mining area and may be related to the coal, especially the Tongue River member of the Fort Union Formation. The elevated uranium from the GWIC data base has a strong correlation with Tertiary and Pleistocene age gravels. Many of the high values in the streams and springs on a GIS (Geographic Information System) generated map of NURE data are in the Quaternary terrace deposits. Most wells on the Crow Reservation are only drilled in these shallow deposits and most were not tested for lead or uranium. The administration of wells drilled on the Crow Indian Reservation, Big Horn County, is by the Indian Health Service. Most of these wells are not reported to the GWIC. These wells may pose health risks if the primary use is for drinking water, further testing may be implicated.