USGS Analyzes Idaho Groundwater Data to Optimize Future Aquifer Monitoring

IDAHO FALLS, Idaho — U.S. Geological Survey scientists today released analyses of more than 30 years of water-quality data collected at the U.S. Department of Energy’s Idaho National Laboratory Site. The data reveal long-term trends toward improved groundwater quality in the eastern Snake River Plain aquifer. Those results will be used to optimize the aquifer monitoring network at the INL Site.

“The Idaho Cleanup Project at the INL Site is having a positive effect on the water quality of the eastern Snake River Plain aquifer,” said Roy Bartholomay, manager of the USGS INL Project Office. “The trend data from this study confirm that, and will help us to refine our monitoring efforts going forward.”

USGS scientists analyzed data collected from 99 wells at the INL Site between 1981 and 2012. The study focused on wells possibly affected by wastewater disposal that occurred from the early 1950s until the late 1980s at the INL Site. The data analyzed included concentrations of tritium, strontium-90, major cations, anions, nutrients, trace elements, total organic carbon, and volatile organic compounds.

Key findings include:

• Long-term trends in the concentrations of radionuclides such as tritium and strontium-90 show that improved wastewater disposal practices are helping to reduce concentrations of those constituents in groundwater.

• Concentrations of the inorganic compounds sodium and chloride are decreasing at wastewater disposal sites, but increasing farther downgradient in the aquifer. For example, chloride disposed of at the Idaho Nuclear Technology and Engineering Center in the mid-1990s has moved about 3 miles south where it was found at the highest concentrations in wells near the Central Facilities Area.

• Trend test results indicated an increasing trend for carbon tetrachloride, a volatile organic compound, at the Radioactive Waste Management Complex Production Well for the period 1987 -2012. However, trend analyses of data collected since 2005 show no statistically significant trend, indicating that engineering practices designed to reduce movement of VOCs to the aquifer may be working.

An upcoming USGS study will apply these water-quality trend data to statistically optimize the monitoring well network at the INL Site. That process could identify wells that could be eliminated from the network, thereby reducing overall network costs.