Tracking pollution sources using stable isotopes
A landfill in an oil-producing region was known to have accepted industrial as well as muncipal waste. The industrial waste had a considerable component of smelter and oil-field waste, including tank bottoms. Therefore there was concern that heavy metals and radionuclides (from radium) had entered the groundwater system through unlined pits in sandy soil and had travelled to the site of surrounding domestic wells.
Defense contended throughout that monitoring wells on and around the landfill were drawing from a different aquifer than the domestic wells. We were able to show with oxygen isotopes that both sets of wells had water with the same isotopic composition and moreover that seasonal changes followed the same pattern in each. Therefore it was highly likely that the waters were the same and that contaminants found in both the domestic wells and the monitor wells had the same source.
Sulfur isotopes of sulfate dissolved in the water were then used to trace contaminants found in groundwater back to waste deposited in the landfill