Technology Description

Stable isotope ratio analysis is an analytical approach that has been widely used for understanding the geochemical behavior of naturally occurring compounds in the environment. This field of study relies on the fact that the major elements composing the inorganic molecules of interest to geochemists (e.g., C, N, S, O, H, Cl) occur as isotopes that can be quantified using isotope-ratio mass-spectrometry (IRMS). Moreover, the ratio of the specific isotopes in a given compound (e.g., ¹⁵N/¹⁴N  in NO₃ or ¹⁸O/¹⁶O in H₂O) can be used to track the source of that compound (e.g., nitrate formed in the atmosphere versus that formed during nitrification in soils) as well as to quantify the compound's fate in the environment (e.g., nitrate affected by microbial reduction). This project is a collaborative effort among scientists at the University of Illinois at Chicago, Environmental Isotope Geochemistry Laboratory, the U.S. Geological Survey (USGS) in San Diego, California and Reston, Virginia, and Shaw Environmental. Inc. in Lawrenceville, New Jersey. These researchers will utilize compound-specific stable isotope analysis methods recently developed for Cl and O in perchlorate, as well as analysis of radioactive ³⁶Cl in perchlorate to evaluate regional sources of this anion in RCF-area groundwater. For several large supply wells containing perchlorate in the RCF area, coupled well-bore flow and depth-dependent water-quality data will be collected under pumping conditions to directly measure the vertical distribution of flow and perchlorate into these wells from the local aquifer. For broadly screened wells, this technique can provide important information concerning depth at which perchlorate enters the well screen. Such data have forensic importance since mixing of different water sources within a well can be evaluated and contamination sources apportionated. Additional geochemical analysis and groundwater dating techniques will be utilized during this effort. At the conclusion of this project, a summary will be prepared concerning the origins of perchlorate in groundwater throughout the RCF region.