Scott F. Korom¹ and John C. Seaman²

¹Department of Geology and Geological Engineering, University of North Dakota, 81 Cornell Stop 8358,
Grand Forks, ND 58202-8358
²Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802

Introduction: It is too common in the groundwater profession to read of studies that add anions as tracers to groundwater, most commonly bromide (Br^–) and chloride (Cl^–), label them as “conservative” or “non-reactive,” and apparently assume they are. Br^– and Cl^– are relatively safe, easily detected, and inexpensive—all important attributes of tracers (Davis et al. 1980), which apparently explain their popularity. But are they conservative? Davis et al. (1980, 14) described the conservative behavior of an ideal tracer as “moves with the water, . . . is chemically stable for a desired length of time, . . . and, for most purposes, is neither filtered nor sorbed by the solid medium through which the water moves.” Davis et al. (1980, 22) endorsed the use of anionic tracers, calling them “particularly useful because of their low susceptibility to adsorption or ion exchange processes on natural aquifer materials.” However, they (Davis et al. 1980, 15) also warned, “Failures of tracer tests are also caused by a lack of understanding of the hydrologic system.”

SREL Reprint #3238