Abstract
Underground water represents a large portion of the available water supply, and the determination of the rate and direction of ground-water flow by the utilization of tracers provides knowledge that is useful in evaluating the water inventory of an aquifer. Such knowledge is also useful in the planned discharge of waste products into the ground. A tracer moving through a porous medium is subjected to ion exchange and adsorption. The amount of ion exchange and adsorption of certain radioactive tracers can be reduced by the process of chelating the radioactive tracer with ethylenediamine tetra -acetic acid. As radioactive isotopes can be detected in low concentrations they are well suited as ground-water tracers because such low concentrations will not modify the properties of the ground water or of the aquifer. Antimony-124, cerium -141, chromium -51, indium -114, ruthenium -103, and strontium -85 in chelate form were tested in vertical exchange columns filled with 20-30 mesh crushed illitic shale having an exchange capacity of 19 meq /100 gms. The elution curves for the chelated radioactive tracers w ere compared to the elution curves of chloride pulses. Of the six chelated radioactive isotopes tested, chromium -51 is apparently the best tracer. In the shale -filled exchange columns chelated chromium -51 moved through the columns at a velocity of about 96 percent that of the chloride ion. Unchelated chromium -51 failed to elute from the exchange column with the passage of 9- 4 pore volumes of eluting solution through the column. Distribution -coefficient determinations were made under static conditions for the chelated radioactive tracers, and comparison of the values for static conditions with the distribution -coefficient values determined from the exchange column data shows that close agreement exists between the distribution -coefficient values. It is possible to predict the elution history of an exchange-column experiment by making distribution -coefficient determinations under static conditions. Experimental data indicate that it would be possible to determine the water velocity within an aquifer by determining the arrival time of a chelated radioactive pulse peak in an observation well rather than by relying upon the time of the first appearance of the tracer in the observation well. Such an analysis would give the average tracer velocity; whereas, use of the first arrival time gives the greatest tracer velocity.
Jennings, Albert Ray (1964). Evaluation of selected radioisotopes as ground-water tracers. Doctoral dissertation, Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -173987.