This test method is meant to allow for a rapid (24 h) index of a geomedia’sorption affinity for given chemicals or leachate constituents. A large number of samples may be run using this test method to determine a comparative ranking of those samples, based upon the amount of solute sorbed by the geomedia, or by various geomedia or leachate constituents. The 24-h time is used to make the test convenient and also to minimize microbial degradation which may be a problem in longer-timed procedures. While Kd values are directly applicable for screening and comparative ranking purposes, their use in predictive field applications generally requires the assumption that Kd be a fixed value.
While this test method may be useful in determining 24-h Kd values for nonvolatile organic constituents, interlaboratory testing has been carried out only for the nonvolatile inorganic species, arsenic and cadmium. However, the procedure has been tested for single laboratory precision with polychlorinated biphenyls (PCBs) and is believed to be useful for all stable and nonvolatile inorganic, and organic constituents. This test method is not considered appropriate for volatile constituents.
The 24-h time limit may be sufficient to reach a steady-state Kd. However, to report this determination as a steady-state Kd, this test method should be conducted for intermediate times (for example, 12, 18 and 22 h) to ensure that the soluble concentrations in the solution have reached a steady state by 24 h. Refer to Test Method D 4319 for an alternate procedure of longer duration.