Assessment of New Calculation Method for Toxicological Sums-of-Fractions for Hanford Tank Farm Wastes [report]

Lenna A. Mahoney
2006 unpublished
1 The Environmental Simulation Program (ESP) is a registered trademark of OLI Systems, Inc., Morris Plains, New Jersey. 2 Here "layers" has the same meaning as the word "components" that is used in BBI terminology. iv analyses and the variability of concentration within the waste. The overall uncertainty might be considerably greater in tanks that have not been sampled. A detailed though semi-quantitative study was made to learn the reasons for method-related changes in SOFs at TEEL-3. This
more » ... level was chosen because new-method SOFs differed from old-method values somewhat more than at the other TEEL levels. Three aspects of the change in SOF calculation method were the causes of significant changes (those exceeding 30%) in liquid-phase SOFs for TEEL-3: • In 16 of the 24 tanks in which significant increases occurred, the primary cause was differences between the ESP-predicted and BBI solubilities of analytes (most often NO 3 , NO 2 , OH, and Al). This was also the primary cause of the major decreases in liquid SOFs, which occurred in 14 tanks. • In 3 of the tanks in which significant increases occurred, the primary cause was the use of analyte concentrations from the maximum-SOF layer instead of the tank-average waste. • In 5 of the tanks in which significant increases occurred, the primary cause was the increase in the effective toxicity of TOC that resulted from using oxalate to represent all TOC. Several aspects of the change in SOF calculation method were the causes of significant changes (those exceeding 30%) in wet bulk solid SOFs for TEEL-3: • In 37 of the 45 tanks in which significant increases occurred, the primary cause was the use of the concentrations of the layer that had the maximum SOF in the tank instead of the tank-average waste. • In all 5 of the tanks in which significant decreases occurred and in one of the tanks that showed an increase, the primary cause was solubility changes (ESP versus BBI). • In 4 of the tanks in which significant increases occurred, the primary cause was an increase in the effective toxicity of lead because of its assignment to the compound lead hydroxide. • In 2 of the tanks in which significant increases occurred, the primary cause was an increase in the effective toxicity of TOC because of its assignment to oxalate. • In one of the tanks in which significant increases occurred, the primary cause was adjustments made to the ESP compositions in the old method. Taking the results for liquid and wet bulk solids SOFs together, it is clear that the use of the maximumlayer approach was the dominant reason why the new method calculated different (in particular, larger) SOFs than the old. This maximum-layer approach was chosen to be consistent with the approach used in calculating ULDs for radiological assessments, and led to a change in the direction of conservatism. Differences between ESP and BBI solubilities were the next most common reason for differences between new and old SOFs, particularly in the liquid phase. The solubility-related changes in SOF were roughly equally distributed between increases and decreases. No general statement can be made about whether ESP modeling (as in the old method) or direct use of BBI data provides more accurate results; there were examples of both. Changes in the effective toxicities of TOC and lead were the third most common reason. These toxicity changes increased SOFs and so were in a conservative direction. Although decreases in Ca and Al toxicity decreased the new method SOFs for a few tanks, in no case did they cause the new-method SOFs to be significantly lower than those generated by the old method. v
doi:10.2172/894482 fatcat:3xix43ud2zh2pffnyjz7zzvnte