Mass balance analysis at each sampling point provided an internal
validation for the study by accounting for the disposition of radioactivity found as 14C-volatiles in the sorbent, 14CO2 in KOH traps, and 14C activity in the water and sediment (extractable and non-extractable). Demonstrating that the total radioactivity at each sampling point is greater than 90% provides assurance that all of the activity is accounted for and appropriately characterized.