The advent of computer-based modeling tools has greatly improved the ease with which biological process modeling can be implemented. However, the calibration of a site-specific model does not always receive the same level of scrutiny as does model development. Three examples are presented to illustrate how this can be detrimental to process design: (i) lack of solids mass balance closure can lead to erroneous SRT estimates, (ii) incomplete specification of COD partitioning can result in underestimation of plant solids loading and corresponding under-design of clarification and aeration capacities, and (iii) inadequate determination of nitrogen species and COD partitioning can hinder process design of nutrient removal facilities with stringent discharge criteria. Provision of these types of data will greatly facilitate model calibration and improve their utility.