This report documents an evaluation of the model performance stratified by six stability classes, three wind speed classes, and three mixing height classes. The model accuracy is found to be dependent on stability class. For stabilities A and B, the model shows some tendency to overestimate concentrations, especially near the plant. For stabilities D, E, and F, the model greatly underestimates concentrations at all but the most distant sampler. For stability C, the model tends to agree with the measurements. Higher wind speeds result in a trend toward overestimates at the Muskingum plant, and a trend toward underestimates at the Canal plant. For the Canal plant, there does not appear to be a definite pattern between the accuracy of the model estimates and mixing height. However, at the Muskingum plant, large underestimates occur for the lowest mixing height class. This implies that the model is treating the plume as penetrating the top of the mixed layer (with resulting concentration estimates of zero) more frequently than actually happens.

Prepared by GCA Corporation, GCA Technology Division, Bedford, Mass., under contract no. 68-02-1376, task order 23. Includes bibliographical references (p. 47).

v. 1. Time-concentration relationships. -- v. 2. Testing and evaluation of model improvements. -- v. 3. Further analysis of modeling results.