"TRC Environmental Consultants, Inc; under contract to Occidental Oil Shale, Inc ., has conducted an evaluation of the performance of five Gaussian complex terrain models . The purpose of this effort is to satisfy a permit condition required by the Colorado Air Pollution Control Division to utilize meteorological and air quality data measured at Occidental's Logan Wash oil shale processing facility in a comparative assessment of model predictions . The five models tested were MPTER, COMPLEX I, COMPLEX II, COMPLEX I with modified terrain correction factors, and COMPLEX I employing an alternate plume height option. Both long-term (about 7 . 5 months) and short-term (hourly) average concentrations of hydrogen sulfide (H 2S) were computed by each of the models, the results from which were compared to actual measurements collected at Logan Wash during 1982 . Several statistical tests were utilized to facilitate the evaluation of the performance of these models. The results from these analyses indicate that these models are poor predictors of H 2 S concentrations at Logan Wash . The models demonstrated limited skill in predicting the magnitude, time, location, or frequency of peak pollutant impacts. This is not surprising because many of the assumptions that are implicit in these models are of questionable validity in complex terrain environments, so the results t hat they provide in such situations are , at best, of dubious value."