This paper evaluates the validity of ISC -PRIME and ISC3 for modeling multi-tiered, sloped, porous structures. ISC- PRIME and/or ISC3 were proposed for use to model a pair of such structures that were to be located near two proposed combustion turbines. The local agency questioned the use of BPIP determined building dimensions as inputs to either model due to the complexity of the surrounding structures. Hence, wind tunnel testing was conducted to determine the equivalent building dimensions for ISC- PRIME and ISC3 input. During the course of the study, building dimensions were defined using both the BPIP analysis program and wind tunnel determined “equivalent building dimensions.” ISC- PRIME and ISC3 were then run for 36 wind directions and one wind speed using both sets of building dimensions as input. The predicted concentrations were compared with wind tunnel measurements obtained using a scale model of the facility. A statistical evaluation of ISC- PRIME and ISC3 predictions versus the wind tunnel observations was carried out to assess the adequacy of the standard modeling approach for this complicated situation versus the equivalent building dimension approach.