In environmentally conscious design of chemical processes, environmental assessment is applied system atically during each of the different stages of the conceptual design process to help select options that are benign from an environmental perspective. Nevertheless, deviations from the design conditions over the course of operation of the industrial plant may compromise the environmental performance that was initially forecast, causing environmental damage liable to compensation. This paper presents an alternative method for assessment of chemical processes that is based on utilization of an index called the Environmental Return Time-ERT. This index represents, for a given set of design conditions, the time needed to compensate for predictable environmental damage and return to an acceptable level of environmental quality. A case study is used to demonstrate application of the proposed method to a stage of the conceptual design phase of a process for production of benzene by hydrodealkylation of toluene (the HDA process). In this case study, the design conditions for the conversion reaction and for the gas purge fraction of the process that will enable an ERT <= 1 to be achieved are defined. This exercise, based on selection of alternative design options from an environmental perspective, leads to the conclusion that utilization of the ERT index enables choice of environmental quality criteria with lower subjectivity than utilization of absolute values for potential environmental impacts. The study's results also include prediction, during the design phase, of the operational conditions and the time operating under these conditions necessary to compensate in advance for the environmental damage that is likely to occur during the life cycle of the operation.