The impacts upon the environment resulting from construction, stert-up, and operation of a gaseous dfffusion plant are described. Some of the impacts are typical regardless of location of the plant. Others are atypical and depend upon location; those are presented, by way of example, as they occur at the Portsmouth Gaseous Diffusion Plant. The various environmental contaminants that may be produced in the operating plant are described. The concentrations of those contaminants are stated; and the adverse biological effects of pertinent conteminants are elucidated. UF/sup 6/ may be enriched in the Portsmouth Gaseous Wffusion Plant to almost any /sup 235/U concentration desired. The environmental impact of the plant varies somewhat according to /sup 235/U concentrations. However, commercial plants are not expected to enrich /sup 235/U in concentrations greater than 4%. for this reason, environmental effects due to Portsmouth operations within that range are emphasized. The study revealed that present discharges from the plants generally have no detrimental effects upon the environment. (auth)