The final disposal of sewage using submarine outfalls has become an actual solution for coastal cities all over the world. In order to get the best results it is necessary to carry out specific studies for the proper design of the outfall. Dilution and decrease in bacterial concentrations are two key aspects for the design. Radioisotope tracers have been used extensively in studies performed in some Brazilian waterbodies where outfall systems exist or are to be installed. As far as dilution measurement is concerned, both point and continuous radiotracer injections can provide useful results. The T90 measurements can be better accomplished using a combined tracer technique for sampling the sewage field, using the radiotracer for dilution measurement and rhodamine B as a visual aid. Typical results of dilution measurement using both techniques mentioned, as well as a summary of T 90 results obtained for the Santos, Fortaleza and Maceió outfalls are presented.
