This presentation describes the detailed laboratory tests of biofiltration media that is being considered for use in engineered stormwater treatment systems recently proposed for a large field laboratory testing site in the southwestern United States. These stormwater treatment systems were designed to treat 90% of the long-term runoff volume from drainage areas ranging from 5 to 60 acres at the site. The pollutants of interest for the project include cadmium, copper, lead, and dioxins, and the effluent concentrations had to meet design criteria that are based on numeric effluent limits that are applied to stormwater discharges through the site's NPDES permit. An additional feature of the project is that existing runoff concentrations for the pollutants of interest are generally below levels typically seen in urban and industrial stormwater runoff, therefore the tests needed to simulate site-specific conditions by adjusting raw influent samples to representative, where possible. The media tested vary widely in terms of cost, performance, and maintenance requirements. However, because of the large volume of media specified for the proposed designs, unit volume cost savings (during construction) are potentially significant if media volume and types can be optimized. Furthermore, the potential for long-term cost savings is also significant, and therefore this study also considers life-cycle costs (e.g., media replacement frequency) and maintenance problems (e.g., clogging frequency). This optimization activity should result in improved predictions of life-cycle costs, of pollutant removals over the media's lifespan, and of maintenance issues and intervals, and should result in improved design and performance when installed in the field.