This research project evaluates and enhances a novel stormwater control measure for heavy metals called the Biomat. The water quality effects of Biomat treatment on a field scale were examined. Dissolved Pb and Cu were major contaminants, found in roof runoff at mean values of 2.7 mg/L Pb and 0.8 mg/L Cu at the research site. Biomat treatment reduced concentrations to mean values of 30 mcg/L Pb and 13 mcg/L Cu. Results indicate that an approximate steady-state concentration was reached for dissolved metals. This concentration appears to result from equilibrium between native metals on the media and metals dissolved in stormwater. Water quality results from a second site where influent metals concentrations were significantly lower (mean influent Pb at 15 mcg/L, Cu at 9 mcg/L) supported this hypothesis. Further water quality improvement was achieved with an additional aluminum-based water treatment residual and sand media, focusing on phosphorous.