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1 Summary Evaluation of the effectiveness and life cycle cost of using ferric oxide (iron) media applied in full scale systems to promote dissolved metals removal from natural highway stormwater runoff was the primary objective of this study. Monitoring conducted in 2017 and 2018 at an existing swale-type and a vault- type full scale ferric oxide-sand filter constructed in Maplewood, Minnesota, demonstrated that ferric oxide can effectively remove several dissolved and particulate metals. The ferric oxide filters were able to remove dissolved lead, copper, chromium, arsenic, zinc and iron. Dissolved nickel was not effectively removed by either filter. Dissolved metals removal for the two sites ranged from 47 to 49 percent for arsenic, 17 to 81 percent for chromium, -57 to 41 percent for chromium, 16 to 53 percent for lead, -504 to -19 percent for nickel, 70 to 85 percent for zinc, and -93 to 84 percent for iron. For each metal, percent removal was greater for the Highway 36/61 ferric oxide filter compared to the Woodlynn Avenue filter and this was likely a function of larger filter bed to watershed area ratio for the highway 36/61 treatment cell. Particulate metals were also removed with measured total metals removal ranging from 54 to 72 percent for arsenic, 79 to 81 for chromium, 26 to 69 for copper, 90 to 92 percent for lead, -102 to 28 percent for nickel, 83 to 93 percent for zinc, and 73 to 82 percent for iron. Total metals removal were more commensurate for the two study sites. A deterministic approach is provided to guide sizing ferric oxide-sand filter bed area and above-bed storage such that metals removal targets can be met while minimizing the potential for filter bed fouling caused by low dissolved oxygen. Inputs required include a continuous runoff record for the watershed tributary to the proposed site, hydraulic conductivity of the filter bed, estimation or direct measurement of ultimate biological oxygen demand, runoff temperature, and metals concentrations. An example is provided to demonstrate the use of a previously developed life cycle tool (Taylor et al., 2014) to calculate life cycle costs for proposed ferric oxide-sand filter systems. The example, which was based upon the Highway 36/61 ferric oxide-sand filter evaluated as part of this study, also demonstrated that the life cycle cost of a ferric oxide-sand filter was equivalent to or less than a standard sand filter when the greater metals removal performance of the ferric oxide filter was taken into account. A laboratory study was conducted to evaluate dissolved metals removal for open graded friction course (OGFC) with ferric oxide media incorporated into the pavement porespace. Greater than 50 percent removal was achieved for uncorrected tests conducted with granite and quartzite OGFC. This laboratory program was intended as a âproof of conceptâ as there are no literature available regarding the use of ferric oxide in asphalt pavements and thus the effect of ferric oxide on the mechanical performance in terms of rutting, fatigue, and thermal cracking of open-graded mixtures is unknown. Full scale testing is needed before widespread application.
