Bench Scale Development and Field Testing of a Partial Exfiltration Trench (Per) for Controlling Highway Runoff Quality

摘要

Design of in-situ control systems such as PER loaded by lateral pavement sheet flow requires data on partitioning and loading for effective treatment design. This project examined Zn, Cd, Cu and Pb partitioning, cumulative loadings and washoff of storm water pavement sheet flow from the I-75 experimental site, an urban inter state pavement site, typical of heavily traveled urban inter state highways. Results from partitioning analysis between the dissolved and particulate - bound fractions indicate that Zn, Cd, Cu and Pb mass can be predominantly dissolved in lateral pavement sheet flow at the pavement edge. High dissolved fractions can be attributed to low urban rainfall pH levels, relatively short pavement residence times and low pavement runoff alkalinity and hardness. Partitioning coefficients only approaching equilibrium towards the end of the events as metals partitioned to entrained solids. Plots of cumulative heavy metal mass as a function of elapsed runoff time demonstrate that for the duration of all events the dissolved fractions dominated the particulate fractions for Zn, Cd, Cu and Pb. In terms of delivery, results also indicate that the dissolved mass generally exhibited a disproportionate initial delivery in comparison to particulate mass. Results of this examination indicate that treatment of highway pavement storm water at the edge of the highway shoulder poses unique challenges due to the unsteady nature of processes including rainfall runoff, mobilization and partitioning of heavy metals, variations in storm water chemistry, residence time on the pavement and delivery of particulate mass.