title: Assessment of existing roadside swales with engineered filter soil: II. Treatment efficiency and in situ mobilization in soil columns.
abstract: Use of roadside infiltration systems using engineered filter soil for optimized treatment has been common practice in Germany for decades, but little documentation is available regarding their long-term treatment performance. Here we present the results of laboratory leaching experiments with intact soil columns (15 cm i.d., 25-30 cm length) collected from two German roadside infiltration swales constructed in 1997. The columns were irrigated with synthetic solutions of unpolluted or polluted (dissolved heavy metals and fine suspended solids) road runoff, as well as a soluble nonreactive tracer (bromide) and a dye (brilliant blue). The experiments were performed at two irrigation rates corresponding to catchment rainfall intensities of approximately 5.1 and 34 mm/h. The bromide curves indicated that preferential flow was more pronounced at high irrigation rates, which was supported by the flow patterns revealed in the dye tracing experiment. Nonetheless, the soils seemed to be capable of retaining most of the dissolved heavy metals from the polluted road runoff at both low and high irrigation rates, except for Cr, which appears to pass through the soil as chromate. Fluorescent microspheres (diameter = 5 μm) used as surrogates for fine suspended solids were efficiently retained by the soils (>99%). However, despite promising treatment abilities, internal mobilization of heavy metals and P from the soil was observed, resulting in potentially critical effluent concentrations of Cu, Zn, and Pb. This is mainly ascribed to high concentrations of in situ mobilized dissolved organic carbon (DOC). Suggestions are provided for possible improvements and further research to minimize DOC mobilization in engineered filter soils.
authors.affiliation: Department of Agriculture and Ecology, University of Copenhagen, Frederiksberg C, Denmark. sti@life.ku.dk
authors.forename: Simon T
authors.initials: ST
authors.lastname: Ingvertsen
authors.forename: Karin
authors.initials: K
authors.lastname: Cederkvist
authors.forename: Marina B
authors.initials: MB
authors.lastname: Jensen
authors.forename: Jakob
authors.initials: J
authors.lastname: Magid
mesh_terms: D001336:Automobiles; D001965:Bromides / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D003247:Conservation of Natural Resources; D003252:Construction Materials; D004738:Engineering; D004784:Environmental Monitoring; D005858:Germany; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001965:Bromides; D019216:Metals, Heavy; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D014867:Water; D010758:Phosphorus; D002244:Carbon