Transport and retention of heavy metals in contaminated soil and groundwater : A case study from Pukeberg glassworks in Småland, Sweden

University essay from Stockholms universitet/Institutionen för naturgeografi

Abstract: As much as 80 000 sites, including landfills from glass production industries, are estimated to be contaminated in Sweden. One of these landfills is located near the glassworks factory of Pukeberg, in the municipality of Nybro, Southeast Sweden. It has been found to be severely contaminated with heavy metals, which have toxic effects to humans and biota. The aim of this study is to investigate hydrologic properties at Pukeberg, including groundwater velocities and their potential (spatial) heterogeneity that would affect the transport of metals. Metal concentrations in soil, pore water and groundwater were measured to investigate such metal transport and retention at the site. Slug tests were conducted at the site to determine local discharges and water velocities. For comparison, total groundwater flows through the landfill were estimated by considering water balances of the upstream catchment. Results showed a much higher groundwater flow through the landfill at Pukeberg when estimated from water balance constraints of the upstream catchment, compared to when up-scaled from local measurements of hydraulic conductivities and gradients within the landfill. This points to the existence of aquifer heterogeneity, including preferential flow paths and low-flow zones. Depending on flow path, transport velocities of heavy metals could therefore differ considerably. With a pH of 7 in pore water, and relatively low DOC (dissolved organic carbon) concentrations, environmental conditions were found likely to favour a strong retention for most of the metals investigated. This conclusion is supported by our estimates of Kd (the soil-water partitioning coefficient), derived from the in-situ ratio between soil concentrations and pore water concentrations at the landfill. These estimates were consistently higher than previously reported laboratory results from leaching tests, as well as guideline values from the Swedish EPA. For instance, Kd for Pb and As was found to be 50600 l/kg and 16400 l/kg, respectively. Thus, for most metals, a limited transport downstream could be expected. Indications of high aquifer heterogeneity within the limited area investigated in this study however give rise to uncertainties, for instance regarding the representativeness of the taken samples. Possible future analyses of extended sampling schemes could decrease these uncertainties.

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