Stabilization of metals and metalloids in contaminated shooting range soils - the effect of iron-based amendmends

• Main Author: Grasshorn Gebhardt, Karl-Alexander Serge
• Format: Dissertation
• Language: English

Shooting range soils contain large amounts of copper (Cu), zinc (Zn), lead (Pb) and antimony (Sb) from spent bullets. They are sources of contamination for soil, groundwater and surface water, and may pose a risk to the environment and human health. The investigated shooting range at Steinsjøen (Hurdal, Norway) has surface and porewater concentrations exceeding EU drinking water limits and Norwegian environmental quality standards. Chemical stabilization with iron-based soil amendments has shown to be a promising method for sustainable remediation. A test field was set up at a shooting range bullet trap at Steinsjøen. The aim was to investigate the long-term retention effects of two different iron-based amendments. Different sections with reference soil (no amendments), soil with CFH-12&limestone (ferric oxyhydroxides and limestone for pH regulation), and soil with zerovalent iron (Fe) were established. Some sections contained 2%, some 4% amendments mixed in, and some contained amendments as top application (2%). Porewater samples were taken from July 2010 to October 2013 and analyzed. In addition, surface water was sampled in 2013. Examination of reference soil porewater indicated a constantly high weathering rate of spent bullets with high concentrations of Cu, Zn, Pb and Sb. The results showed that pH and DOC levels play important roles in element mobilization. Both amendment types showed good retention for Pb (>94%) in all soils with mixed in application. Antimony (59-74%), Cu (64-70%) and Zn (60-73%) retention in soil mixed with 2% CFH-12&limestone was lower than for Pb. The same was valid for Sb (~73%) and Cu (46-94%) in soil mixed with zerovalent Fe. Zinc retention was very low in the zerovalent Fe amended soil, even negative (-26-26%), probably due to a lower pH than in soil with added limestone and small Zn concentrations in the amendment itself. When adding 4% amendment, a retention improvement was only found for Sb (>85%). Top application did not show good results for any of the elements due to no downward movement of sorbents and had negative effects on cation retention in CFH-12&limestone treated soil probably due to ion exchange reactions with calcium (Ca). Geochemical modeling with Visual MINTEQ showed that approximately ~20% Pb was bound to fulvic acids containing phenolate (FA2) and ~70% of the Cu to fulvic acids containing carboxylate (FA1) in the reference soil. 100% of Pb and Cu in porewater from CFH-12&limestone treated soil formed com