Spatial variability of a solid porous framework with regard to chemical and physical properties

Abstract

The spatial variability of physical, chemical and mineralogical properties of the unsaturated zone, thought to affect transport and degradation of organic pollutants, has been investigated at an experimental field site in the distal parts of the Gardermoen delta. The properties considered were saturated hydraulic conductivity ( K s), silt content, organic carbon (TOC), amorphous Fe- and Al-oxides, pH, Fe- and Al-associated phosphate, total inorganic phosphorus and minerals identified by XRD analysis. The unsaturated zone at the site studied was divided into five different sedimentary layers, two horizontal layers in the topset unit and three dipping layers in the foreset unit (coarse, fine and silty sand). Regarding the entire soil profile, amorphous Fe- and Al-oxides were positively correlated with TOC. TOC was also positively correlated with Al-P and Fe-P, both when considering the entire soil profile and only the subsoil. A weak positive correlation was found between the amorphous Fe- and Al-oxides and phosphate and the correlation was only significant when regarding the entire soil profile. The potential relation between soil chemical properties and a silty sand layer within the foreset unit was paid special attention. The distribution of silt and K s values were seen to be well correlated with the sedimentary structure. No relation between the soil structure within the foreset unit and the content of TOC and amorphous Fe-oxides was observed. Indication of an increased content of magnetic minerals within the silty sand layer was seen. Regarding phosphorus, a significant increase of total inorganic P was found in the silty sand layer due to small amounts of apatite within the silt fraction, while no relation between the soil structure and Fe- and Al-associated phosphate was observed. Hence, the silty sand layer does not seem to play any special role regarding the distribution of chemical soil properties that may affect plumes of organic pollutants.