A large-scale soil-mixing process for reclamation of heavily disturbed soils

- Crude oil-contaminated soil and thermally remediated soil were mixed with topsoil.
- Mixtures had representative values of physical, chemical, and biological parameters.
- The soil mixtures were homogenous spatially and with depth.
- Soil mixing may be a good way to jumpstart reclamation of disturbed soils.

Soil excavation associated with energy production or mineral extraction results in heavily disturbed landscapes that must be reclaimed to avoid long-term economic and environmental losses. A common practice in reclamation of these sites is topsoil replacement across the disturbed area. In some instances, this process requires importing topsoil from another location, known as topsoil transfer, which can be expensive and introduce a new seedbank, insect community, or plant pathogens. This research describes a soil-mixing process for disturbed soils that may be used to reduce costs associated with topsoil transfer and accelerate the recovery of soil function following a large excavation. This process was applied to two disturbed soils: i) crude-oil contaminated subsoil material; and ii) crude-oil contaminated subsoil material that was remediated using ex-situ thermal desorption. These soils were separately mixed with native, non-contaminated agricultural topsoil at 1:1 ratio (by volume). The native, disturbed, and mixed soils were characterized for soil physical, chemical, and biological properties, and statistics indicated that the mixtures were homogenous both spatially and with depth. However, the mixtures were significantly different from both the disturbed materials and native topsoil, primarily driven by changes in soil organic carbon, plant available nutrients, and biological activity. These results suggest that this mixing process can be used for soil reclamation at large-scale excavation sites to both reduce project costs and enhance recovery of soil parameters.