Reclamation research is increasingly finding that homogenous topsoil depth requirements, originally developed in an agricultural context, are not always best suited to match the natural heterogeneity of the ecosystems reclamation practices aim to re-establish. Thick placement of topsoil may even be counterproductive if the species being planted are not adapted to rich soil conditions.  

To date, most research on this topic has centered on reclamation of larger scale mine sites; less work has been done on smaller scale sites such as in situ and conventional oil and gas sites. The NAIT Centre for Boreal Research, supported by ConocoPhillips, recently initiated a 15-year study that focuses on applying this principle to smaller scale industrial disturbances.

Four years into the study, no measurable differences in survival and growth of tree and forb species have been found between shallow and standard topsoil depth treatments. These results indicate that allowing operators to vary soil cap depth and to use topsoil where it is most needed may improve reclamation outcomes on smaller sites as well. Read more in the 2024 COSIA Report.

Lean oil sands – mine overburden containing naturally-occurring petroleum hydrocarbons (NPHCs) – are often used as a capping material during mining reclamation. However, using lean oil sands as capping material brings NPHCs closer to the surface than in undisturbed landscapes, so industry must take measures to mitigate the risk of negative impacts on surrounding ecosystems. 

Building on both research and expert consultation, the 2018 Lean Oil Capping Synthesis (project code: LJ0305) developed a Literature Review, a Field Program and Analysis Report, a Conceptual Site Framework document and a Risk Assessment Matrix document to provide industry members with guidance on capping thickness, cover design and risk assessment approaches.  

Overall, this project provided evidence to support adjustments to soil capping depth requirements. This has important implications for reclamation – allowing for variation in soil capping depth means operators can place soil where it is most needed to improve a project’s overall chance of reclamation success. Read more in the 2019 COSIA Mine Report or inquire internally to access the project’s Conceptual Site Framework and Risk Assessment Matrix documents.

Several COSIA studies (project codes: LJ0010, LL0146, LL0160 and LL0025) have determined that the inclusion of coarse woody debris in soils on reclamation sites has many ecological benefits: erosion control, improved seed and moisture retention, increased soil organic matter and nutrient cycling, and overall enhancement of long-term ecosystem recovery and biodiversity.

Along with other innovative treatments such as mounding, rough and loose soil placement and planting of site-selected mixes of trees and shrubs, coarse woody debris use is now widely recognized as a best management practice in boreal forest reclamation. Investment by COSIA has helped clarify the role of coarse woody debris in reclamation and promote its adoption and use.

Both salvaged peat and forest floor material are used as cover soils in reclamation following oil sands mining. However, they differ in physical properties and soil biological activity. The Aurora Soil Capping Study, a multi-disciplinary, collaborative field study (project codes: LJ0201, LJ0099, LJ0100 and LJ0219) involving research scientists from the University of Alberta and University of Saskatchewan, with the support of Syncrude, explored how tree seedlings on upland boreal forest restoration sites responded to different properties associated with these two soil cover treatments. 

Seedlings were found to grow better when forest floor material was used for soil capping compared to peat. Forest floor material caps provided a higher availability of key nutrients, warmer spring rooting conditions and better drainage. Another key result was that shallow forest floor material soil capping supported tree seedlings just as effectively as deeper capping. With peat, using thicker capping actually impaired tree seedling growth. Paired with other recent studies supporting the strategic use of shallower soil capping in reclamation, this research contributed to significant changes in capping depth requirements.  

Many additional findings relevant to informing industry best practices can be found in this project’s Final Cumulative Study in the 2019 COSIA Mine Report, which also lists the numerous peer-reviewed journal articles, theses and reports published between 2013 and 2019 as a result of this research.

Ongoing monitoring is necessary to confirm reclaimed sites are on a path towards meeting end land use targets. However, cost-effective tools to monitor reclamation trajectories are lacking. A recent COSIA study at Imperial’s Cold Lake Operations (project code: LJ0294) explored a novel monitoring method – the use of soil eDNA to assess the status and trajectory of reclamation sites. 

This study found that biological communities in sites reclaimed using modern methods showed more similarity to communities in reference (undisturbed) sites than to sites restored using older methods. Furthermore, specific types of fungi and metazoans were identified as potential bioindicator species, consistently being observed in reference sites and seeming to emerge over time in reclaimed sites. 

These results could help pave the way for the development of useful new DNA-based reclamation monitoring tools. Read more in the 2021 COSIA In-Situ Report.

Sandy a and b ecosites often have limited organic surface soil available for reclamation, so there is interest in exploring the use of other soil layers, with or without further amendments, as surface soil. This COSIA study (project code: LL0066) looked at the use of Bm or B/C soil horizons as topsoil in sandy ecosites. 

Four B horizon treatments with varying phosphorus and pH levels, and four other soil treatments (peat/mineral, forest floor/mineral, subsoil > 1 m, and tailings sand) were treated with no fertilizer (control), phosphorus and potassium (PK), nitrogen (N) and all three (NPK), then planted with aspen and fireweed in a greenhouse study. 

It was found that B horizon soils offer a viable surface soil when fertilized, and that the NPK fertilizer yielded best results. Without fertilizer, organic surface soils supported better plant growth, and researchers warned this contrast may be greater in field conditions due to the low water-holding capacity of soil with low organic content. Read more details in this peer reviewed journal article.

Disposing of organic wastes is an ongoing cost for oil sands operations, often necessitating hauling organic wastes long distances to landfills or sewage lagoons. COSIA member companies have identified that organic wastes could be a valuable fertilizer to enhance reclamation activities. 

The application of biosolids, a high-nitrogen organic fertilizer composed of treated, de-watered sewage sludge, was trialed during mine reclamation at Highland Valley Copper in BC (project codes: LJ0166 and LL0197). Biosolid use was found to improve vegetation production, enhance soil quality and fertility and increase soil water holding capacity. Overall, biosolids were more effective for building soil organic matter than traditional inorganic fertilizers. 

A further study in Alberta (project code: LE0040) identified an efficient in-vessel composting method that could result in financial savings within a short time period while also producing a useful biosolid product for reclamation.  In an agricultural context, the City of Calgary’s Calgro Program has been using treated municipal waste in farming applications for decades.  

Strong potential exists for biosolids, provided by camp waste composting and/or municipal sewage treatment plants, to be an asset in oil sands reclamation.  Read more about the use of biosolids at Highland Valley Copper or inquire internally to access other related materials for all three projects.

New fluid tailings produced by oil sands projects are required to reach a ‘ready-to-reclaim’ state –treated, placed in final location, and meeting performance criteria for final stages of reclamation – within 10 years of the end of a mine’s life (Directive 085, Alberta Energy Regulator). Achieving this necessitates different reclamation strategies for different tailings types. The greenhouse trial (project code: LJ0341) described here focused on thickened tailings capped with varying depths of peat mineral mix, all salvaged from Imperial’s Kearl Operations. The thickened tailings capped with peat mineral mix were then planted with upland or wetland boreal plant species. 

Researchers found that a thin (10cm) peat mineral mix cap over thickened tailings improved vegetation growth compared to uncapped thickened tailings. They also found that a 30cm peat mineral mix cap over thickened tailings improved growth even more. The thicker soil cap also better mitigated and delayed the oxidation of pyrite from the tailings materials, another key concern. These findings support requiring soil capping over thickened tailings, with deeper caps leading to better outcomes. 

Inquire internally to view the 2023 COSIA Report and other materials related to this project.