Increasingly, sustainability is a major consideration in decision-making processes and the implementation of remediation strategies. There are a number of initiatives from international and national organizations to develop sustainable remediation frameworks that aim to balance the environmental, social and economic impacts, both positive and negative, while removing unacceptable levels of risks to human health, water, soils, biodiversity and other receptors of concern (Rizzo et al., 2016). These frameworks also include stakeholder involvement and a mechanism for assessing the sustainability of a particular remediation strategy. Sustainable remediation is now covered by the International Organization for Standardization with ISO standard 18504:2017 “Soil quality – Sustainable remediation” (ISO, 2017). In the United States of America, ASTM International (formerly American Society for Testing and Materials) has developed a standard “Standard Guide for Greener Clean-ups ASTM E2893 - 16e1” (ASTM International, 2016).
The procedures for the selection and implementation of strategies to remediate polluted soils are often prescribed in national legislation and supported by guidance documents and frameworks. The national frameworks are generally similar and have the following components.
The remediation objectives will include the desired specification of the soils following remediation, including target levels for the contaminants, and the intended future use of the site. The future use of the site is a major factor in the risk assessment. The process to define the remediation objectives will involve an investigation and characterization of the site and the contaminants, the development of a conceptual site model, and engagement with the regulator and stakeholders. Many national frameworks use a generic of site specific risk assessment and risk reduction approach to determine the remediation objectives (NICOLE and Common Forum, 2013). Other frameworks set two concentration levels for contaminants, a target level and a level above which action is required to remediate the soil. For each contaminant, there may be different levels for agricultural, residential and industrial land uses. In addition, it will be necessary to identify the organizations that will fund the eventual costs of the remediation. Under the “polluter pays” principle, this would include those responsible for causing the pollution or the current owner of the land. For cases where the individual or organization responsible for the pollution cannot be identified or is unable to pay for the remediation, national governments may need establish alternative funding mechanisms.
The remediation strategy should be designed to achieve the remediation objectives and should take into account regulatory considerations, assessment of the technology options, risk assessments, and operability studies, cost-benefit and sustainability analysis. Spatial heterogeneity of a polluted site can require separate remediation strategies for different zones. In some cases, the combined application of more than one technology can increase the success of the remediation strategy. Once the technologies have been selected, a detailed remediation action plan should be developed along with supporting elements such as a detailed budget; a procurement plan; a site-specific health, safety and environmental management plan; standard operating procedures; a waste disposal plan; and a monitoring plan. As many of the technologies are site and contaminant specific, it may be necessary to undertake pilot trials to ensure the strategy is effective before confirming the strategy for full-scale implementation. Further engagement with stakeholders and regulatory approval could be necessary before implementation can proceed.
Appropriate project management is required to ensure that the remediation strategy is implemented safely and effectively. The strategy should be monitored throughout its implementation to ensure that it is effective in achieving the remediation objectives. Where monitoring identifies divergence from the anticipated remediation outcomes, it may be necessary to review and adjust the strategy including selecting alternative technologies or agreeing to revised remediation objectives with the regulators.
Once monitoring has confirmed that the remediation objectives have been achieved, the operations can be completed and the site becomes available for the use that was determined in the remediation objective. For remediation technologies that require a long time to complete or only sequester the contaminants, it may be necessary to institute a long-term verification monitoring plan and designate responsibility for the future care of the site.
Further details on the procedures to be adopted to address a polluted site may be available within national regulations and guidance documents. As an example, Australia has developed a National Remediation Framework and technical guidance to support its legislation on polluted sites (CRC CARE, 2019). The technical guideline on soil washing includes a flowchart of the remediation steps which is shown in Figure 2 below. The United Kingdom of Great Britain and Northern Ireland Sustainable Regeneration Forum (SuRF-UK) published its framework assessing the sustainability of soil and groundwater remediation that linked to British national legislation3. The national legislation is based on three steps: risk assessment, options appraisal, and implementation of the remediation strategy (SuRF-UK, 2010). Canada also has guidance on approaches for addressing polluted soil and their sustainability that have often been referenced by other countries without such frameworks45.
FAO’s Environmental Management Tool Kit Series Volume 5 (FAO, 2020a) also provides tools for: polluted site identification and prioritization; preliminary risk assessment and design of detailed site investigation plan; and data analysis and generic quantitative risk assessment. Volume 6 (FAO, 2020b) provides tools for: risk reduction strategy design; risk reduction implementation; development of risk mitigation plans; and development of the environmental management plan.