Management of soil contamination at mine areas
Ulla-Maija Mroueh, Markku Juvankoski, Tommi Kaartinen, Jutta Laine-Ylijoki, Elina Merta, Jarno Mäkinen, Emma Niemeläinen, Henna Punkkinen & Margareta Wahlström, VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Finland.
On mine areas and their surroundings the background concentrations of metals or other minerals may be naturally higher than on other areas. Mining activities may also lead to transport of contaminants into soil surface waters and groundwater. Mineral particles, complexes or compounds can be released from solid materials, such as ore, waste rock, tailings and concentrate during excavation, transport and concentration as well as tailings areas. Typical transport routes include spreading by wind, and dispersion of leached components or particles with different mine waters. Formation of acid mine drainage is one of the most important causes of water pollution.
Other potential contaminants include oils and fuels, chemicals used in concentration processes and nitrogen compounds from explosives.
Legislative framework and Finnish national guidelines
On European level there is no uniform soil directive. Legislative provisions on soil contamination are included in some other directives and in national legislation, which may differ from country to country. The Directive on Industrial Emissions (IED 2010/75/EU) presents requirements to prevent soil contaminating emissions from large industrial plants. Mine Waste Directive (2006/21/EC) requires risk assessment of all mine sites. Other directives containing provisions against soil and water pollution include Water Framework Directive, Waste Directive, and Landfill Directive.
The framework of the Finnish environmental legislation is set in the Environmental Protection Act (527/2014). It forbids the contamination of soil and groundwater which may endanger human health or environment and presents general principles for prevention and monitoring of the environmental impacts of harmful substances. Permit requirements for remediation as well as licensing and supervisory authorities are also presented in the Environmental Protection Act and Degree.
Provisions on the assessment of the contamination and needs for remediation are laid down in the Decree on Contaminated Areas (214/2007). More comprehensive information can be found in the Guidelines on risk assessment and sustainable risk management of contaminated areas (Environmental Administration Guidelines 6 2014). The Memo of the ministry of environment on Waste classification of the excavated soil presents the principles and guidance on characterisation, treatment requirements and administrative procedures related to excavated soil. The Memo does not cover mine waste, for which the provisions are presented in the (190/2013). However, the Memo can be used as an additional guidance in planning of the utilisation of mine waste, when applicable.
Investigation and assessment procedure
The need for remediation should be assessed, when mine will be closed, in cases or accidental releases of hazardous chemicals to the soil and in other potential cases, where the spreading of hazardous compounds can endanger health or environment. In case of accidental releases the operator is obliged to inform the supervisory authorities. The Finnish legislation presents trigger (threshold) values for assessment of the need of soil remediation. On the areas where background concentrations are higher than threshold values, the background concentrations can be used as trigger values
The main stages of the site investigation and risk assessment procedure are the following:
- Collection of the available information (history, data from monitoring of site and the environment, background data) and preliminary assessment of the need for further investigations
- Planning of the site investigations for assessment of the size of the contaminated area and the level of contamination, including planning of sampling network, number and depth of samples, sampling methods, sample pre-treatment and laboratory analysis. In addition to soil sampling, other sampling may be needed for risk assessment, such as ground water, surface waters and biota. The investigations can be carried out in stages. Generally, in the second stage the focus is, after the preliminary risk assessment, to collect additional information needed for more detailed risk assessment.
To ensure representative sampling the planning of site investigations as well as the actual investigations should always be carried out in collaboration with experts on contaminated soil investigations.
- Site investigations in accordance on the investigation plan.
- Assessment of the need of remediation. In this stage the risk for human health and environment is assessed. The requirements of future use shall be considered in assessment.
- In the first stage of assessment the results of investigations are compared with local background values, national guide and limit values and other environmental quality standards. In Finland, the soil in industrial and traffic areas is generally classified as contaminated if the concentration of at least one compound is higher than upper guideline value. In other areas lower guideline values are used.
- If the guideline values and other environmental quality standards do not create sufficient basis for decision making, additional information can be produced by site-specific risk assessment. More information about the risk assessment on mine areas can be found e.g. from the report Improving Environmental Risk Assessments for Metal Mines: Final Report of the MINERA project (Kauppila et al. 2013) and from the Guidelines on risk assessment and sustainable risk management of contaminated areas (Environmental administration 2014).
- Reporting of the assessment of the need of remediation, including the site investigations and risk assessment as well as assessment of their representatives, quality assurance and reliability. The assessment report needs to be submitted to the responsible authority for approval.
- Approval of the assessment of the remediation need.
The objectives of the remediation of mine areas depend on the results of risk assessment, local conditions and future use of the area. The solution should also be sustainable, which means that the total benefits of the remediation should be maximised. The estimation of benefits is based on assessment of environmental impacts, cost and social aspects.
The first stage of the remediation is planning, which includes identification, assessment and selection of remediation methods. If the remediation is based on excavation of soil, the possibilities to utilise excavated soil should also be assessed. Before detailed planning and starting the remediation, the remediation plan needs to be approved by the licencing authority.
There are several potential methods that can be used for remediation of contaminated areas. They can be divided to in-situ, on-site and off-site methods. The selection of remediation method depends on the objectives of remediation, technological suitability for treatment of the contaminants on the site, cost and sustainability aspects, time available for remediation, etc. Some examples of methods that are typically used, include:
- excavation of the soils either for treatment or for transport to disposal areas
- soil washing
- thermal desorption
- natural attenuation or in-situ bioremediation
More information on remediation methods can be found on reviews and remediation technology catalogues, such as:
- Federal Remediation Technologies Roundtable (FRTR). Remediation technologies screening matrix and reference guide, Version 4.0. https://frtr.gov/matrix2/top_page.html
- Mroueh et al. 2004. Management of remediation of contaminated soils (Pilaantuneiden maiden kunnostushankkeiden hallinta). In Finnish. VTT Research Notes 2245.
- Khan et al. 2004. An overview and analysis of site remediation technologies. Journal of Environmental Management 71 (2004) 95–122
Kauppila T. et al. 2013. Improving Environmental Risk Assessments for Metal Mines: Final Report of the MINERA Project. GTK Research report 199. http://tupa.gtk.fi/julkaisu/tutkimusraportti/tr_199.pdf