Tailings Dams
The inspection of mines and quarries tips and lagoons
The qualification requirements of the Competent Person
Mine and quarry tips and lagoons are principally covered under health and safety legislation by the Quarries Regulations, as well as by the EU Extractive Waste Directive through the Environment Agency guidance note EPR 6.14. The Quarries Regulations address in particular the “dry” slopes and tips prevalent on most UK mineral sites, for which the HSE has issued inspection rules and competence guidelines for engineers undertaking geotechnical assessments of excavations and stockpiles. HSE competence criteria generally define “competent in relation to a person as a person with sufficient training experience, knowledge and other qualities to enable them properly to undertake the duties assigned to them”. The Regulations require that everyone on, and those in the management structure of, a mineral site be competent and able to demonstrate this competence by the keeping of relevant records, including continuing professional development. The geotechnical competence defined in relation to the inspection of mines and quarries comprises a formal professional qualification, namely Chartered Engineer or Chartered Geologist status with three years’ relevant experience. Though compliance with these competence criteria is based on a less formal approach than that required under the Reservoirs Act, the system has in the main functioned satisfactorily for many years.
Mineral sites also include tailings dams and lagoons for the storage of water and silt, most of which are retained by embankment dams above the level of the surrounding land. These facilities include both active and inactive sites and range in volume from a few thousand to many millions of cubic metres, with confining embankments of up to more than fifty metres in height. All require regular inspection/appraisal/assessment by competent geotechnical engineers. Many of these retaining structures would be classified as “large raised reservoirs” were the sites not covered by mine and quarry legislation. This also applies to other non‑extractive industrial facilities under the remit of the Health and Safety at Work Act, such as ash and sewage lagoons. Further, a large number of these lagoons would be classified as high risk reservoirs due to their location or content. The inspection/assessment of such facilities therefore requires additional skills beyond those included in the HSE competence criteria outlined above. As will be appreciated, the impoundment of water/silt/tailings requires knowledge of dam design and construction and, for the majority of UK sites, general competence in hydrology. The additional engineering skills required, therefore, are those related to dam stability and flood assessments for which there is currently no equivalent formal competence requirement under the HSE. The published criteria are, by inference, restricted to geotechnical expertise, though the HSE has indicated that the level of competence should be commensurate with the risks associated with each facility. Therefore the HSE, though only providing guidance for geotechnical competence, expects inspecting engineers to have a relevant level of expertise and experience in other disciplines such as dam engineering, hydrology, geochemistry et al where the structure poses a significant risk. It is evident, therefore, that there is a gap in formal requirements for competence levels where mine, quarry or associated industrial sites include embankment dams retaining extractive wastes, process water or indeed fresh water. The converse is also true in that a reservoir engineer inspecting any mine, quarry or associated industrial facility would be expected to have relevant geotechnical skills in addition to those defined for a SE or an ARPE.
In 2008 a paper (Cambridge, 2008), reviewed and agreed before publication by Donald Lamont of the HSE, was presented on this subject to the Warwick Conference of the British Dam Society. In this paper the differences in application of the various Acts were presented, noting that the informal approach taken by the HSE in regard to competence had worked successfully for thirty years. However, implicit was the requirement to apply standards of equivalence on mine and quarry sites. These standards clearly require any quarry lagoon or similar impounding structure with a capacity of 10,000m3 to be designed to the same standard as the equivalent reservoir and for the risk assessments to be undertaken in a similar manner. However, underwriting the conclusions of this paper was the assumption that there would be an ongoing supply of engineers with feet in both camps, i.e. Competent Persons under Mines and Quarries Legislation and ARPEs under Reservoirs Legislation. This “supply chain” of engineers competent to oversee the UK stock of tailings, quarry silt and industrial lagoons is essential.
It should be clear from the above that the attributes of an ARPE most relevant to these tailings, quarry silt and industrial lagoons are those specifically related to embankment dam engineering and to flood hydrology. There is no formal training for a “Competent Person” as competence is based on both academic and professional qualifications as well as on experience in the field. A Competent Person for a tailings dam or large silt lagoon would be expected to have detailed geotechnical knowledge related to dams and foundations with subsidiary skills in hydrology, geochemistry et al as appropriate. It is evident that a SE or an ARPE with suitable levels of geotechnical skills would meet these competence criteria. It is incumbent on the HSE to ensure that all geotechnical engineers have relevant training and suitable experience to act as SQCE/Competent Person on UK mineral sites.
1. Defra, ‘How to comply with your environmental permit - additional guidance for mining waste operations’ EPR6.14, 2011
2. Cambridge M (2008) The application of the Mines and Quarries (Tips) and the Reservoirs Acts, Ensuring reservoir safety into the future, (Hewlett H. (ed.)), Thomas Telford Ltd, 2008
Mike Cambridge
Former ARPE
Cantab Consulting Ltd
Ashford
Kent TN24 8NU