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The Hazelwood coal mine in the Latrobe Valley, Victoria, Australia ceased operations in March 2017 with the closure of the adjoining Hazelwood Power Station. A water filled void with potential for recreational, agricultural, commercial and industrial uses is envisioned for the surrounding mine licence area following closure. A key step to achieving this is the capping of the coal ash ponds. At Hazelwood the coal ash ponds (approximately 100 hectares) are licenced as landfills and regulated by the Victorian Environment Protection Authority (EPA). The capping design is therefore required to be approved by the EPA based on waste categorisation as per landfill guidelines. In Victoria there are two dominant risk-based landfill capping types. For higher risk waste (categorised as ‘Category C’ waste) the EPA requires a composite lined cap consisting of a compacted clay (or geosynthetic clay liner (GCL) equivalent) and a high density polyethylene (HDPE) membrane. For lower risk wastes (categorised as ‘Industrial’ waste) the EPA permits a compacted clay (or equivalent GCL) only liner without a membrane. To enable EPA to make a risk-based decision, Environmental Resources Management Australia Pty Ltd (ERM) undertook detailed coal ash categorisation considering the Victorian EPA ‘Industrial Waste Resource Guidelines (IWRG) - Solid Industrial Waste Hazard Categorisation and Management’ (IWRG631) to satisfy the EPA that the coal ash was a lower risk and that a HDPE liner was not required. The IWRG631 guidelines provide upper total concentrations and leachability limits for waste categories (Category C and Industrial waste) to enable categorisation based on waste characterisation sampling results. The coal ash (waste) characterisation work included a desk top review of the consistency of the coal ash based on the coal type, power station operational history was undertaken by HRL Technology Group Pty Ltd (HRL) and ERM developed a detailed sampling program. Given the long history of deposition of coal ash deposition (50 years) and thus considerable volume of ash, it was not possible to meet the EPA’s volumetric sampling guideline. ERM therefore adopted an innovative statistical approach to determine a reasonable number of samples required to justify the coal ash categorisation. EPA agreed to the approach and ultimately determined a lower risk categorisation enabling the coal ash pond capping to be designed without a HDPE membrane and thus saving ENGIE Australia Pty Ltd (ENGIE) approximately $15 million in cap construction costs.

Coal ash waste categorisation to determine a regulatory capping profile for coal ash pond rehabilitation