Closure planning for Collinsville Ash Dam

Specifications

• Client: Transfield Worley Power Services and RATCH Australia Corporation
• Scope:

  Risk assessment identified three main issues requiring detailed investigation to inform a closure plan: erosion stabilisation; leaching of contaminants to groundwater and heavy metal concentration in pasture grasses. By applying quantitative, mechanistic frameworks, Verterra quantified the risks, and identified the key design, management and monitoring measures required to achieve the over-riding closure objectives of a safe, stable, non-polluting, self-sustaining landform can be achieved. Manning’s Equation was applied to identify conditions that will lead to erosion, and inform design, management and monitoring criteria for a stable landform. A combination of observed concentrations and estimation of leaching potential was used to provide confidence forecast groundwater contaminant concentrations. Paired sampling and ANOVA was used to evaluate heavy metal concentration in pasture.

   
• Challenge:

  A practical, cost-effective approach to achieving regulatory agreement for progression toward full closure of a disused ash-dam was required to limit long-term liabilities and support other planned land-use for the site. This was believed to be the first application for regulatory approval of an ash dam closure in Queensland.

• Solution:

  Verterra undertook a risk-assessment approach to closure planning to limit the core issues that required investigation for development of appropriate management measures. Importantly, this was complemented by an adaptive approach of continuing remedial treatment as required, with closure criteria to be satisfied once monitoring parameters are stable and rectification requirements plateau. This provided a sound, evidence-based rationale for the clinet’s negotiation with the regulator, and ultimately, what is believed to be the first approval for an ash dam closure in Queensland.

• Benefit to Client:

  The approach delivered a sound, evidence and scientifically based closure plan to the client, supported by an informed integrated property management plan informed by quantitative studies, providing the client with confidence of establishing a path toward relinquishment and limitation of long-term liabilities.

• Market Sector: Power and Energy
• Capabilities:
  • Mine site, tailings dam and degraded land rehabilitation
• Location: Queensland
• Year: 2013 - 2014