In 2010, HDL was successful in obtaining resource consents for the Stockton Plateau Hydro Scheme (SPHS). The consents create a 240GWh hydro resource by capturing all runoff from the Stockton Plateau. The plateau is the site of an operating open cast coal mine and multiple historic underground mines.
Acid mine drainage from these mines, a government liability, drains into the Ngakawau river. We can avoid this.
The Stockton Plateau Hydro Scheme is unique in that it creates a financially viable hydro resource while resolving an environmental liability created by 120 years of coal mining.
The Stockton Platea Hydro Scheme is designed to perform two complementary functions; 1) avoid contamination of Ngakawau River by collecting and diverting acid mine drainage from the coal mines on Stockton Plateau to an ocean outfall and 2) generate renewable electricity in the process. The consents for the scheme allow for both outcomes to be maximised within the physical constraints of the plateau. The scheme of works will be accessed using public and government roads, currently used and maintained by the miner. The scheme’s diversions and reservoirs are located downstream of the open cast and underground coal mines, ring fencing acid mine drainage.
The Stockton Plateau Hydro Scheme can be configured to address developers’ specific investment objectives within the environmental baselines established by the consents. The Ngakawau Restoration Project is an example of a configuration developed to address the specific requirements of Stockton Mine. The configuration balances capital costs against environmental outcomes. It will generate 140GWh from 24MW installed generation, offering hydro investment returns of up to 19%.
In 2018, the Treasury initiated a “Marked Sounding” to receive proposals for long-term solutions to rehabilitate acid mine drainage from Stockton Mine. HDL submitted the Ngakawau Restoration Project as the lowest cost long-term solution. The project will also serve the government’s policy objectives to increase renewable energy and support regional development, which will be a major issue at cessation of mining. Managing acid mine drainage liabilities should attract government contributions of up to 50% of the capital cost of building and operating the scheme. This is without valuing external social and environmental benefits, which are significant.
In July 2023, the Treasury, in partnership with BT Mining and local iwi, Ngati Waewae, provided a shortlist of possible acid mine drainage rehabilitation solutions to the Minister of Finance. The Treasury advised that the Minister’s assessment and subsequent processes are unlikely to be progressed until after the 2023 election and until there is greater clarity on when the miner is likely to quit the site. Mining licences expire in 2027.
HDL has proposed that a Special Purpose Vehicle (SPV) be established to implement the project. There are significant opportunities for the SPV if it is established prior to cessation of mining.
HDL invites expressions of interest in participation in the SPV