In 2013, Stockton Mine proposed that HDL revise the configuration of the Stockton Plateau Hydro Scheme (SPHS) to focus on construction of the scheme's lower reservoir (Weka Reservoir), and to reduce capital cost, while meeting the mine’s consent requirements for managing acid mine drainage. The Mine proposed that parts of HDL’s scheme could be replaced with the parts of their own scheme, the Stockton Hydro Scheme (SHS), which provide for a penstock from Weka reservoir to a power station at Ngakawau, discharging treated water to the Ngakawau estuary. The SHS, with consents now held by the treasury, is unlikely to proceed as a stand alone scheme as its storage is within an ecological reserve.
HDL proposed 4 options to combine components of the SPHS and SHS.
Option 2 met the mines investment objectives. This configuration is referred to as the Ngakawau Restoration Project (NRP) to distinguish it from the consented Stockton Plateau Hydro Scheme. The configuration focuses on managing acid mine drainage liabilities from Stockon mine with 140GWh generated from 24MW installed generation at a power station located within the mine’s Ngakawau Coal Handling Facility. Smaller reservoirs will divert runoff from the plateau to an ocean outfall 75% of the time and from western catchments containing Stockton Mine 93% of the time, equivalent to the mine’s current consent obligations to meet conditions for treated discharge 90% of the time. The hydro investment would return up to 19% with appropriate contributions from the government for managing AMD on its behalf.
The configuration largely remains within the environmental baselines established by the consents for the Stockton Plateau Hydro Scheme and the Stockton Hydro Scheme. The licences and consents for ancillary works held by the mine would be available to the NRP. The NRP is described in NRP Concept Design Report and NRP Concept Design Planset.
In 2015, Hawkins Infrastructure (HIL) undertook due diligence and value engineering of the Ngakawau Restoration Project from the perspective of a potential constructor. Hawkins' assessment of the NRP was that the project was "viable, could be constructed as designed and that the costs were realistic". HIL lobbied the government which resulted in a presentation of the Ngakawau Restoration Project to Minister Steven Joyce as the lowest cost / lowest risk solution for the government's AMD liabilities. The Minister referred the unsolicited project proposal to the Treasury. HIL’s initiative ended in 2017 when the Hawkins Group was placed in receivership.
