Frequently Asked Questions

What is the anticipated generation capacity of the Project and will the power be injected into the local transmission network?
If Stockton Mine will be consuming some 32% (8MW) of the base load, what is their vested interest in this Project and are they planning to pay for it or a portion thereof?
The Project information states that construction of the hydro scheme has the potential to intercept 95% of the tributaries of the Ngakawau River affected by mining. What is meant by intercepting mine drainage?
Apart from the underground tunnels and workings at Granity, what are the other aspects of the Project described in the Project brochure as in areas of “low environmental value”?
Many people collect shell fish and use the Granity beach for recreational activities such as fishing. What is the effect of discharging sediment and heavy metals into the marine environment?
What is the involvement of Granity Stream in the proposal and what is meant by the “very small freshes” that are mentioned in the Project brochure?
The Granity tunnel passes through the MAPPS area, whereby there is an agreement in place with SENZ that the area will not be mined. What effect will construction of the Granity tunnel have?
There are several residents and businesses that receive their water supply from a header tank located near the Granity portal outlet. What effect will the Project have on this water supply?
What is the possibility of using rock excavated from the Granity tunnel and elsewhere within the Project footprint for coastal protection works?
To what extent will the Granity construction area be visible to residents and will noise cause disruption particularly at night time?

1. What is the anticipated generation capacity of the Project and will the power be injected into the local transmission network?

When fully commissioned the Project is expected to provide a continuous base load in the order of 25MW. It also has the potential to double the baseload output to around 50MW for short periods during and following heavy rainfall. (Note: For 2008 the West Coast's peak electricity demand is expected to be 75MW). The project ecomomics provide for upgrading the transmission network in 2017 if the capacity from the existing network has not been increased before then to transmit peak loads.

2. If Stockton Mine will be consuming some 32% (8MW) of the base load, what is their vested interest in this Project and are they planning to pay for it or a portion thereof?

The electricity generated from the scheme will be sold into the existing Buller Electricity network at market rates. Solid Energy currently buys electricity from the network. Having generation on site will improve security of supply to Solid Energy. HDL has yet to fund the scheme but there are no agreements in place with Solid Energy, other than sharing of environmental monitoring data and environmental studies relevant to the Project.

3. The Project information states that construction of the hydro scheme has the potential to intercept 95% of the tributaries of the Ngakawau River affected by mining. What is meant by intercepting mine drainage?

The Project not only generates electricity but has the added benefit of capturing in the scheme reservoirs, tributaries of the Ngakawau River degraded by mine drainage. There are a number of abandoned coal mines on the Stockton Plateau which are currently leaching acid mine drainage into tributaries of the Ngakawau River. These tributaries can be intercepted by the scheme reservoirs, in particular the orphan historic sites around Mt William and Fly Creek.

These sites can be regarded as contaminated sites, responsibility for which lies with the community and the crown. Grants can be sought from the crown, through the Ministry for the Environment to address management of these contaminated sites. For this to occur it requires the agreement of all the interested parities, such as landowners (Department of Conservation and Land Information New Zealand) and Solid Energy in terms of access. Note, Solid Energy only has responsibility to manage historic mine sites within their coal mining licence area.

4. Apart from the underground tunnels and workings at Granity, what are the other aspects of the Project described in the Project brochure as in areas of “low environmental value”?

Areas of "low environmental value" refers to the components of the hydro scheme on the Stockton Plateau, particularly the sites of the two reservoirs and the various stream intake structures, required to divert flows into the two reservoirs. The Project footprint is located in areas which have already been significantly modified by settlement and industry, particularly mining activity. Flora and fauna surveys have been undertaken on the Plateau, which determined that there is no significant loss of habitat or effects on species. All the intake structures for diversion of flows into the reservoirs are within waterways that have significantly degraded water quality and minimal fish life.

5. Many people collect shell fish and use the Granity beach for recreational activities such as fishing. What is the effect of discharging sediment and heavy metals into the marine environment?

The Project has the potential to capture 95% of the mine affected tributaries of the Ngakawau River. These waterways are currently affected by acid mine drainage and have elevated heavy metals and depressed pH's. The large reservoirs will provide dilution with rainwater, resulting in some improvement in water quality to these intercepted flows.

The principal components of the discharge into the marine environment is Iron and Aluminium. There are international guidelines (ANZECC) that provide thresholds for safe concentrations that have been used for the scheme design. On discharge into the marine environment the salt water causes precipitates to form which can cause a visible plume immediately around the outfall but which has no ecotoxic effect, due to the highly active nature of the seabed in the location of the outfall.

As regards the discharge of sediment, one of the critical design factors of the hydro scheme is that the turbines cannot tolerate abrasive material. In order to prevent sediment entering the turbines, sediment traps are to be incorporated at every intake point within the storage reservoirs, with sediment to be removed at regular intervals.

6. What is the involvement of Granity Stream in the proposal and what is meant by the “very small freshes” that are mentioned in the Project brochure?

Construction of the Granity tunnel will be undertaken from the Granity portal outlet. Some groundwater is expected to be encountered during the operation which will then require pumping out of the tunnel. This will be discharged into a settling pond situated adjacent to Granity creek, prior to final discharge into the same. The anticipated flows are likely to be minimal and will give no noticeable increase to the existing flows within Granity Stream.

The other potential discharge into Granity creek is through use of the emergency outflow pipeline. Discharge of tailwater from the Granity power station will be by means of a ocean outfall pipeline, with the discharge point some 600 metres offshore. Provision has been made for an emergency outflow pipeline discharging into Granity creek, this would only be used in the extreme circumstance that the main outfall pipeline became blocked or damaged in any way. Should this occur, there will be a time lag before flows through the Granity power station can be shut down up at the reservoirs and scheme diversions on the Plateau. It is expected that this may take up to 24 hours, hence the need for an emergency outlet.

This emergency discharge is what was referred to as being equivalent to the very small freshes which currently occur on a regular basis within Granity creek. These emergency discharges are not expected to have any effect on the Granity Stream channel but in the unlikely event that erosion occurred, this would be rectified by HDL.

7. The Granity tunnel passes through the MAPPS area, whereby there is an agreement in place with SENZ that the area will not be mined. What effect will construction of the Granity tunnel have?

The Granity tunnel will be deeply underground and will not be affected by any of the historic workings in the area. Drop shafts will be required along the tunnel route for ventilation and power feed, with these to be bored by a drill rig flown to the various sites. Ventilation shafts will be required along the tunnel route during constrcution. These will be constructed by boring up from the tunnel following a pilot drill holes bored from the surface by a rig flown into the various sites. Following construction, one shaft will be kept open to act as a pressure feilef valve (surge chamber). The others will be capped or will have intakes installed to collect acid mine drainage from the Miller and Granity Streams. However, the current consent application does not include any applications to take and divert Miller and Granity Streams and this could only occur if at some stage in the future additonal resource consents were obtained.

8. There are several residents and businesses that receive their water supply from a header tank located near the Granity portal outlet. What effect will the Project have on this water supply?

Construction activity at the Granity site may disturb this water supply. In the event that construction activity causes interruption to the surface or ground water flows that feed the header tank, HDL will arrange an alternative system. Any such alternative water supply will be monitored to ensure adequate water quality and quantity is available and will be established without any loss or interruption of supply to the present users.

9. What is the possibility of using rock excavated from the Granity tunnel and elsewhere within the Project footprint for coastal protection works?

Rock excavated from the Granity tunnel will be relatively small and not suitable for the exposed face of any rock wall but the formation of the Granity portal is likely to result in some large rock being excavated. Provided residents have the necessary resource consents in place HDL would be willing to transport rock for local coastal protection works.

10. To what extent will the Granity construction area be visible to residents and will noise cause disruption particularly at night time?

The access ramp up to the Granity portal outlet will be no wider than 6m and will be constructed to ensure that the vegetation below the road remains intact. The tunnel portal and apron will initially be obvious but over time is expected to be somewhat obscured by the surrounding dense vegetation. The construction yard will be largely contained in an area to the north of the Granity museum behind pine trees that border the railway line. A fence will be erected at the museum end of the yard with plantings along the fence frontage to provide a visual barrier. The construction phase for the project is expected to last no more than 5 years, at which time all plant and equipment will be removed form the site and the area landscaped in accordance with local residents wishes.

Although tunneling operations will occur 24/7 tunnel excavations during the night shift will be stored in a stone bay within the Granity tunnel so that truck movements occur only during the day shift. Once the Granity site is established heavy truck movements (just truck with no trailer) will be around 10 per day and should not be overly intrusive spread over a full work day.