Information for the community
Detailed information on the geotechnical investigations for the local community.
Key activities of geotechnical investigations
In the first half of 2022, resource consents were granted to undertake geotechnical, geological and hydrogeological investigations near Lake Onslow and the Teviot Valley area.
The key activities of this work were:
- drilling holes, about 15 cm wide and at various depths, from mobile drilling rigs
- excavating or digging test pits to sample the material at near-surface level
- monitoring groundwater and hydraulic testing
- non-intrusive surface geophysical surveys
- constructing a temporary storage area for contractors’ equipment and facilities.
Permission was also granted to take water from the Clutha River/Mata-Au and Teviot River/Te Awa Makarara, within permitted limits, to use in drilling operations.
Consents and other permits
Resource consents from the Central Otago District Council and Otago Regional Council were required to undertake this detailed geotechnical field work. Sometimes Wildlife Permits from the Department of Conservation were also required, depending on the nature of the field work.
Some consents came with conditions, such as erosion and sediment control measures, and work could not go ahead unless these conditions were met. Any proposal to drill or excavate on private land was discussed directly with the landowners before any consents were lodged.
Resource consent applications were granted for more investigation sites than needed to keep multiple options open until the optimal sites had been determined. This meant although a resource consent may have been granted, the work was not necessarily carried out.
Work at each site took approximately between 2 and 4 weeks – with times varying as each site presents different conditions.
Following completion of the work, the drill holes were covered and the area rehabilitated. The groundwater levels and pressure at some sites continue to be remotely monitored. At these sites, a small, fenced structure encloses the covered drill holes and a 5-metre pole with solar panels and data-logging equipment have been installed.
Geotech investigations across 3 areas
Work began in mid-April at the first location near Lake Onslow and was completed in September and only some remediation work at the site remains. The project team is working with the Central Otago District Council to remediate any road damage caused by the investigations.
Fieldwork in the Teviot Valley began in June. This fieldwork was located on public land, such as road reserves, at 2 main sites and was completed in September.
This work was investigating where on the Clutha River / Mata-Au water could be stored before being pumped through a tunnel to Lake Onslow. Depending on the location, this may involve constructing a lower reservoir. A lower reservoir would allow the pumped hydro scheme to take and return water and minimise any effects on the river.
The feasibility study has identified 3 possible areas for a lower reservoir – 1 at Lake Roxburgh where the lake would act as a reservoir, and at 2 sites further downstream. However more information is needed to help determine the most appropriate location, size and design for a lower reservoir, should the scheme go ahead. We are working directly with landowners who may be affected.
Further geotechnical work began at another site on private land in the Teviot Valley at the end of September as an extension of the fieldwork in the Teviot Valley. The main activities of this fieldwork concluded in October 2022. Some remediation work remains.
This location was selected for its near-surface-level geological features, and the information from this work will contribute to the broader design work of the proposed pumped hydro scheme.
All information from the geotechnical investigations will feed into the broader Lake Onslow feasibility study that considers the technical, environmental, cultural, social and commercial considerations of a pumped hydro scheme.
Throughout the geotechnical work programme, the NZ Battery Project team worked with field teams to ensure the work was done in a way that minimised disruption to the community. All work was carried out during the day and had minimal impact on traffic.
Sites for geotechnical investigation work were carefully selected through a Site Selection Protocol, with each potential location examined by an independent ecologist, archaeologist and cultural values assessor. The individual sites were selected based on this advice to avoid the impacts to sensitive environments such as wetlands, archaeological sites and where there is indigenous vegetation or potential lizard habitat. Where necessary, management plans were put in place to avoid or mitigate any adverse impacts.
The geotechnical work required physical investigations within the road reserve or on private land. The sites were located on pasture or existing modified areas wherever possible, to limit the potential effect on natural wetlands, wildlife and indigenous vegetation.
Advice and mitigation strategies from an independent ecologist were adopted to minimise any ecological effects. Some activities were conditional on obtaining a Wildlife Permit from the Department of Conservation.
All work on the site was subject to a Construction Environment Management Plan to ensure the works avoided or mitigated potential effects, as identified in the resource consent.
A Wildlife Permit from the Department of Conservation was obtained for investigations on sites where lizard habitats had been identified.
All sites were independently assessed for the potential effects the fieldwork would have on values to mana whenua. Recommendations from independent assessors were adopted into the planning to avoid or mitigate any potential adverse effects on mana whenua values.
The proximity of known archaeological sites was taken into consideration during the site selection process. If necessary, an archaeologist would attend the site to supervise and to provide advice in the event of a potential discovery. However, this has not been needed. Protocols for all sites were established in the event archaeological material was found.
Noise generated from the activity was broadly similar to the noise on a farm where machinery is operating.
The work had minimal impact on road users.
The sites in the first stage of fieldwork were dispersed across a large area and scheduled for different times, which minimised the number of extra vehicles on the roads or parked on road reserves. There were up to 3 vehicles and a mobile drill rig at each site, as well as occasional visitors.
The second stage of fieldwork in the Teviot Valley followed similar procedures. A traffic management plan was implemented where works were required within the road reserve. This was to ensure the continued safe and efficient operation of the road network.
Sites where the ground has been disturbed are being remediated to leave little to no evidence of activity.
However, at some sites, a small area around the covered drillhole is fenced off and a small solar panel, monitoring equipment and telecommunications equipment has been installed so groundwater data can be collected and monitored remotely.
Social and cultural impacts
We recognise the fieldwork may have heightened uncertainty for some in the community. We remain committed to keeping the community informed about the project, especially affected landowners and mana whenua.
As part of our feasibility study, we have commissioned work to research the likely impacts the proposed scheme would have on the community and mana whenua.
The social and cultural impacts will be included in the Lake Onslow feasibility study that will be presented to Cabinet Ministers in December 2022, along with the technical, environmental and commercial considerations.
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