Drilling started at Lake Onslow last week as geotechnical investigations of the feasibility of pumped-hydro storage got going.

Minister of Energy and Resources Megan Woods said drilling at Lake Onslow would provide “valuable insight” into the regional geology and its suitability in supporting pumped hydro infrastructure.

The geotechnical work would investigate rock strength, geological properties and features such as faults, landslips and shear zones, and the interactions between groundwater and surface water.

The first hole drilled would be about 100m deep and core samples would be taken and tested, with monitoring equipment installed to monitor groundwater flow over the long term.

“This work will help determine the best tunnel route and location for an underground powerhouse, and ultimately, give a better picture of the scheme’s technical feasibility and costs,” Dr Woods said. “These technical investigations will inform the broader Lake Onslow feasibility study that also considers the environmental, cultural, and social implications.”

At most sites, boreholes between 50m to 100m deep would be drilled with core samples extracted for analysis.

Test pits would be excavated to sample material near the surface and non-intrusive geophysical surveys also undertaken.

Geotechnical work would take place on private and public land. Owners would be asked about proposed work on their land.

Work at the first site was expected to be completed in early May. Additional work at other sites around the lake and Teviot Valley area would likely be completed throughout the year – resource consents and permissions allowing.

Sites would be examined by independent ecologists, archaeologists and cultural values assessors to ensure sensitive environments were avoided and impacts minimised.

Sites would be restored after drilling, and had been selected to lessen any disruption to the local community.

“I want to thank the local community and mana whenua for their willingness to work with us while we are in the information-gathering phase,” Dr Woods said.