Ngāwhā shows that zero air emissions do not prove containment or whole-system environmental performance. Geothermal CCS must track carbon and fluid effects across connected receptors.
Ngāwhā is New Zealand’s first geothermal operation to reinject 100% of its non-condensable gases, predominantly CO₂. Its internationally rare record links reservoir behaviour with shallow groundwater and valued surface features through venting, partial reinjection and full reinjection. It provides a field case for testing whether zero reported atmospheric emissions demonstrate containment and whole-system environmental performance. The analysis combines predevelopment evidence and operational data since 1998 from reservoir, production, return fluid, tracer, spring, carbon balance, receiving environment and climate monitoring. Evidence points to development-related change through injectate returns reaching shallow receptors and indirect reservoir changes that propagate to groundwater and springs. Full reinjection is recent and its signal cannot yet be fully disentangled from increased production, changes in injection location and allocation, climatic drivers and natural variability. It may compound existing effects. Ngāwhā shows why precedent cannot be transferred uncritically to future geothermal carbon capture and storage projects. Impact assessment must track carbon and fluid redistribution across connected receptors from baseline through decommissioning and beyond. Transferability depends on system geology and chemistry, injection design, receptor connectivity and plant operation. Assessment limited to avoided air emissions and reduced Emissions Trading Scheme liability may overlook effects shifted to other receptors and their cultural and environmental values.
Mariana Zuquim is a University of Auckland PhD candidate and Waikato Regional Council geothermal scientist researching GHG reinjection and environmental performance in geothermal systems.