Geothermal energy activity is monitored at the surface at the Hengill area. This area can be impacted by natural changes, as well as the production of geothermal energy. There is no definite way of discerning whether the changes occur naturally or from human action. The changes in surface activity at Hverahlíd field for instance, started when wells were drilled in the area. Therefore, it may be inferred that these changes are due to utilisation of geothermal heat in the area, please see map belove.

In the summer of 2023, it was noteworthy that significant geothermal activity surfaced, especially under Highway 1 in Hveradalabrekka near Hellisheidi geothermal power plant. ON Power closely monitors the situation in this area in cooperation with the Icelandic Road Administration.

Energy production at Nesjavellir and Hellisheidi/Hverahlid

In 2023, energy production at Nesjavellir and Hellisheidi was in accordance with the power plants' licences and ON Power's objectives. Maintaining the power plants' production capacity at the Hengill area has been one of the company’s most important tasks in recent years.

An extension of the current production area in Hengill is anticipated, to ensure sufficient supply of hot water in the capital area and full production capacity of hot water and electricity at Hellisheidi and Nesjavellir Geothermal Power Plants for the long term. Due to this, extensive work has begun in obtaining the required permits. This includes the expansion of the production field in Hverahlíd, an increased number of production and re-injection wells at Nesjavellir, and permits for exploratory drilling in new fields south of Hellisheiði.

The formal process of environmental impact assessment and planning for exploratory drilling in Meitlar and Hverahlíd II, as well as the planning process for the energy production field at Nesjavellir, began in 2023. Various field studies were conducted in the summer of 2023, such as assessments of geological features, vegetation, and bird life.

Reykjavik Energy emphasizes that the utilization of resources should be as responsible as possible and that biological diversity and ecosystems should be protected.

Discharge of geothermal fluids at Nesjavellir and Hellisheidi/Hverahlíd

Geothermal fluid is reinjected into the geothermal system at Nesjavellir and Hellisheidi Geothermal Power Plants, to protect surface and groundwater, as the geothermal fluid is warmer than groundwater and has a different chemical composition. The aim is also to increase the pressure in the geothermal reservoir, which in turn boosts responsible utilisation. There is full injection capacity for all separator water from both plants. In cases, where geothermal water is disposed of on the surface, the cause is unplanned interruptions in operation, which means that it is not possible to inject everything.

Various research and development projects have been conducted in recent years to fulfil reinjection requirements at Nesjavellir and Hellisheidi, with considerable success, please see appendix.

In 2023, over 76% of the geothermal fluid extracted from the geothermal reservoir at Nesjavellir was injected into injection wells, of which about 35% were injected back into the geothermal reservoir. Despite the success in the injection operations of Nesjavellir Power Plant, geothermal production is associated with significant discharge of heated groundwater to the surface, manifesting as thermal pollution in wells and springs near Lake Thingvallavatn. Efforts continue towards the development of injection deep into the reservoir, and injection into a new well began in the summer of 2023. This well received nearly 25% of all geothermal water from Nesjavellir Power Plant that was injected down in 2023, despite being in operation for just over half the year. The blending of geothermal water with district heating water for the Reykjavik Capital area is planned for 2026, with expectations that this will prevent the mixing of geothermal water into groundwater, see discussion on increased supply of geothermal water for the capital area below.

In June 2023, maintenance was performed on the Nesjavellir pipeline operated by Veitur Utilities. At the same time, ON Power undertook maintenance at the power plant's heating station. Extraction from the geothermal field at this time was at its peak due to electricity production, requiring the release of a lot of hot water to the surface and steam into the atmosphere. Concurrently, ON Power conducted maintenance on a machine at Hellisheidi Power Plant, which necessitated significant steam emission into the atmosphere. Unnecessary extraction of this valuable resource is wasteful, has negative environmental impacts and on reputation, and makes it more challenging to maintain the operation of the power plants for the future. ON Power and Veitur Utilities have been urged to better coordinate maintenance to minimize environmental impact and resource wastage.

Over 70% of the geothermal fluid (separated water and condensate water) extracted from the geothermal reservoir in 2023 at Hellisheidi was injected back into it. The condensate water (condensed pure steam) that was not injected evaporated in the cooling towers or was discharged through the overflow (around 1.5%). The overflow is used either to procedure or incidents in operations.

In 2023, it was a considerable challenge to keep surface discharges within the goals of ON Power due to maintenance projects and unexpected failures, but it was ultimately successful.

Increased supply of geothermal water to the capital area

In the summer of 2023, the entire Capital area received heated groundwater from the geothermal power plants in the Hengill area. Research into the integration of the capital region's heating supply system so that it is possible to mix geothermal water and heated groundwater from power plants is promising. The project will completely change the operating system of the heating supply and heat production in the geothermal power plants as the aim is to decrease production from low-temperature geothermal fields during the summertime, in order to further utilise the energy that is produced in power plants.

The year 2022 was a considerable challenge in terms of surface dispersion at Nesjavellir due to unexpected failures and problems in maintenance projects at Veitur Utilities and ON Power. Despite this, it was possible to keep surface dispersion within ON Power’s targets. Thus, there will be a significant reduction in the surface discharge of hot water at Nesjavellir, which will over time reduce thermal pollution along the shore of Lake Thingvallavatn.

Impact of discharge of geothermal fluids on the ecosystem in bay Thorsteinsvík

Monitoring the ecosystem in the bay Thorsteinsvík, in the Lake Thingvallavatn, began before the Nesjavellir Geothermal Power Plant was built. The results of measurements, made by the Natural History Museum of Kópavogur, show that trace elements from geothermal water, previously considered to have a negative impact on the ecosystem, do not show a statistically significant increase.

Analysis of the status of groundwater at Nesjavellir will continue, in order for ON Power to achieve its objective of reducing the environmental impact of the Nesjavellir Geothermal Power Plant..

Induced seismic activity

Injection of geothermal water, particularly in the Húsmúli field, as well as explosions associated with geological research and drilling in high-temperature fields, can cause induced seismic activity or micro-earthquakes. ON Power follows procedures aimed at minimizing the risk of triggered earthquakes in and around the Hengill area.

Reykjavík Energy's goal is to ensure that earthquakes potentially related to the injection of geothermal water cause minimal inconvenience and no damage, was met. In 2023, there was one earthquakes of magnitude 3 or over, in ON Power's injection fields. No changes were made in injection rates in 2023 and no notifications were sent to the Icelandic Meteorological Office's seismic activity division, or the Department of Civil Protection and Emergency Management of the Icelandic Police.