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 Hverahlíð for instance, started when boreholes were drilled in the area. Therefore, it may be inferred that these changes are due to utilisation of geothermal heat in the area.

Energy production at Nesjavellir and Hellisheidi/Hverahlid

In 2021, energy production at Nesjavellir and Hellisheidi was in accordance with the power plants' operating licence 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. However, it has been found that the production density is too high in some of the production fields, the pressure drop has increased in Hverahlíð and the negative effects of re-injection are within the Hellisheidi field.

Even though there are no plans for new power plants at the Hengill area, an extension of the current production area is anticipated, if full production capacity at Hellisheidi and Nesjavellir Geothermal Power Plants is to continue for the long term. Some preliminary research on the potential of future production areas have already commenced, to facilitate informed decisions on the future of power generation, and to guarantee sustainable utilisation of geothermal resources.

Reykjavik Energy Group places emphasis on sas ustainable utilisation of resources as possible, see video below (IS).

Discharge of geothermal fluids at Nesjavellir and Hellisheidi/Hverahlid

Geothermal fluid is reinjected into the geothermal system at Nesjavellit 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 sustainable utilisation.

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

At Nesjavellir, in 2021, approximately 75% of the geothermal fluid extracted from the geothermal reservoir was reinjected into the system, thereof approximately 10% into the geothermal reservoir. The development of the reinjection utility at the plant in recent years, has resulted in the discharge of geothermal fluid being at an all time low over the past three years.

Despite the great success of the reinjection system at the Nesjavellir Geothermal Power Plant, energy production is nevertheless accompanied by substantial discharge of heated groundwater at the surface. Groundwater has been extensively monitored in the past by recording boreholes and hot spring temperatures in real-time, and samples have also been collected since the power plant began its operations in 1990. The results do not show a decrease in groundwater temperatures, despite less discharge. The reasons behind these findings are not clear, but could be attributed to the following:

• The reinjection of geothermal fluid does not result in cooling of the groundwater because the reinjected fluid mixes with the groundwater, following flow paths underground in the bedrock.
• Improvements, made to the release routes, have not yet resulted in cooling of the groundwater in the lake Þingvallavatn.

At Hellisheiði, in 2021, approximately 75% of geothermal fluid extracted from the geothermal reservoir (separated water and condensate water) was reinjected. The condensate water (dense, pure steam) not used for reinjection evaporated in the cooling towers or was released in shallow reinjection wells. Some 1% of the geothermal fluid went into the overflow of the reinjection utility, due to either procedure or incidents in operations.

Increased supply of geothermal water to the capital area

The capital area was supplied with hot water from geothermal power plants for up to three months, during the summer of 2021. Going forward, 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 2021 was a considerable challenge in terms of surface dispercion at Nesjavellir due to unexpected failures and problems in maintenance projects at Veitur and ON Power.

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

Monitoring the ecosystem in the bay Þorsteinsvík, in the lake Þingvallavatn, 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

The reinjection of geothermal fluid can cause seismic activity, known as induced seismic activity, or triggered earthquakes, especially at the Húsmúli area. Blasting, associated with geological research and drilling in high-temperature fields, may also be the culprit. ON Power follows procedures, that are designed to minimise the risk of triggered earthquakes at and around the Hengill area.

In 2021 Reykjavik Energy Group did meet its objective to safeguard that seismic activity, potentially associated with the reinjection of geothermal fluid, would not cause an inconvenience and damage. An earthquake of magnitude 3.1 hit ON Power's reinjection area, despite the fact that no significant changes had been made to the reinjection. Therefore 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, due to changes in the process of reinjection in 2021.