Managing acid rock drainage through treatment and monitoring at E18 Motorway in Norway
The environmental challenge
Construction of the E18 Motorway required rock cutting and excavation through areas containing naturally occurring sulphide-bearing rock. When these minerals are exposed to air and water, they can react to form sulphuric acid. Rainwater and groundwater passing over or through the excavated rock can then become acidic and carry aluminium and other metals into nearby streams. This flow of water is known as acid rock drainage, or acidic runoff.
If it is not captured and treated, acidic, metal-bearing runoff can lower the pH of receiving waters, damage fish gills and affect fish survival and reproduction. It can also reduce populations of sensitive aquatic invertebrates, which are an important part of the aquatic food chain. Over time, this can reduce biodiversity and degrade the ecological condition of streams and other downstream habitats.
Following construction, Agder OPS Vegselskap AS was handed responsibility for managing this environmental legacy. This included operating three treatment plants and carrying out long-term environmental monitoring of the affected watercourses.
Since then, Agder OPS Vegselskap AS has worked systematically to treat the acidic runoff and assess whether water quality and aquatic ecosystems are recovering. Recent feedback from the Norwegian environmental authority, Statsforvalteren, has recognised positive and stable developments downstream of the treatment plants, including the natural re-establishment of fish and aquatic invertebrates at monitored locations.
The approach
Agder OPS Vegselskap AS operates three treatment plants that collect and treat acidic runoff before it reaches downstream watercourses. The treatment process is designed to reduce acidity and remove aluminium and other metals from the water before controlled discharge.
At the Stordalen treatment plant, chemical treatment is used to reduce concentrations of aluminium and other metals before the treated water is discharged into Stordalsbekken and subsequently flows into Kaldvellfjorden.
The treatment plants are supported by a long-term environmental monitoring programme. This assesses both water quality and the condition of aquatic ecosystems through:
- Water-chemistry analysis, including acidity, aluminium, sulphate and nitrogen compounds
- Surveys of fish populations
- Monitoring of aquatic invertebrates, which are sensitive to changes in water quality and provide an indicator of longer-term ecological conditions
- Comparison of results over time to identify improvement, deterioration or unexpected changes
The monitoring results are reviewed with environmental specialists and used to inform recommendations submitted to Statsforvalteren. This allows Agder OPS Vegselskap AS to adapt the monitoring programme and focus treatment and investigation on the locations where they remain necessary.
Outcomes
The long-term results show that water quality has improved and remained stable downstream of the three treatment plants.
Following recommendations submitted by Agder OPS Vegselskap AS over the previous two years, Statsforvalteren recognised the positive development and stability of the affected waters. Its feedback also acknowledged evidence of natural recovery, including the re-establishment of fish and aquatic invertebrates downstream of the treatment plants.
At locations where the desired water quality has been achieved and maintained, Agder OPS Vegselskap AS has recommended discontinuing selected monitoring activities. This reflects the consistency of the results collected over time. Monitoring will continue where further evidence or investigation is required, allowing resources to remain focused on the areas of greatest environmental need.
The results provide evidence that the treatment systems are contributing to improved conditions for aquatic life. However, ecological recovery is influenced by several factors and may take longer than improvements in water chemistry. The monitoring programme therefore considers both chemical and biological indicators rather than relying on individual water samples.
Key features
- Three treatment plants managing acidic runoff associated with sulphide-bearing rock excavated during construction
- Treatment designed to reduce acidity, aluminium and other metals before water is discharged
- Long-term monitoring of both water chemistry and aquatic ecology
- Positive and stable downstream developments recognised by Statsforvalteren
- Evidence of the natural re-establishment of fish and aquatic invertebrates
- Monitoring adapted according to environmental results and continuing needs
