Langøya hazardous waste landfill
NGI has worked as a consultant for NOAH over a long period of time, and has contributed to planning and designing, monitoring and following up activities at their landfill for hazardous waste, polluted soil and sediments at a former limestone quarry. The site has become a popular recreation area on safe ground.
Langøya hazardous waste landfill, the south quarry, before filling and restauration. ( NOAH)
The original limestone quarry on Langøya, an island outside Holmestrand in the Oslofjord south of Oslo, was designated as a suitable site for a hazardous waste landfill owing to the fact that the rock formation is impermeable throughout the area. The limestone quarry was driven down to a depth of 80 metres below sea level, and left open for several years. Sea water has not been registered to have penetrated the site.
Geotechnical and environmental consultant
Since the late 1980 's NGI has had many contracted assignments from NOAH at Langøya, with a geotechnical and geoenvironmental focus. NOAH's Langøya landfill has developed into a major and important ground-breaking project for NGI's geoenvironmental activities and has further strengthened our expertise in this area.
Over the years, NGI has provided geological mapping, sampling, testing and monitoring, which has been carried out in the laboratory and the field to assess land conditions with respect to density, stability and whether materials are fit for use as a barrier. In addition, NGI has been involved in geotechnical engineering solutions and landfill construction Methods.
NGI has also carried out work focusing on the properties of materials themselves that have been landfilled. Tests to determine permeability, chemical stability and leaching have all be carried out by NGI. NGI has provided advice and expertise to ensure that the landfilling activity at Langøya is operated in accordance with current standards and regulations. Relevant tasks include: environmental risk assessments, preparing applications for new concessions in accordance with regulations.
Solutions
Alternative solutions to improve barrier properties at the landfill have been given. Barriers must prevent the surrounding environment from any negative impacts. In some fracture zones lime-cement injections have been carried out to ensure this.
Stabilized hazardous waste in the liquid state has been deposited at the site below 0 m below sea level. Waste has been mixed with the liquid, which consists of a strong acid mixed with fly ash, forming a waste plaster. NGI has reviewed and recommended proper methods for stabilization of this mixture with respect to environmental and geotechnical stability. Mechanical stability has been assured by consolidation.
A monitoring system to verify that the landfill masses are safe and secure and result in minimal spreading to the surrounding environment was designed by NGI. The system included transducers to monitor pore water, ground water level, and deformation and settlements in the deposited masses, and also samplers that allowed measurements of air emissions.
The stabilized hazardous materials were deposited to 0 m below seas level at which point regular waste was disposed of up to the original terrain level at Langøya. The pore water, which dissipates out of the disposed materials above contour line zero, will be aggregated in a ring drainage system recommended by NGI.
The upper part of the top cap. The compacted clay crust which works as an impervious mineral layer can be seen on the right in the left image. Geotextiles (blue) will protect against evaporation, and to the left is seen the protection layer made of crushed limestone. The thickness of the limestone is governed by it to prevent frost penetration into the impervious layer. To the right NGI personnel carefully checks the impervious mineral clay layer. ( NGI)
Capping and transition to recreational area
A top cap was designed robustly using natural materials to seal the landfill site. A top crust dry clay was chosen as the capping material, acting as an impervious mineral layer. This cap will seal the underlying waste and ensure minimal water infiltration from rainfall.
A risk assessment of the sealed site shows that the cap works in accordance with the criteria set out in a permit from the Norwegian Authorities. The materials disposed of in the Langøya hazardous waste landfill site do not pose a risk of further contamination to ground water or the surrounding sea.
Nordbruddet (the north quarry) after completion, has been transformed into a recreational area. ( NGI)
The first part of the top cap in Nordbruddet (the north quarry) on Langøya was completed in early summer 2017. This was marked with an Open Day on the 26th August 2017, where representatives of, among others, the Holmestrand municipality, Central Government (Norwegian Ministry of the Environment), NOAH (owner), environmental protection organizations and NGI were present.
