Combining landslide and contaminant risk: a preliminary assessment

Abstract

Background, aim, and scope The aim of this paper is to highlight a not yet recognized hazard for mass failure (landslides) of contaminated soils into rivers and to provide an understanding of important interactions of such events. A first effort to investigate the problem is made focusing on the south eastern part of the Göta Älv river valley, in Sweden, by combining geographical information on potentially contaminated sites with slope stability levels on maps. The objectives of this study were to: (1) Review current Swedish risk assessment methodologies for contaminated areas and landslides, and analyze their capability to quantify the risk of contaminated areas being subject to landslides. (2) Investigate the presence of contaminated areas at landslide risk along the Göta Älv river valley. (3) Provide an overview of the national methods for landslide risk analysis and for environmental risk classification, followed by a comparison between the methods and the results from the superposition of the two methods for the study site. (4) Make a first attempt to conceptualize the release and transport mechanisms. Materials and methods Environmental risk assessment data of the study site was combined with data on slope stability levels. Conceptual issues of the release and transport scenario were identified and a first conceptual model was created. ResultsOf 31 potentially contaminated sites, eight had moderate to high probability for landslide, and of these eight sites, five were classified as having a high or very high environmental risk. These findings had not been revealed when the data had only been considered separately. The 'actual' risk could hence be even higher than the highest environmental risk class actually suggests. By visualizing results from the landslide risk analysis with the results from the environmental risk classification of contaminated sites, a better understanding of the potential hazard involved is obtained. Discussion The release mechanisms as a result of a landslide into surface water were conceptualized using two time scales: the instantaneous and the long-term release. It is clear that the Swedish method for landslide risk assessment and for environmental risk assessment of contaminated soil considers hazard events that are characterized by different time scales. The method for landslide risk assessment addresses events that are rapid (occurring over minutes) with instantaneous impact and consequences. Measurements are made within a short time after the event (days to months). The environmental risk assessment is done with respect to events that are slowly evolving (over years or decades) and any possible consequence materializes after a long period of time. Conclusions The combined data provided a more solid basis for decisions; however, inherent difficulties when combining data based on different methods were revealed. Separate assessment methodologies executed by different authorities may lead to incorrect assessments and inappropriate protective measures.Recommendations and perspective...

Sediments in urban river basins: a review of sediment–contaminant dynamics in an environmental system conditioned by human activities

“…2). For example, Göransson et al (2009) describe the present and historical importance of mass movement events in the urbanised Göta Älv river basin in Sweden. Given the propensity for most urban areas to be in the middle and lower parts of the river basin, the supply of sediment from non-urban land uses is from sources upstream of the urban area because of the downstream flow of water and sediment.…”

Mass transport of contaminated soil released into surface water by landslides (Göta River, SW Sweden)

“…Mouri et al (2011) modelled such a system by combining a slope model with a stream channel model. The study by Göransson et al (2009) divided the sediment transport from a landslide containing contaminated soil into an instantaneous release of sediment followed by a long-term release and presented a description of the processes involved (Fig. 1).…”

“…1. Schematic description of the release of contaminants into surface water from a landslide (further developed from Göransson et al, 2009). In landslide nomenclature, the zone where a mass movement is initiated is referred to as the "initiating zone", and the zone where deposition takes place is in general referred to as the "run-out zone".…”

“…The risk for the spreading of pollution from contaminated soil was only mentioned in a few of the landslides, but no measurements were ever carried out to analyse possible environmental consequences. There are several industrial areas adjacent to the river where a significant risk for landslides exists (Göransson et al, 2009). …”

“…If the water quality deviates from normal conditions, additional sampling will start automatically. However, as a direct consequence of the combined risk of landslide and contamination (see further Göransson et al, 2009), large investments are made on remediation and reinforcement of prioritised contaminated sites adjacent to the river.…”