Pollution level and reusability of the waste soil generated from demolition of a rural railway☆
Graphical abstract
Introduction
Every year, over 1,000,000 km of railroads carry billions of people and cargo around the world (UIC, 2012). In 2015, the US spent $ 64.9 billion on the operation, maintenance and modernization of this resource-efficient transport system (AAR, 2016). Likewise, South Korea plans to invest $ 48 billion on 5000 km of rail network by 2020 (KR Network, 2015). Railway projects (both large and small) generate a substantial volume of construction and demolition (C&D) waste such as sleepers, ballasts and sub-base soil, and can raise significant environmental concern. The three strategies in the waste management are to reduce, reuse and recycle before disposal (Yuan and Shen, 2011). However, authorities strictly limit reusing the C&D waste as they are often highly polluted (Korea Ministry of Environment, 2017; Government of South Australia, 2015).
Previous studies confirmed the accumulation of petroleum product, heavy metals and other hazardous material in railways (Vo et al., 2015). The typical detection of pollutants has conducted towards the negative perspective of railways as a threat to environmental safety. Furthermore, most of these investigations focused on functional parts, such as transport junctions, train depots and train stations which are regularly exposed to people, frights and maintenance works that make them prone to pollution (Wiłkomirski et al., 2011; Zhang et al., 2012). In contrast, rural railways, which are a major constituent of a rail network with a lower probability of pollution, are rarely evaluated for hazardous material. Overall, the conclusion made based on the partial observation from polluted areas may not accurately reflect the condition of railways in general. Furthermore, to the best of our knowledge, no studies have assessed the reusability of the C&D waste generated from a rural railway.
The sub-base soil of an abandoned railway has been reported alkaline with organic and inorganic matters, which supports plant growth (Wiłkomirski et al., 2011). Thus, the environmental and financial burden associated with the disposal of the railway waste soil may be reduced by reusing them for land reclamation or agriculture. Both biological and physicochemical treatments can remediate pollutants in the waste soil. Nevertheless, clean-up standards are difficult to meet using biological means within a typical construction schedule because of their slow treatment processes (Balba et al., 1998). Physicochemical methods can rapidly stabilize organic matters and immobilize heavy metals (Maroušek et al., 2015), but these methods are impractical for handling a large volume of the waste generated daily. Thus, reusing railway waste soil have had been impractical, however, it may be possible to reuse them without conditioning if the physicochemical characteristic and pollution level can ensure environmental safety.
This study evaluated the pollution level of the waste soil generated from the renovation site of an old railway in the rural area of Wonju, South Korea. The chemical properties, heavy metals, total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) were measured at different depths of the rural railway and compared with those of nearby agricultural land. Furthermore, the reusability of the waste soil as a soil amendment was tested through a lab-scale cultivation test using peas (Pisum sativum).
Section snippets
Collection of soil samples
Experimental samples were collected from three locations (Fig. 1) along the Seoul-Wonju Railway Route Renovation Project site in Wonju, South Korea (37°21′51.1″N 127°54′43.1″E). The old ballast structure consisted of three different layers of rock and sand (Fig. 1, Fig S1A). The top layer was 30 cm of track ballast (Ltop), the middle layer was 10 cm of sandy-loam (Lmid) and the bottom layer was sub-base soil (Lbot). The Ltop and Lmid showed signs of fouling (Fig. S1B), whereas the Lbot was
Organic content and hydraulic property of the railway waste soil
The waste soil sampled from the location 1, 2 and 3 had similar textures and chemical properties, but colors (Fig S2B) and LOIs (Table S1) were different among layers. The color of the Ltop and Lmid resembled Terra Preta (Fig. S2C), whereas the Lbot and CN matched sandy-loam. Likewise, LOIs of the Ltop (151.1 ± 13.0 g kg−1) and Lmid (143.3 ± 5.7 g kg−1) soil were significantly higher than that of the Lbot (43.2 ± 5.1 g kg−1) and CN (36.8 ± 5.0 g kg−1) soil. On the other hand, DOCs of the waste
Conclusions
The waste soil from railways is categorized as a hazardous waste generated by the accumulation of pollutants during the service life. However, the concentration of common railway pollutants in the rural railway assessed herein were considerably lower than that of other functional parts studied previously. The results from this study suggest that the waste soil generated from rural railways are much cleaner than perceived and proper application of the waste soil may enhance soil condition and
Acknowledgements
This study was supported by the Korea Ministry of Environment as “The GAIA Project” (2016000550005), the Korea Institute of Energy Technology Evaluation and Planning, and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20164030201250).
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This paper has been recommended for acceptance by Joerg Rinklebeis.