DSpace at VNU: Stormwater quality management in rail transportation - Past, present and future

DSpace at VNU: Stormwater quality management in rail transportation - Past, present and future tài liệu, giáo án, bài gi...

Science of the Total Environment 512–513 (2015) 353–363 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Review Stormwater quality management in rail transportation — Past, present and future Phuong Tram Vo a, Huu Hao Ngo a,⁎, Wenshan Guo a, John L Zhou a, Andrzej Listowski b, Bin Du c, Qin Wei d, Xuan Thanh Bui e,f a Centre for Technology in Water and Wastewater, School of Civil and Environmental Engineering, University of Technology Sydney, Sydney, NSW 2007, Australia Sydney Olympic Park Authority, Figtree Drive, Sydney, NSW 2127, Australia School of Resources and Environmental Sciences, University of Jinan, Jinan 250022, PR China d Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, PR China e Faculty of Environment, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam f Division of Environmental Engineering and Management, Ton Duc Thang University, District 7, Ho Chi Minh City, Viet Nam b c H I G H L I G H T S • • • • Stormwater management in the railway industry focused solely on drainage Stringent stormwater quality standards require urgent responses from the industry Railway transportation generates potential sources of pollutants for runoff Urban retrofitting provides opportunities for railway stormwater management a r t i c l e i n f o Article history: Received 29 December 2014 Received in revised form 23 January 2015 Accepted 23 January 2015 Available online 29 January 2015 Editor: D Barcelo Keywords: Stormwater quality Railway industry Stormwater treatment Urban retrofit a b s t r a c t Railways currently play an important role in sustainable transportation systems, owing to their substantial carrying capacity, environmental friendliness and land-saving advantages Although total pollutant emissions from railway systems are far less than that of automobile vehicles, the pollution from railway operations should not be underestimated To date, both scientific and practical papers dealing with stormwater management for rail tracks have solely focused on its drainage function Unlike roadway transport, the potential of stormwater pollution from railway operations is currently mishandled There have been very few studies into the impact of its operations on water quality Hence, upon the realisation on the significance of nonpoint source pollution, stormwater management priorities should have been re-evaluated This paper provides an examination of past and current practices of stormwater management in the railway industry, potential sources of stormwater pollution, obstacles faced in stormwater management and concludes with strategies for future management directions © 2015 Elsevier B.V All rights reserved Contents Introduction Conventional approach to stormwater management in the railway industry Stormwater quality management practices in the railway industry 3.1 Rationale 3.1.1 Recognition of non-point source pollution from the transportation sector 3.1.2 Contamination along railway tracks and stabling yards 3.2 Potential sources of stormwater pollution in the railway industry 3.2.1 Wooden sleepers 354 354 355 355 355 355 355 355 ⁎ Corresponding author at: School of Civil and Environmental Engineering, University of Technology, Sydney (UTS), P.O Box 123, Broadway, NSW 2007, Australia E-mail addresses: ngohuuhao121@gmail.com, h.ngo@uts.edu.au (H.H Ngo) http://dx.doi.org/10.1016/j.scitotenv.2015.01.072 0048-9697/© 2015 Elsevier B.V All rights reserved 354 P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 3.2.2 Herbicides and pesticides 3.2.3 Fuels, oils and lubricants 3.2.4 Wear and tear 3.2.5 Embankments 3.2.6 Human waste and littering 3.2.7 Maintenance facilities 3.3 Pollution routes 3.4 Challenges in stormwater quality management in the railway industry 3.4.1 Input data 3.4.2 Monitoring and modelling 3.4.3 Treatment challenges 3.4.4 Regulations, policies and standards Provisions for stormwater quality management in the railway industry 4.1 Source control 4.2 Stormwater treatment and harvesting 4.2.1 Stormwater treatment 4.2.2 Stormwater harvesting 4.3 Urban retrofit Conclusion Acknowledgements References Introduction Among the many endeavours of society to promote a sustainable transportation system, railway networks play a crucial part because of their substantial carrying capacity A rough statistic from the World Bank (2014) showed that the combined length of the world's railway lines increased dramatically by 40% from 1990 to 2012 Compared to roadway transport, railway is considered more environmentally friendly in providing mass transporting services with less negative ecological impact (Zimmerman, 2005) Nonetheless, the environmental benefits from railway transportation over private vehicles are undeniable Hence, railway networks are likely to be upgraded in order to meet greater transportation and environmental demands (Kamga and Yazici, 2014; Zhiqun and Jiguang, 2011) Although emissions from railway systems are far less than that of automobile vehicles, the environmental pollution from railway operations should not be underestimated Frequently mentioned types of impact caused by rail transportation include noise (Aasvang et al., 2007; Ali, 2005; Trombetta Zannin and Bunn, 2014), vibration (Kouroussis et al., 2014; Sanayei et al., 2013) and air pollution (Dincer and Elbir, 2007; Salma et al., 2009) In contrast, there have been very few studies into the impact on water courses This lack of interest does not imply that water pollution from the railway industry is an insignificant issue As Osborne and Montague (2005) stated, “railway operations, both current and in the past, have the potential to give rise to pollution, as water drains from the railway into water courses” Yet, to date, priorities in water management for rail tracks still solely focus on its drainage function Hence, upon realising the significance of nonpoint source pollution, stormwater management priorities should have been reevaluated This paper will provide an examination of past and current practices of stormwater management in the railway industry, potential sources of stormwater pollution, management obstacles and future directions Conventional approach to stormwater management in the railway industry Rail tracks and supporting systems attracted the most attention in stormwater management plans for the railway industry as they were the backbone of railway services This heightened attention was due to the negative impact of runoff on rail tracks directly threatening rail safety 356 356 356 358 358 358 358 359 359 359 359 360 360 360 360 360 361 361 362 362 362 Based on the track support systems (or substructures), rail tracks are divided into three categories: traditionally ballasted, modified ballasted and ballastless Configurations of these substructures were well presented in the works of Esveld (1997) and Teixeira et al (2009) While the latter types of rail tracks developed due to demands for highspeed trains and low maintenance frequency, ballasted railway tracks have still been employed extensively, thanks to their enormous economic advantages A typical ballasted substructure comprises of a top ballast layer (150–550 mm of single-sized rocks), a sub-ballast layer (90–450 mm of well-graded crushed rock or a sandy gravel mixture) and an underlying subgrade layer (natural or amended soil) Each layer performs different structural functions to ensure the durability and stability of a rail track Precipitation falling on ballast quickly drains to the sub-ballast layer and then runs into drainage systems The drainage system could be either a parallel pipework network or a natural ditch, which is located along the sides of the embankment toe Similar mechanisms were found in depots or maintenance centres The influence of runoff from surrounding areas on the rail track areas is often restricted to ensure the safety of the track bed The effect of runoff volume on rail tracks was investigated thoroughly, as the saturation of water in these layers can reduce the stiffness of the track foundation (Australian Rail Track Corporation Ltd., 2006) The flow hydraulic properties vary depending on the type and age of the track bed Drainage capacity of a track decreases over time, as sediments accumulate in its body (Burkhardt et al., 2005) Rushton and Ghataora (2014) observed that greater impact occurred when water accumulated in the sub-ballast and subgrade layers, where finer grains were predominant Under the load of moving trains, trapped water became pressurised, drawing clay or silt from the subgrade upward to the ballast layer, known as the “clay pumping” phenomenon (Rushton and Ghataora, 2009) Together with the depositing of dust and abrasive materials on the ballast surface, clay pumping can cause ballast fouling (Indraratna et al., 2011) The fouled ballast further degraded the drainage capacity of the track support system and led to structural deformation Due to its high risk of rail track structural deformation, stormwater was a critical problem for rail operation Stormwater runoff had subsequently been perceived as a nuisance that must be drained as quickly as possible For modified ballasted systems (with a bituminous or geotextile layer working as the sub-ballast layer) and ballastless systems, the effects of stormwater on the foundation structure are less severe EAPA (2003) pointed out three main reasons for this improvement Firstly, an asphalt layer distributed train loadings more uniformly, hence P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 eliminated the “clay pumping” phenomenon in the upper ballast layer Secondly, a dense layer of asphalt moved water away quickly to protect the top layer Finally, the impermeable bituminous layer can act as a barrier to block the upward movements of silt materials from the subgrade (or foundation) layer Due to drainage being the focus of stormwater management systems, only hydraulic profiles were considered in design Collected stormwater from the drainage systems were then discharged into natural water bodies, including rivers, streams, creeks or even drinking water catchments, while its effects on the basin were completely ignored No quality consideration was found in any official technical guidance for drainage systems in the railway industry (Australian Rail Track Corporation Ltd., 2013; U.S Army Corps of Engineers, 2004) Stormwater quality management practices in the railway industry 3.1 Rationale The above perception remained unchanged until recent years when stormwater management objectives were re-assessed due to the following reasons 3.1.1 Recognition of non-point source pollution from the transportation sector An abundant number of papers have highlighted the existence of pollution from diffuse sources over the last 40 years (Clark and Pitt, 2012) When most effluent discharges were moderately controlled, stormwater then became one of the largest non-point pollution sources contributing to the degradation of surface water resources (National Research Council, 2008) Unlike effluent discharges with relatively stable characteristics, there is wide variation in stormwater quality and quantity Attempts to build roadway runoff profiles were accomplished universally While an insignificant concentration of biological oxygen demand (BOD5), bacteria and nutrients are found in stormwater, it is a substantial source of heavy metals and polycyclic aromatic hydrocarbons (PAHs) (Barbosa et al., 2012) These constituents were often accompanied with finer particles (Barbosa et al., 2012; Kayhanian et al., 2012) To reduce the negative impacts of runoff, several countries set up regulations for stormwater pollution control, such as the National Pollutant Discharge Elimination System Stormwater Program (1990) in the US and the “Water Framework Directive” (2000) in the European Union A few states in the US even issued more stringent industrial stormwater permits As a result, the railway industry must comply with these new requirements An understanding of stormwater quality from railway operations is a prerequisite for applying effective pollution-reduction measures required to fulfil these tightening regulations (Kayhanian et al., 2012) Despite the practical needs to understand stormwater quality profiles, available literature has shown little information pertaining to this issue It imposed a large burden on the old rigid engineering systems of the railway industry As Dunning and Weiner (2011) argued, stormwater management turns out to be one of the largest struggles that the railway industry has to overcome in the coming years 3.1.2 Contamination along railway tracks and stabling yards Railway is an important means of freight transport over long distance at reasonable cost It is the preferred choice for transporting crude oil This, consequently, has caused the environmental risks associated with rail to increase As evidence of this, more than 4350 m3 of oil was released into the environment due to rail incidents in America in 2013, which was equal to 150% of past four decades put together (Tate, 2014) Although clean-up activities could reduce the harmful effects to some extent, the accumulated oil in the soil could pollute stormwater in much later years, as in the case of Osborn Yard in Louisville, Kentucky (Kurzanski et al., 2013) Signs of oil pollution appeared in 355 the stormwater run-off as a result of diesel spillage incidents that occurred 20 years ago Apart from incident-related causes, daily railway operations were also proven to affect the soil quality along rail tracks and supporting infrastructures Malawska and Wiłkomirski (2001) surveyed concentrations of nine metals (Co, Cd, Cr, Cu, Fe, Hg, Mo, Pb, Zn) and 14 priority PAHs in soil samples taken from four railway locations – the siding, the main track within the platform, the cleaning bay and the loading ramp – at the Iława Głowna junction (Poland) Most of the substances tested for, except Mo, were at substantially higher concentrations than in the control sample The largest concentrations of pollutants were found near the platform and railway siding areas where trains spent long periods of time at low speeds Metals detected at high concentration were Fe (10,800–50,600 mg/kg dry weight), Zn (84–1244 mg/kg dry weight), Pb (55–506 mg/kg dry weight) and Cu (24–115 mg/kg dry weight) 13 years later, the authors executed comparative research at the same locations PAHs had significantly increased by 8–25 times, which turned the soil from “slightly polluted” class to “polluted” and “heavily polluted” classes, with reference to Polish and Dutch regulations (Wilkemirski et al., 2011) To a lesser extent, metal levels had also magnified by 1.2 to times The investigation of heavy metals along rail tracks in Qinghai–Tibet railway (Zn, Cd and Pb) and Suining railway station (Pb and Cd) provided similar results (Chen et al., 2014; Zhang et al., 2012) Even though the movement of these pollutants from soil to water environment has not been studied in great detail, soil pollution in rail track areas could potentially result in stormwater contamination (Burkhardt et al., 2008) 3.2 Potential sources of stormwater pollution in the railway industry Emission sources from the railway industry can be divided into two groups — those associated with daily operation (i.e affected by the frequency of trains) and those independent of rail traffic volume (i.e supporting infrastructures) The main sources of pollutants from daily operation include: (1) wooden sleepers, (2) herbicides for vegetation control, (3) fuelling and lubrication, (4) wear-and-tear processes and corrosion-resistant poles, (5) embankment materials and (6) human activities The pollution from incidents such as oil spillage that were briefly presented in the previous section is not the focus of this paper 3.2.1 Wooden sleepers The most significant source of organic compounds in railway runoff comes from creosote-impregnated wooden sleepers Creosote is a fusion mixture of more than 162 compounds including PAHs (69%), nitrogen heterocyclics (11%) and other aliphatic hydrocarbon (Utley, 2005) It has been used as a fungicide to enhance the lifespan of wooden sleepers (Brooks, 2001) Although the toxicity of creosote is low (Chakraborty, 2001), it is identified as a potential carcinogen due to its PAH components In Switzerland, creosote-loaded sleepers accounted for 43% of annual stock (Kohler et al., 2000) Nevertheless, the country with the highest demand for wooden sleepers is the US For instance, the US required approximately 17 million new sleepers in the year 2008, 91% of which were wooden (AREMA, 2008) The main reasons for the popularity of wooden sleepers come from their impressive ability in the dynamic attenuation of loadings, their light weight, their ease to install and maintain, and most importantly, their economic viability The average loss rate of creosote in rail sleepers was about 210 mg/m2·day for 20–30 years in service, of which PAHs accounted for 20 mg/m2·day (Kohler et al., 2000) Despite this, the asserted possibility of creosote leakage into water was considered debatable Brooks (2004), in his 18-month study to investigate the seepage of creosote from railway sleepers to adjacent environments, suggested that leakage of creosote via stormwater was negligible The authors argued that creosote loss was accompanied mostly with vaporisation, weathering and deposition in railway ballast Thierfelder and Sandström (2008) also 356 P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 stated that creosote-impregnated wooden sleepers used for embankments would expose no risk to the water environment, albeit no evidence was given for this conclusion On the other hand, Kang et al (2005) explored the migration of 16 priority PAHs from impregnated wooden sleepers in fresh water under different flow-rate regimes in one week Seven lower molecular weight PAHs (acenaphthene, anthracene, naphthalene, fluoranthene, fluorene, phenanthrene and pyrene) were detected in the leakage water in all cases Chakraborty (2001) also studied three different mechanisms of creosote loss – bleeding, leaching and vaporisation – for eight light PAHs (the previously mentioned PAHs and acenaphthylene) It was found that the main mechanism for PAHs loss was leaching (more than 50%), rather than vaporisation and bleeding In addition, Becker et al (2001) explored the leaching behaviour of creosote in treated wood in three media — deionised water, buffered solution at pH 4.7 and humic mixture liquid In their research, nitrogen heterocyclics and several PAH compounds were leachable in all media Heterocyclic nitrogen substances (quinoline, isoquinoline, indole and 2-methyl-quinoline) were leaked with a higher rate than that of PAHs The highest leaching rate was quinoline with 1050 mg/kg of wood after 24 h of submerging in water The leaching rate for PAHs such as naphthalene, dibenzofurane, phenanthrene and pyrene was much lower, only 2–38 mg/kg of wood The leachable quantities of PAHs were minor compared to its extractable quantities (0.1–3.0%) by using Soxhlet extraction method with toluene solvent It could be concluded that heavier PAHs tend to attach to organic matters and sediments whereas lighter PAHs are able to dissolve with a low concentration into stormwater, normally much lower than its solubility (Table 1) 3.2.2 Herbicides and pesticides Weed-growth on roadbeds or embankments is strictly controlled as they may (1) impede a driver's ability to see signals, (2) impede staff members working in rainy weather, (3) impede inspectors examining track damage or (4) become fire hazards (Victorian Rail Industry Environmental Forum, 2007) Although different methods of weed control have been considered, chemical herbicide spraying appears to be the most economically feasible (Torstensson et al., 2005) Table summarises several toxicological parameters of typical herbicides applied in the railway industry Among these herbicides, diuron has been prohibited since the late 1990s in the railway industry because it is toxic and highly mobile Its strong mobility resulted in the destruction of a vast majority of pine trees along the rail corridors in Sweden (Torstensson et al., 2002) Table Leaching rates for priority PAHs from impregnated wood in different types of water Experiment conditions Kang et al (2005) +Medium +Temperature +Time Fresh water Deionised water 12–13 °C – days 120 h Substance Unit Naphthalene Acenaphthene Fluorene Phenanthrene Fluoranthene Pyrene Quinoline Isoquinoline Indole 2-Methyl-quinoline Dibenzofuran Becker et al (2001) Buffer solution – 120 h Humic solution – 120 h μg/cm2·day mg/kg wood mg/kg wood mg/kg wood N/A N/A N/A 0.2–0.5 N/A N/A – – – – – 108 ± 14 37 ± 30 ± 44 ± 6±2 4±2 1890 ± 180 205 ± 21 374 ± 33 150 ± 57 ± 105 ± 31 31 ± 31 ± 60 ± 27 27 ± 19 21 ± 16 1760 ± 170 354 ± 35 544 ± 66 254 ± 26 41 ± 77 ± 12 49 ± 42 ± 10 44 ± 22 ± 14 ± 2450 ± 180 427 ± 18 706 ± 23 354 ± 38 46 ± Nevertheless, diuron has still been used for weed control in numerous countries due to its long-lasting effectiveness Glyphosate then emerged as a safer alternative Compared to other herbicides, glyphosate has higher water solubility but lower toxicity (Schweinsberg et al., 1999) In an investigation of pesticide application in the UK, Croll (1991) discovered a disproportionate amount of triazine concentration in surface water compare to the amount utilised in agriculture Croll suspected that a substantial part of this type of pesticide originated from weed control for railway and roadway A similar observation was made by Skark et al (2004) Indeed, the average application rate of herbicides per area for railroads was claimed to be six times higher than that being applied in agriculture (Schweinsberg et al., 1999) Some papers discovered the existence of herbicides in surface water in railway territories The concentration of herbicides exceeded the drinking standard of 0.1 μg/L in the surface water near the railway lines (Cooker, 1996; Schweinsberg et al., 1999) They accumulated in the drainage ditch of a disused railway section at levels as high as 800 μg/L (Heather and Hollis, 1999) Besides these contaminants, the arsenic level in soil along abandoned rail tracks in South Australia was measured to be within the range of 17–1000 mg/kg, exceeding acceptable limits (5–40 mg/kg) (Smith et al., 2006) as a consequence of the use of As-based herbicides 3.2.3 Fuels, oils and lubricants Leakages of petroleum products from fuel storage tanks, filling stations, locomotives and transformers are also frequent sources of water pollution Risks from oil leaks are directly proportional to the share of diesel locomotives in the railway industry The conversion from diesel-powered trains to electric trains in railway networks is underway worldwide, but has encountered various unfavourable hurdles More than two-thirds of locomotives in the railway industry are currently powered by diesel (World Bank, 2007) The fraction of diesel locomotives is extremely high in regions where freight transportation over long haulage distances is predominant, for instance North America (99%), Latin America (97%) and Australia (95%) (World Bank, 2007) This is because freight trains only need simple infrastructure and low levels of electrification spanning over long sections In contrast, passenger trains require higher levels of electrification because they run through and connect multiple high-density metropolitan areas Thus, currently, railway electrification efforts are chiefly accelerated in populated metropolitan regions or in ambitiously developing countries such as India and China (Juhasz et al., 2013) Furthermore, oil and grease are also commonly used for lubricating curves, gears and engines Despite this, information relating to oil leakage in railway operation is incredibly scarce Only one Swedish survey exists on this topic, presenting the oil leakage rates of various transformers The rates for large transformers, booster transformers and auxiliary transformers are 10, and 0.5 L/year, respectively (Gustafsson et al., 2007) In a recent study on the stormwater runoff profile from railway bridges, Gil and Im (2014) found the concentrations of oil and grease in a concrete road-bed and a gravel road-bed were 0.20–2.90 and 0.61–6.70 mg/L Oil leakages contain a high concentration of carcinogenic PAHs Some organic compounds, even in small amounts, can cause odour and aesthetic problems Highly mobile hydrocarbon components pose higher risks to the receiving water bodies 3.2.4 Wear and tear The largest source of heavy metal emissions originated from friction processes — rolling stock braking (73%), rail (21%), wheel (5%) and then power line (1%) (Burkhardt et al., 2008) Both embankments and surrounding areas of the railroad were contaminated with metals (Bukowiecki et al., 2007; Gustafsson et al., 2007) Iron accounted for the highest portion of metal emission in the braking and abrasion processes, followed by Mn, Cr and trace amounts of Ni, Mo, V and Pb Meanwhile, power line abrasion contributed the biggest quantity of Cu while Zn was emitted from galvanised poles at a quantity of 140 g/pole/year P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 357 Table Representative herbicides used in railway industry Herbicide unit LD50a (g/kg) Phenoxy-carboxylic acids 2,4-D 0.4 2,4,5-T MCPA 0.5 0.7 Dichlorprop 0.8 Triazines Atrazine 2.0 Hexazinone Simazine Terbuthylazine Propazine 1.7 N5.0 2.0 ADI (mg/kg) RfD (mg/kg per day) LC50 (mg/L) DT50 Notes 0.3a 0.01f 0.03a 0.00015a 0.01f 0.03f 0.01a 100e b7 dayse – 0.01a 0.0005a 0.0044g – 0.54–0.77h 232e – 1–10 dayse – – 521e 21–25 dayse – 0.0007a 0.005f 0.1f 0.005a 0.003f 0.02f 0.035a 176h 19–120 daysk Germany: used until 1991a 0.035a 0.005a 0.02a – 5h (rat) – 2.04m 8–92 days k 27–216 days i 10–36 daysk 131 daysm Germany: used until 1989a – – – Urea derivatives Bromacil Chlorotoluron Diuron 5.2 N10.0 3.4 0.1f 0.0005a 0.00003a 0.007f 0.1g 0.002a 0.002g – – – 12–46 daysk – 12–48 monthsd Isoproturon Monuron 1.8 3.7 – – – – – – 14–29.5 daysj – Germany: using from 1989a – Germany: used until 1996a Holland: used until 1999 Sweden: used between 1974 and 1993b UK: used until 2008 – – Miscellaneous Amitrole Dalapon Picloram Imazapyr Glyphosate N5.0 3.9 3.8 – 4.5 0.001l – 0.07f 2.5f 0.3a 1.13g – 0.2g – 0.1a 0.439 (rat)l – 26e N100e 86e 50 daysl – 30–90 days e 2–6 months d 2–5 months d 3–174 days e Germany: used until 1989a Germany: used until 1990a Germany: used until 1989a EU: used until 2004e Germany: using since 1987a Sweden: using since 1986c Notes: ADI: acceptable daily intake LD50: lethal dose for rat (oral) RfD: reference dose for chronic oral exposure LC50: lethal concentration for fish DT50: disappearance time for 50% of substance a Adapted from Schweinsberg et al (1999) b Adapted from Torstensson et al (2005) c Adapted from Gustafsson et al (2007) d Adapted from Torstensson et al (2005) e Adapted from Britt et al (2003) f Adapted from Bending and Rodriguez-Cruz (2007) g Adapted from Department of Health — Office of Chemical Safety (2014) h Adapted from Dikshith and Diwan (2003) k Adapted from Directorate-general health and consumer protection (2001) i Adapted from Gunasekara et al (2007) j Adapted from Hayes and Kruger (2014) l Adapted from Sarmah et al (2009) m Adapted from University of Hertfordshire (2013) due to data for the former group being both lacking and inadequate Thus, Table was given as a rough guide to locate the ratio of railway runoff contaminants within the general railway runoff profile and benchmark values The benchmark values for stormwater pollutants proposed by the US Environmental Protection Agency (2009b) were used to represent the “level of concern” to receiving water quality (Burkhardt et al., 2008) Most metals were bound with particles while some were released in the dissolved phase (Zn, Cu and Ni) The distribution of metals depends on spatial and temporal scales which have not been studied Three studies reported the existence of metals in railway runoff (Gil and Im, 2014; Gill, 2012; Larsson, 2004) Apparently, it is difficult to compare between railway runoff and highway runoff quality Table Metal concentrations in runoff from highway and railway Component (μg/L) Zn Cu Cd Pb Cr Fe Source of data Railway Railway bridge Station Stabling yard Highway Benchmark value – 950 23–180 63–1784 117 25–270 46.3 25–92 5.5–11.7 63.6 0.015–3.1 1.3 b0.1 9.4–350.6 15.9 2–63 43 9.3–16 5.64–1860 81.6 – 17.3 2.9–5.3 0.056–16.6 – – – Gil and Im (2014) Gill (2012) Larsson (2004) Kayhanian et al (2012) USEPA (2009b) Bold value: metals with high concentration in the railway industry 334–89,000 1000 358 P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 Compared to highway runoff, the concentrations of Cd, Cr and Pb were relatively low whereas Zn and Cu were typically high The concentration of Cu in railway runoff was significantly greater than the amount in roadway runoff, in some cases, up to 20 times higher Iron content in railway runoff has not been studied in existing research; however, its content in the environment is expected to be much higher than other metals (Wilkemirski et al., 2011) The toxicity of these metals has been widely studied Despite Cu, Mn and Zn being less harmful than Pb and Cr, they are more soluble, and so tend to have a greater impact on the water environment (Osborne and Montague, 2005) While the toxicity of iron is low, it can affect water colour and taste 3.2.5 Embankments 3.2.5.1 Soil erosion Erosion of rail embankments can result in a washing out of sediments These sediments themselves could be a source of pollution, depending on their particle size Furthermore, heavy metals and organic compounds tend to attach to particles As a result, particles may act as a medium for transporting pollutants into the water environment 3.2.5.2 Substitute materials for ballasts Steel furnace slags are often used as a substitute for natural rocks in the ballast layer Originating as a byproduct of the iron or steel processing industry, slag is a fused nonmetallic mixture which is rough surfaced and angular in external shape Steel slag is also highly resistant to physical and electrical forces These characteristics make steel slag a perfect candidate for railroad ballast Most practitioners consider slag to be an inert and safe material Yet, Piatak et al (in press) warned about the risks of slag usage Most notably, the content of Al, As, Cd, Cr, Pb and Mn content in iron and steel slag often exceeds the US EPA standards for residential and industrial soil Therefore, after interacting with air or water, derivative weathering products from slag can release trace metal elements such as Cd, Cr and Pb, especially under rainfall conditions This is the case when the quality of slag is not controlled 3.2.6 Human waste and littering In many developing countries, open carriage toilets are still being utilised in train cars Human excrement and garbage are discharged directly onto rail tracks and surrounding areas This waste often contains pathogens, nutrients and organic matter They are deposited and then accumulate in the environment without any treatment Representative cases can be found in many developing countries For example, with over 14 million people being transported via India's rail network every day, it was estimated that about 3980 MT of human waste were disposed freely from 160,000 open toilets per day (Comptroller and Auditor General of India, 2013) Moreover, railway corridors, which are commonly viewed as vacant land, become an attractive environment for illegal discharges of sewage and domestic waste 3.2.7 Maintenance facilities Maintenance activities take place at all railway depots Common contaminants in runoff water from these areas are oil and grease, chlorinated and non-chlorinated solvents, phenols, antifreeze, detergents, PAHs, sewage waste and several inorganic chemicals (Osborne and Montague, 2005) These pollutants have resulted from different processes in maintenance centres: metal processing, fuelling, repair of machines and batteries, maintenance of rolling stocks, train cleaning and so on Apart from a study by Gill (2012), information on the runoff quality from these areas is totally lacking 3.3 Pollution routes From the above analysis, the main pollutants in railway industries are PAHs, herbicides and heavy metals The possibility of runoff pollution is determined by numerous factors, such as precipitation regimes, runoff flow dynamics, substance properties and its interaction with surrounding soils (Fig 1) Rainfall is indeed a crucial factor in the environmental fate of contaminants It determines the movement of pollutants through rail tracks and embankments In general, ballast and subballast layers have much higher permeability than the subgrade Contaminants will be transported downward and normally retained at the interface between the subballast layer and the subgrade At low rainfall intensity (under 15–20 mm), rain water may accumulate inside the track bed The infiltration and evaporation rate might account for up to 75% of precipitation volume and sometimes does not generate the outflow of runoff (Burkhardt et al., 2005) Under high intensity rainfall, contaminants will be either washed out into drainage systems or infiltrated into adjacent soil Consequently, the retention time of pollutants in rail tracks fluctuates significantly, from half a day to three months from site to site (Osborne and Montague, 2005) The first flush effect was detected at locations that experienced great variation in wet and dry weather conditions (Gil and Im, 2014), but in places where the rainfall regime was more uniform, the first flush effect may not be observed (Lee et al., 2007) Secondly, the discharge of a contaminant into runoff is dependent not only on its sources and characteristics, but also on its interactions with the soil environment The unsaturated soil near the track bed could act either as a filter or a pathway to transport pollutants (Burkhardt et al., 2005) Flow dynamics in soil is determined on one hand by soil texture and structure, on the other hand, by soil water content and tension Two key mechanisms for the mass transfer of heavy metals and organic compounds are degradation and adsorption/ desorption Heavy metals are neither biologically nor chemically degraded They will accumulate in the track bed or in the surrounding environment Heavy metals tend to attach to silt materials in natural soil The adsorption of heavy metals on silt particles is influenced by pH Alkaline soil provides conditions advantageous for the adsorption of heavy metals, whereas acidic soil is favourable for desorption This typically increases the toxicity of the metals and their complexes For example, the low soil pH (pH = 4.03–6.38) in Chengdu–Kunming railway (Sichuan, China) showed the changes in Cd's mobile capacity (Liu et al., 2009) An interesting fact is that whereas most of the heavy metals in railway runoff are toxic, Fe and Mn could act as absorbents for attaching heavy metals and Emission sources Substances (Amounts, patterns, characteristics) Precipitation (Intensity, frequency, volume) Runoff (Track proϐile, drainage system) Mobility/ losses (Soil, track proϐile): Inϐiltration Degradation Sorption/ desorption Runoff pollution Fig The pollution pathway in rail track areas Modified from Burkhardt et al (2008) P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 anionic compounds such as glyphosate (Burkhardt et al., 2005) Nonetheless, their sorption capacities have not yet been investigated In contrast, organic compounds will degrade over time Their degradation is characterised by disappearance time (DT50) which varies greatly in relation to different types of environment In the case of rail tracks, the biodegradation of PAHs and herbicides is extremely low As Burkhardt et al (2005) observed, the microbial biomass in a track area is only one tenth of those in agricultural soil This could be explained by the coarse texture, low organic and nutrient contents of ballast and embankment materials Therefore, PAHs and herbicides used in railway embankments usually had better mobility and prolonged persistence (Cederlund et al., 2007) Many of these organic compounds are attached to organic matters in soil In favourable conditions, contaminants can be reactivated and released slowly over long periods of time The stormwater runoff then acts as a pathway to transport the contaminants from the soil into surface water bodies (Osborne and Montague, 2005) 3.4 Challenges in stormwater quality management in the railway industry Huge challenges have been encountered from the implementation of stormwater quality management in the railway industry Apart from common issues of stormwater management which were clearly addressed by Langeveld et al (2012) and Barbosa et al (2012), the railway industry experienced some particular struggles worth noting 3.4.1 Input data A lack of data is encountered as the most significant problem In reality, albeit the necessity of a thorough investigation on drainage systems both quantitatively and qualitatively, it is a tough task for any railway manager Not only is railway runoff quality data frequently unavailable, but documentation for stormwater drainage systems has also been inadequate (Singaraja et al., 2012) Historical modifications in storm drains were not recorded properly This is particularly problematic when it comes to predicting the movement of pollutants because they may distribute and end up at various unknown receptors The co-mingled effects of runoff between railway land-use and surrounding land-uses are another troublesome issue, especially under pressures of obtaining stormwater permits and abiding by surface water standards Some storm drain lines for the railway industry receive both stormwater falling on its own assets and from other facilities in the same watershed Furthermore, cross connections between different stormwater networks or between drainage and sewage systems make the situation more challenging (Dunning, 2012) 3.4.2 Monitoring and modelling Monitoring is a necessary step to determine baseline conditions, levels of contamination, treatment methods and management measures Key considerations for a stormwater monitoring program include 359 monitoring locations and safety, parameters and frequency, analytical methods, precision and accuracy as well as cost-effectiveness (Fig 2) Stormwater monitoring is more challenging than effluent monitoring due to the irregular nature of runoff, along with a substantial discrepancy of effluent throughout a rain event or time of discharge The number of events, the time and method of sampling during an event may lead to a striking contrast in results (Lee et al., 2007) Common sampling methods are instantaneous grab sampling and flowweighted composite sampling Although grab sampling is simple and cheap, it may distort the result of runoff quality, depending on the time of collecting samples (Lee et al., 2007) In contrast, flowweighted composite sampling gives a more precise outcome However, it is more complicated, costly and requires more training for practitioners Selection of the monitoring method should be based on practical conditions Nevertheless, grab sampling is still preferential in the railway industry To minimise the error in sampling, Leecaster et al (2002) suggested that the frequency for sampling be seven storm events per year, 12 samples per event using volume-weighted ratio Further discussion on the stormwater monitoring program could be seen in Lee et al (2007) The sampling of track drainage systems is classified as a high-risk task Safety issues may arise from either “adverse climatic conditions” or the potential harm of being struck by running trains The deficiency of clearly designated stormwater drains makes their monitoring even more troublesome (Copeland and Lefler, 2013) With regards to the lack of monitoring data on stormwater quality, a mathematical model is necessary for the prediction of its discharges on the environment (Barbosa et al., 2012) Several sophisticated stormwater quality management models have been incorporated with the consideration of treatment methods (Elliott and Trowsdale, 2007) Unfortunately, little information is available for movement kinetics of pollutants through rail tracks The application of available models for modelling railway runoff, therefore, needs further study in order to fine-tune and calibrate 3.4.3 Treatment challenges Besides uncertainties in stormwater quantity and quality, the selection of treatment methods faces various challenges First, space constraints are encountered in many types of railway infrastructures Railway corridors are often narrow but they accommodate a wide range of crucial infrastructures for daily operations such as power lines, communication cables, signalling systems, accesses, barriers and drainage systems This is also the case for many stations and stabling yards The restricted availability of land in the areas results in the limitation of treatment alternatives Maintenance frequency of treatment systems must follow the operational procedures of railways In fact, maintenance is a key issue for rail operations as anything within m of a live track can only be accessed during a possession This is when a section of the track must be officially Deϐine study type Determine study scope (Spatial boundaries, scale and duration) Consider sampling design issues Field sampling sites Spatial variablity Frequency Precision and accuracy Measurement parameters Fig Framework for stormwater monitoring Adapted from ANZECC and ARMCANZ (2000) Cost effectiveness 360 P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 shut down for works Because of this, maintenance requirements for drainage should not be any more frequent than yearly 3.4.4 Regulations, policies and standards As stormwater quality management in the railway industry is a newly emerging field, there is still debate as to whether railway runoff should be integrated into a general urban stormwater management scheme or be solely managed on its own On one hand, the inclusion of railway runoff into the general stormwater management program can reduce the cost of management and treatment On the other hand, it can be argued that each industry has to eliminate its own pollution and railway is not an exception It is necessary to reduce the level of metals and organic compounds which are specific in the industry Moreover, unlike other industrial sources, which have clear boundaries as well as outfalls for their assets, railway is mostly a line source (except at stabling yards or depots) which runs over different territories with various discharge regulations Every territory has its own permits, which poses a great challenge for a general control of stormwater quality in the industry, even though operational activities between different regions are similar Bench-mark standards for stormwater management are also subjected to a number of critiques as they are ineffective in controlling stormwater quality (National Research Council, 2008) Thus, a new methodology of allocating pollutant loads for different sectors in a catchment has recently been proposed to assist the enforcement of bench-mark standards (Rogne, 2012) The new calculation method is based on Total Maximum Daily Loads (TMDLs) for a catchment The railway industry is accordingly required to employ an integrated system of monitoring programs, stormwater control measures, appropriate modelling and treatment methods to adhere with this new approach (Schultz and Godlewski, 2012) In short, the accountability of stormwater management programs is often low With ambiguous understandings of the nature of pollutants in the railway environment, it is more challenging for rail companies to appraise whether their runoff water meets the given standards or not Provisions for stormwater quality management in the railway industry 4.1 Source control The pollution prevention measures are preferable in stormwater quality management in the railway industry To minimise the causes of pollution is more cost-effective than treating its consequences downstream as simple changes could lead to long-term positive results Common practices have been proposed to reduce pollutants at the source and prevent contact between stormwater and potential contaminants in the rail industry (US EPA, 2009a) However, these practices concentrated mainly on maintenance facilities and depots, rather than pollution along rail tracks, stabling yards and embankments Therefore, the following solutions are suggested for controlling potential sources of stormwater pollution for these areas As wooden sleepers are of most concern in relation to PAHs sources, they should be replaced by less harmful materials Gustafsson et al (2007) investigated the replacement of wooden sleepers with concrete sleepers Through their experiments, concrete sleepers were proven to be ecologically safe The only additive in concrete that attracted environmental concerns was sulphonate naphthalene With a concentration of 1‰ in the concrete, it showed an insignificant leaching rate (Gustafsson et al., 2007) Switching from wooden sleepers to concrete sleepers and composite sleepers (a new type of sleeper) becomes increasingly popular The application of herbicides in weed control practices should be carefully planned with regards to types of weed, time and amount of application, weed resistance capacity to herbicides and treatment locations The substitution of persistent and toxic herbicides for alternatives with quickly-degradable active ingredients is highly recommended A new technique of applying herbicides in the railway is to use lowspeed swiping trains These trains distribute herbicides directly onto specific weed-ridden areas at speeds of 5–8 km/h rather than spraying over entire areas, as is the present conventional method As Hansen and Clevenger (2005) argued, the disruption to natural soil conditions along railway edges promoted the invasion of exotic plant species Therefore, an additional method for controlling weeds that can be utilised is the re-plantation of indigenous flora (Victorian Rail Industry Environmental Forum, 2007) The preservation of natural vegetation on railway corridors also helps to reduce embankment erosion by increasing slope stabilities and eliminating water logging at the track toes In addition, mulches (organic and inorganic) could be utilised to reduce the growth of weeds A large quantity of metal deposits originated from abrasion processes of brakes, rails, wheels and power lines The magnitudes of deposits caused by these abrasion processes vary according to the type of materials involved; for instance, composite brakes and wheels emitted the least amount of metals, compared to cast-iron and sintered iron The substitution of cast-iron and sintered iron brakes by composite brakes could eliminate the emission of metals by approximately 90% (Gustafsson et al., 2007) As mentioned earlier, pollution along railway tracks is mainly accompanied with fine fractions It means that removing fine particles could reduce high fraction of impurities Therefore, increasing the frequency of ballast cleaning can reduce the accumulation of contaminants onto track beds 4.2 Stormwater treatment and harvesting 4.2.1 Stormwater treatment Although source control measures are effective in reducing pollution potentials, they alone cannot fulfil the requirements of stormwater discharge permits (Dunning and Weiner, 2011) In this case, a treatment system is necessary Unfortunately, the railway industry has not paid a great attention to stormwater treatment The judgement of selecting treatment methods must be based on understandings of quantity and quality characteristics of stormwater, treatment objectives, local conditions and possibilities for incorporating with educational or aesthetical purposes (Barbosa et al., 2012) National Research Council (2008) and Scholes et al (2008) provided systematic comparisons of different alternatives for stormwater treatment It is obvious that no single treatment method would be effective for removal of all pollutants Learning from experiences of highway runoff treatment, the conventional treatment chain often serves these functions: (1) trapping litter and large objects, (2) detaining coarse sediments, (3) settling fine sediments, and (4) treatment of dissolved solids and other contaminants In the case of the railway industry, space constraints and maintenance requirements are important factors in the selection of treatment methods Table reviews different methods in stormwater treatment and their applicability in the railway industry Constructed wetlands and detention basins, two common methods in urban stormwater treatment, would rarely be used due to limited space availability at railway areas Initial sizing of wetlands should be based on pollution reduction targets, but in reality, other factors such as topography may mean that excessive land area is required Sedimentation basins as a part of a wetland may have design particle sizes dictated by the catchment management authority The trapping of fine clay and silt particles makes basin size prohibitively expensive Simple methods such as buffer strips and grass swales are helpful in the removal of several pollutants The removal of contaminants by buffer strips is dependent on slope, length, runoff velocity, topography and vegetation type Buffer strips are suitable for removing coarse sediments and some finer particles such as heavy metals, PAHs and nutrients Stagge et al (2012) reported high removal efficiency for grass swales P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 361 Table Comparison of different stormwater treatment methods Modified from NSW Environment Protection Agency (1997) Targeted pollutants Scale of catchment Space constraint Environmental and community amenity Operational and maintenance requirement Litter and gross pollutants Coarse sediments Litters, coarse sediments Oil, coarse sediments b1 8–20 8–20 N1 Low Low Low Low Low Low Low Low Simple maintenance Simple maintenance Simple maintenance Simple b1 Moderate Moderate–high b2 Moderate Moderate–high Simple maintenance Slope of the strip b 5% Maximum flow depth = 12 mm Simple maintenance Sand filters Litter and gross pollutants, coarse sediments, suspended solids (SS), total phosphorus (T-P), total nitrogen (T-N), bacteria SS, T-N, T-P, organic matters, oil and grease, bacteria SS, T-N, T-P, bacteria 1–6 Low Low Infiltration trenches and basins SS, T-N, T-P, organic matters, bacteria b6 High Moderate–high Extended detention basins Coarse sediments, SS, bacteria N6 High Moderate Tertiary treatment Biofilters SS, T-N, T-P, organic matters, bacteria N/A Low Moderate Constructed wetlands Coarse sediments, SS, T-N, bacteria N6 High High Types of treatment Primary treatment Litter pits, baskets and racks Sediment traps Gross pollutant traps Oil/grit separators Secondary treatment Buffer (filter) strips Grass swales in treating highway runoff (50–60% of sediment, 46–81% of Zn, 27–75% of Cu and 41–72% of Cd) Analysis of data on the International Stormwater BMP Database roughly supports the figures by Wong et al (2000) with the exception of generally lower rates for TSS removal in swales Grass swales were very effective in removing zinc from runoff Stagge et al (2012) emphasised that in the cases of physical limitation as in railway corridors, the application of grass swales (about 200 m length) can significantly improve the effluent water quality However, finer sediments deposited during smaller flows may be remobilised during larger events Vegetation types must be carefully selected to prevent harmful effects on track foundation Infiltration systems often achieve moderate levels of pollutant removal due to the close contact between the runoff and substrate surface during the infiltration of the runoff through the media (Scholes et al., 2008), but they can have high failure rates Cleaning time is an essential factor in the design of these systems Wong et al (2013) advocated the use of biofiltration systems with a submerged zone for urban stormwater treatment The biofilters showed high removal efficiencies of TSS (N90%), pathogens (1–3 log for Clostridium perfringens, Escherichia coli, and F-RNA coliphages), heavy metals (N 90% for Cu, Zn, Cd and Pb), PAHs (N 80%), oil and grease (N95%) and glyphosate (N80%) (Bratieres et al., 2008; Li et al., 2012; Lim et al., 2015; Zhang et al., 2014) However, the biofilters were not effective in removing the triazine herbicides This was due to the short hydraulic retention time (3–5 h) of the biofilters (Zhang et al., 2014), which was insufficient for biodegradation of these herbicides Thus, there is a tendency to seek out novel filtration media to improve the capacity of removing pathogens, arsenic and micropollutants as herbicides For stabling yards, drainage systems have to move water away from the track formation quickly, denying the possibility of retention for filtering or sedimentation However, some stabling yards run in parallel to an access road, which may allow for the possibility of long narrow options such as grass swales, bioretention pits, and underground infiltration trenches For most depot sites, parking lots and stations, which are mostly impervious surfaces, filtration tanks could be located underneath In addition, bioretention could be reserved for landscaped garden beds in these areas Moderate maintenance due to sediment build-up May require pre-treatment Mostly suitable for sandy loam to loam soil type with the infiltration rate of 13–25 mm/h Simple maintenance May require pre-treatment Moderate to complex May require pre-treatment Moderate to complex 4.2.2 Stormwater harvesting To fulfil the goals of a sustainable transportation system, the railway industry aims to investigate opportunities for harvesting stormwater (Transportation for NSW, 2013) Compared to wastewater reuse, stormwater harvesting receives less public objections While most stations would not be able to incorporate any water storage under platforms due to structural elements and amount of services present, many would have space on the platforms for above-ground water tanks to capture rainwater from the station roofs In addition, a spacious area under stabling yards becomes an attractive opportunity for storing stormwater Australia is a pioneering country in this area, having constructed the largest underground stormwater storage system in a railway area Being constructed at Auburn station (Sydney) in 2011, the underground structure stores and treats more than 11,000 m3 of stormwater 4.3 Urban retrofit Urban retrofit is an innovative planning and design approach that considers the resilience of urban water that is aimed at developed or brownfield areas It fosters the incorporation of stormwater into the urban landscape for environmental, social and economic benefits Railway corridors are a promising candidate for urban designers to look for opportunities to incorporate natural elements and transform “vacant” space into liveable space As Penone et al (2012) discussed, railway could bear an ecologically functional connectivity in the fragmented urban context, especially when it runs across densely populated areas An example is the conversion of rail spaces to the green recreational belt “Green Rail Track” in Amersfoort (Utrecht, Holland) from 2011 to 2013 (Hoofwijk et al., 2013) Therefore, the wellplanned application of vegetated treatment methods along the tracks serves multiple purposes — reducing pollutant flux, providing structural connectivity for plant communities and integration of greenery into the grey infrastructure These outcomes look promising, not only in regards to its corridors, but also its green track application Green tracks for light railways have been very common in the UK, Germany, Netherlands and France In the study of Tapia Silva et al (2006), they assessed the ability of green tracks in reducing runoff volume by infiltration and 362 P.T Vo et al / Science of the Total Environment 512–513 (2015) 353–363 evaporation Nevertheless, the development of ballastless rail tracks provides a good opportunity for incorporation of green turf on the surface of concrete slabs Conclusion To the best of our knowledge, this is the first paper to review stormwater management practices in the railway industry This paper points out the changes in perception of stormwater management systems, from a drainage system (in the past) to a quality control (in the present) and a resource in urban areas (in the future) To date, the contamination of stormwater in railway areas has not been properly studied From the limited literature available, this paper tries to analyse potential sources of pollutants and their pollution pathways However, stormwater pollution and management levels vary from country to country Some pioneering countries, such as the US, the UK and Australia, have already issued relevant regulations and guidelines for controlling pollution from the railway industry This paper also addresses the managerial challenges and provides provisions for future management of stormwater quality in the railway industry From this study, we have found that there are many gaps in this field that are open to further research: – To survey stormwater quality from different assets of railway infrastructures such as rail tracks and embankments, stations, stabling yards and depots; – To model the transport behaviours and mass balance of pollutants through various types of track bed and embankments; – To explore the environmental fates of contaminants (PAHs, herbicides and heavy metals) under real railway conditions; – To investigate particle size distributions along rail tracks and their effects on the selection of treatment methods for stormwater; – To study different methods for treating stormwater in the railway industry Acknowledgements The authors acknowledge the Sustainable Water Program — Wastewater treatment and Reuse Technologies, the Centre for Technology in Water and Wastewater (CTWW), the School of Civil and Environmental Engineering, the University of Technology, Sydney (UTS) and UTS — Vietnam International Education Development Scholarship 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(quinoline, isoquinoline, indole and 2-methyl-quinoline) were leaked with a higher rate than that of PAHs The highest leaching rate was quinoline with 1050 mg/kg of wood after 24 h of submerging... obtaining stormwater permits and abiding by surface water standards Some storm drain lines for the railway industry receive both stormwater falling on its own assets and from other facilities in. .. stormwater management in the railway industry Rail tracks and supporting systems attracted the most attention in stormwater management plans for the railway industry as they were the backbone of railway