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It is commonly assumed that construction of tunnels would have positive impacts on the environment since it would reduce noise pollution and visual intrusion caused by infrastructures. However, as trends show, traffic is expected to increase in Australia and across the world in the next few decades; naturally, it is important to consider the impact of tunnel construction on air pollution and other aspects of the environment. The air pollution caused by tunnel construction could be segregated into two kinds – one, the pollution inside the tunnels owing to traffic jams and the transportation of hazardous material and two, pollution outside the tunnel (Bari and Naser 2010). The following paper attempts to highlight the major pollution related issues associated with tunnel construction.
With the number of vehicles increasing as shown in the graph bellow, traffic is expected to increase at an alarming rate in the upcoming years, which is bound to affect the quality of air within the tunnel (AECOM Australia 2014). Road traffic would result in excessive vehicle emissions which would adversely affect air quality and temperature in a confined space like a tunnel. Such traffic would increase the concentration of air pollutants, which are often hazardous. As a matter of fact, these tunnel emissions do not simply affect the air within the tunnel, but also have an impact on surrounding environment. In the case of long tunnels, heat emitted from vehicles would increase the temperature within the tunnels beyond the optimum levels; this is all the more poignant since most tunnels in Australia lack a strong ventilation system. Moreover, it has been found that construction activities involving tunnels are one of the major sources of noise pollution in Australia. Measures would have to be taken to reduce the generation of noise at the very source; this would include the use of sound proof barriers, sound insulating barriers and noise absorbing pavements.
(Figure: Estimate of traffic in Australian cities)
The most common air pollutants which are released into the air by vehicles include nitrogen oxides, carbon monoxide, particulate matter and hydrocarbons; all of these are components of vehicular exhaust (Bari and Naser 2010). Out of all these pollutants, it is estimated that nitrogen oxides, which includes nitrogen dioxide, are responsible for more than 70 per cent of the pollution. Vehicular exhaust mainly consists of OC or organic carbon and EC, which can together reduce visibility within the tunnel. Additionally, excessive quantity of hydrocarbons and nitrogen oxides could lead to aerosols and secondary ozone formation (Dominici et al. 2013). It has been found that these air pollutants can lead to cardiovascular problems and respiratory diseases in human beings when exposed to them. The purpose of tunnels is to redirect traffic so as to reduce congestion caused by the same. However, most tunnels in Australia lack a proper ventilation system; this means that the pollutants caused by vehicle emissions remain in the tunnel itself with no outlet. More importantly, it has been observed that the exhaust gas accumulated within the tunnels is often diffused into the main city without treatment; depending on the exhaust gas velocity and certain other meteorological parameters, this could increase the amount of pollutants in air (Font et al. 2014). In Sidney, an analysis of the quality of air inside tunnels has shown the presence of certain toxic ultrafine particles which are a direct consequence of fuel combustion. The truth is, such ultrafine particles are present in moderate amounts in urban cities; however, in tunnels without a proper ventilation system, the concentration levels are a 1000 times higher. These particles are potentially life threatening and could lead to myocardial infarctions and other respiratory problems in people exposed to such air (Costa et al. 2017). It has also been found that vehicle emissions from old cars are a leading source of such particles.
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(Figure: Concentration of pollutants in Sidney)
It is commonly assumed that transporting hazardous material through road would be safe; as a matter of fact, it is believed that it would be safer to transport such hazardous material through diversions like tunnels, since it would reduce exposure to main cities. However, this would increase the chance of risk to travelers using the tunnels and might even cause irreversible damage, as far as the tunnel itself is concerned (Bubbico et al. 2009). Moreover, most of these tunnels in Australia are located in residential areas; using tunnels to transport hazardous material would thus mean exposing residential areas to such toxicity. Additionally, during transportation of hazardous material, there is always a remote possibility of accidents and mishaps; in such a case, the tunnel environment and that surrounding it might be exposed to toxic and inflammable materials. This might lead to further disasters like pool fires, explosions or flash fires (Nicolet-Monnier and Gheorghe 2013). This might adversely affect the people traveling through the tunnel or residents belonging to the local community. Before transporting hazardous through tunnels, it is important to consider the following factors –
- The chances of damage to the tunnel due to explosions or fires must be relatively small.
- Adequate measures must be taken in order to minimize damage. This could be done through installation of water seals, making pump chambers immune to explosions, heat proof wall coatings and so on.
- Adequate measures also need to be taken in case emergency situations arise; for example, protection in case of a fire, escape routes, communication facilities et cetera.
There has been extensive research on the impact of tunnel construction on air pollution, mainly caused by vehicular exhaust and emissions. However, there has been little research on the environmental impacts of tunnel construction on groundwater flow. During construction of tunnels, there are many issues pertaining to inflow of water which prove to be a hindrance for construction workers and designers. In Australia and around the world, numerous tunnels are being constructed because it is assumed that this would lead to efficient transport; however, tunnels often interfere with the groundwater of the location, especially with respect to carbonate karstic rocks (Li et al. 2016). This would not only have a massive toll on the environment but also pose a serious problem for construction workers since it could create unsafe conditions and increase construction costs.
Conclusion:
To conclude, it can be said that although tunnels were mainly constructed with the aim of reducing traffic, tunnel construction has emerged as one of the major sources of air, water, noise and groundwater pollution. Vehicular emissions have contributed to most of the pollutants present in air, including particulate matter, hydrocarbons and nitrogen oxides. At the same time, transportation of hazardous material through tunnels could prove to be risky, since there is always a threat of accidents and explosions. However, it must be asserted that research is lacking in terms of the effects of tunnel construction on groundwater; construction of tunnels could have severe environmental, geotechnical and hydrogeological impacts which must be taken into account.
References:
AECOM Australia Pty Ltd 2014, Environmental Impact Statement: NorthConnex Submissions and preferred infrastructure report, Sydney, section 2.4-2.7 (pp. 51-99)
Bari, S. and Naser, J., 2010. Simulation of airflow and pollution levels caused by severe traffic jam in a road tunnel. Tunnelling and Underground Space Technology, 25(1), pp.70-77.
Bubbico, R., Di Cave, S., Mazzarotta, B. and Silvetti, B., 2009. Preliminary study on the transport of hazardous materials through tunnels. Accident Analysis & Prevention, 41(6), pp.1199-1205.
Costa, L.G., Cole, T.B., Coburn, J., Chang, Y.C., Dao, K. and Roqué, P.J., 2017. Neurotoxicity of traffic-related air pollution. Neurotoxicology, 59, pp.133-139.
Dominici, L., Guerrera, E., Villarini, M., Fatigoni, C., Moretti, M., Blasi, P. and Monarca, S., 2013. Evaluation of in vitro cytoxicity and genotoxicity of size-fractionated air particles sampled during road tunnel construction. BioMed research international, 2013.
Font, A., Baker, T., Mudway, I.S., Purdie, E., Dunster, C. and Fuller, G.W., 2014. Degradation in urban air quality from construction activity and increased traffic arising from a road widening scheme. Science of the Total Environment, 497, pp.123-132.
Li, L., Tu, W., Shi, S., Chen, J. and Zhang, Y., 2016. Mechanism of water inrush in tunnel construction in karst area. Geomatics, Natural Hazards and Risk, 7(sup1), pp.35-46.
Nicolet-Monnier, M. and Gheorghe, A.V., 2013. Quantitative risk assessment of hazardous materials transport systems: rail, road, pipelines and ship (Vol. 5). Springer Science & Business Media.
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