Pollutant emissions from roads and traffic present risks and hazards to water bodies where roads are in their recharge area or when they are in direct contact with road environment. Risk is defined as the probability that a particular adverse event will occur during a stated period of time, or it results from a particular challenge (Adams, 1995). Similarly ‘hazard’ is defined as the attribute that is the consequence of the probability of an adverse event and the degree of harm that can happen if this event occurs. A high hazard is present where the potential consequences to water bodies are significant.
Pollution risk depends not on vulnerability but on the existence of pollutant loading entering the subsurface environment. It is possible to have high aquifer vulnerability but no risk of pollution, if there is no pollutant loading; and to have high pollution risk in spite of low vulnerability, if the pollutant loading is exceptional. It is important to make clear the distinction between vulnerability and risk. This is because risk of pollution is determined not only by the intrinsic characteristics of the aquifer, which are relatively static and hardly changeable, but also on the existence of potentially polluting activities, which are dynamic factors which can in principle be changed and controlled.
The hazard of polluting the proximal road environment is the consequence of three types of emissions that are very much related to overall road and traffic characteristics:
• permanent emissions;
• incident emissions; and
• seasonal emissions.
Permanent emissions are mainly the consequence of vehicle operation on the road and their interaction with the pavement. This type of emission can also be the consequence of the interaction between materials used for road construction, maintenance and their surrounding environment.
Seasonal emissions are the result of the climatic seasonality, which influences circumstances that exist at a particular time on pavement and in the embankment. Typical seasonal emissions are connected with road salting. In northern European countries and Alpine countries during the thawing of snow and ice, a significant amount of chloride is emitted from the roads and their near surroundings. Similar seasonality is connected with higher summer temperatures when pollutants are more bound to asphalt surfaces then during the colder periods of the year.
Accidental spillages of liquids and gases hazardous to water bodies are typical incident emissions on roads. Roads, where the potential hazard of spillage of environmentally dangerous goods is high, should be treated more rigorously than roads where such potential is small.
Protecting the water environment from different types of emissions requires different mitigation measures. Therefore, it is necessary that during the planning and design of roads, a basic knowledge about potential risk and hazards must be established.
