In recent years, it has been demonstrated that diffuse or irregular sources of pollution, like runoff, constitute significant contamination points in the natural drainage system. In most cases one has to take appropriate measures to control this pollution. In general, the environmental aspect of a road project nowadays constitutes an integral and fundamental part of the project, so that there is a strong interdependency between the various aspects considered in design and in the interventions that have
to be planned. In particular, it will probably be necessary to perform an integrated assessment of the road project itself, the drainage, the water resources, the quality of the water, the geology and the geotechnical aspects, with special focus on hydrology and landscape studies. Only in this way can one balance need for the road and the impact it will cause and allow the design, dimensioning and implementation of optimal and adequate systems for the conveyance and treatment of water flowing from the road platform.
The choice of treatment system to adopt has to address diverse conditions:
• the type of pollutants to treat (in particular heavy metals);
• the regional climate;
• compatibility with the roads’ drainage project;
• the impacts on the landscape; and, also
• the creation of a passive system, without the need of energy which, thereby, has great reliability and low maintenance needs.
Therefore, once the discharge points have been associated with particular, sensibly- sized, areas of the pavement platform, one can compute the discharge and proceed to study which treatment system should be adopted and its interaction with the drainage system.
The implementation of a project of this kind doesn’t overcome the need for an effective control of the treatment efficiency and this may be achieved through the application of an adequate monitoring system for the site. This should commence operation immediately after the start of the road use. Data can be obtained by sampling the pollutant charge in the runoff on first use. It will form a baseline against which to check any eventual flaws in functioning of the recovery and treatment system. Monitoring will allow the operator to detect, and thus rectify, any defects in a timely manner. The successful implementation of a sampling program of this nature will be very useful not only for the scheme in view, but especially for new situations, helping to find better project options which can be implemented in subsequent projects.
In parallel one should promote periodic maintenance and conservation action in the drainage network and in the treatment areas. In fact, without adequate maintenance the investment made will be likely to prove fruitless.
