Transfer of Contamination from Motorways Towards Karst Water Sources: The Example of the Malenščica Karst Spring

Abstract

A large part of motorways in Slovenia runs across the karst aquifers which are an important source of drinking water supply. Contamination washed off road surfaces by precipitation water can be a great threat to the quality of water sources. When the water, and with it harmful substances, enters the karst underground, it flows away rapidly through permeable karst channels and fissures towards the springs. Its cleansing ability, either natural or artificial, is very low, and the degree of endangerment of water sources is thus greater. Modern motorway construction has addressed this issue by building various protective facilities. The most frequent such facilities in the Slovenian karst terrain are oil separators with outflows from motorways leading into them. In practice, unfortunately, their operation has shown various deficiencies which has rendered the prevention or at least limitation of contamination rather unsuitable. In this chapter a study of the potential impact of contamination at the chosen motorway section on the regionally significant water source is presented. The conclusion provides a few general findings about the impact of motorways on the karst water sources and the necessary measures for their protection. During smaller inflows into the oil separator, the outflow from the oil separator into the karst terrain was usually of better quality than the inflow, and of significantly poorer quality during abundant inflows, since the sediment that had accumulated in the oil separator was also flushed out, and the majority of the organic contaminants and metals are tied to the sediment. It is thus necessary to ensure regular maintenance of oil separators and to properly clear out the accumulating sediment. For individual oil separators on motorway sections on the Karst, tracer tests are a sure method to determine and evaluate the link with drinking water catchments. Where a direct link with high flow rates was determined, it would have to be provided effective treatment of waste water before it is released into the karst terrain. On the other hand, if no such detailed research was carried out in the recharge area of the karst water sources, it would still be necessary to intercept and properly treat at least initial quantities of the most contaminated outflow water from the road surfaces.