Reloading of the toxic and other materials at the marshalling railroad yard, situated in vicinity of the main Belgrade groundwater supply resource “Makis“, can be very risky regarding the possible pollution of the groundwater, since the covering protecting clayey layer is relatively thin and the groundwater level very shallow. In 1987 the accidental leakage of the dimethylbenzene, C6H4(CH3)2, led to a serious contamination of the groundwater which had to be detected and monitored due to the possible migration of the pollutant towards the water supply wells as well as downwards to the main hydrogeological aquifer, consisting of the alluvial sands and gravel, at the depths ranging from about 15 to 25 meters. The covering layers of the Sava river alluvion, made of sands and sandy or silt clays, are also highly permeable making the direct path for the migration of the pollutant downwards. The first wells drilled in October 1987 indicated the presence of the very thin clayey protecting layer of about 2-3 metres. On the other hand groundwater level ranged from about 1 meter at the railroad embankment to about 2.5-4.5 meters outside the marshalling railroad yard, which was founded on the artificial sandy cover, 2-3 meters thick. The natural soil is separated by the drainage channel from the railroad yard, thus partially preventing the horizontal migration of the pollution towards the water supply wells at the shallower depths. The downward migration of the contaminant is mainly controlled by the natural permeability of the alluvial sediments. During the last eleven years the great number of the shallow (3.5-4 meters deep) monitoring drills were bored in the immediate vicinity of the accidental site together with regularly spaced deeper (to about 30 meters) drills, which were mainly placed outside the railroad marshalling yard due to the possible direct contamination of the main deeper laying aquifer. Monitoring has been performed by making chemical analysis and by measuring the conductivity and temperature of the groundwater at different depths and in different seasons. Conductivity measurements, performed in 1995 and 1997, indicated high values up to 4900 μS/cm in the source of the pollution with the general lowering trend towards water supply wells to about 800 μS/cm. This fact gave the opportunity to test the resistivity scanning method as the nondestructive method for monitoring of the pollution which, on the other hand, can give detailed information about the lateral extent of the contaminant plume. Drill holes can give the exact information about the vertical extent of the contamination but fail to fulfil the necessity of getting sufficiently detailed information about it’s lateral extent depending mostly on the lateral lithological variations.


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