Assessment of threats connected with contamination of groundwater with mercury due to impact of selected road sections in central Poland

Praca podejmuje temat zanieczyszczenia rtęcią przypowierzchniowej warstwy gruntu w otoczeniu tras samochodowych, na odcinkach, gdzie przewiduje się potencjalną możliwość negatywnego oddziaływania na wody podziemne, zlokalizowane w utworach o charakterze porowym (wieku plejstocen - holocen). Dla oceny zagrożenia, przeprowadzono próbę oceny czasu pionowego przesiąkania zanieczyszczeń z powierzchni terenu do wód podziemnych na danych obszarze. Podjęta problematyka jest słabo rozpoznana, a jednocześnie bardzo aktualna w polskich warunkach ze względu na możliwe zagrożenie środowiska, związane z budową nowych odcinków autostrad i dróg szybkiego ruchu.The work includes an analysis of mercury contamination of top soil horizons in the immediate vicinity of transportation routes which may potentially have a negative impact on subterranean waters in porous sediments. Research included areas in the vicinity of the MGWB 141 (impacted by the national road 1, section from Toruń to Chełmża) and the MGWB 150 (impacted by the national road 2, section from Konin to Koło). The conducted studies allow a supposition that the utilisation of transportation routes results in slow cumulating of mercury compounds on the sides of the roads and in soils in the surrounding areas. The total mercury concentration level in the analysed soils generally ranged from 0.03 to 0.04 mg/kg of dry sample mass. If the clay fraction is bigger, the content of mercury increases even further. A significant element of the work is the threat assessment for groundwaters resulting from contaminant migration from top horizons of the soil. Problems associated with the susceptibility of groundwaters to contamination were presented in the aspect of the average time assessment of contaminant migration from the top horizon to the water-bearing horizon, i.e. aeration zone filtration time. It has been assumed that the relatively unthreatened groundwater reservoirs are those which have an average of 25 years for vertical migration of water from the top horizon. The assessment of vertical filtration time follows from the formula applied. The vertical migration time of waters potentially contaminated via the aeration zone was assessed using the Bindeman formula and the Bachmat and Collin formula (used by Witczak and Żurek). The assessment was further supplemented by results obtained using Macioszczyk's suggestion which combines the guidelines in the earlier formulas. The threat of contaminating compounds, and especially mercury, was assessed for selected segments of roads, which had earlier been analysed for the contaminant level in the top horizons. The applied formulas give different values of filtration time through the aeration zone. Considering the conservative water marker migration time, the analysed groundwater reservoirs were threatened no matter which formula was applied. In case of mercury, the level of threat follows from the accepted value of index delay related to sorption processes