Proceedings_Theme_01_Proceedings IMWA 2011 22/08/2011 12:36 AM Page 65 Aachen, Germany “Mine Water – Managing the Challenges” IMWA 2011 the exploitation of lignite deposits in relation with the surface and groundwater in the mining area — the case study of potamia basin, thessaly, greece Eleni Vasileiou, Ioannis Koumantakis National Technical University of Athens, School of Mining Engineering-Metallurgy, Section of Geological Sciences, Laboratory of Engineering Geology & Hydrogeology, Heroon Polytechneiou 9, 15780, [email protected], [email protected] abstract The aim of this paper is to investigate the correlation of water resources and exploitation of lignite deposits. This research took place in Elassona basin, in Thessaly, where two lignite deposits have been found, but the exploitation of them has not started yet. Multiple criteria have been analysed (geological, hydrogeo- logical, hydrological, hydrochemical etc) with the purpose of estimating the changes that will be caused during the mining activities in the area. The difficulties that the surface and groundwater cause to the lignite ex- ploitation are also examined. Key Words mining, aquifers, hydrogeology, surface run-off, groundwater Introduction • The Paleozoic gneiss with acid intrusions of Elassona basin is located in Thessaly, Central granites, which forms the western boundary of Greece. It is crossed by the Titarisios River, which the basin. drains an area of 107.75 km². The geological base- ment of the basin belongs to the Pelagonian Hydrogeological settings Zone.. In Potamia basin, (Elassona –Thessaly), two Hydrogeological conditions of this area deter- lignite deposits of 187.5 × 10⁶ tn (Domeniko: 167 × mine the exploitation or not of these deposits. 10⁶ tn and Amourion: 20.5 × 10⁶ tn) have been The area is covered by Quaternary and Neogene identified (Dimitriou 1997). The exploitation of deposits, in which the permeability varies. these two lignite deposits will result in changes of Potamia basin is more or less surrounded by im- the natural and human environment of the pervious formations, schists, gneiss-schists and area.For the understanding and estimation of the gneisses, which form impermeable boundaries. environmental impacts that will incur from the (Beloukas 1988) The overlaying marbles of the prospective lignite exploitation, the evaluation of Pelagonian series are of limited extend and thick- the current hydrogeological, hydrological, geo- ness, especially in the area of Evagelismos and in morphological characteristics and the land use is the basement of the basin, the total recharge vol- of great interest. Specifically, the water balance, hy- ume of it was estimated at about 3 × 10⁶ m³/year. drometeorological data, quantitative and qualita- So they are of minor importance concerning their tive analysis of the drainage networks of the area water storage capacity. In the same formation, were studied. In this paper we compare the cur- south of Domeniko, groundwater flows mainly to rent status in the area to that existing 30 years ago the east and has a discharge point out of the basin. and anticipate the trend in the future. At this time The only karstic formartion of major importance there are no specific plans for the exploitation of is the one of the autochthonous series north of Ke- these two lignite deposits, the research is in pre- falovriso (karstic massif of Krania). Groundwaters liminary stage. have significant recharge from infiltrations, perco- lations of rivers, torrents and karstic volumes geological settings (Manakos, 1999). The basement of the Neogene basin of Elassona The springs at Kefalovriso (40 × 10⁶ m³/year) geotectonically belongs to the ‘’Pelagonian Zone’’ with an average flow of 1.3 m³/sec is the main dis- (IGME sheet, 1987). It consists of (figure 1): charge point of the above mentioned karstic aquifer (figure 2). These marbles as well as the • Marbles of the middle Triassic, which form the Titarisios River are the main sources of recharge north outcrops near Evagelismos and Paleokas- for the aquifers of the filling of the basin at the tro and part of the south-east boundary of the northern boundaries of it. It was estimated that basin, near Domeniko. They also have been an average quantity of 28 × 10⁶ m³/year, are perco- penetrated by some boreholes in the basement lated in the karstic mass of Krania (Vasileiou 2011). of the basin. There is also rich surface run-off. The springs • Schists, gneiss-schists and gneisses, which un- at Amourio area (figure 3; 13 × 10⁶ m³/year), in the derlay and form a ‘’ring’’ around the above alluvial sediments of the basin. Additionally, the mentioned karstified marbles. basin is crossed by Titarisios River (109 × 10⁶ Rüde, Freund # Wolkersdorfer (Editors) 65 Proceedings_Theme_01_Proceedings IMWA 2011 22/08/2011 12:36 AM Page 66 IMWA 2011 “Mine Water – Managing the Challenges” Aachen, Germany Figure 1 Simplified Geologi- cal map of the Potamia basin. nah claunnA nah oegn f d iegrahcsi Kn sosurvolafe nirp (sgn )8002-2791 55, 05, 5,4 )ce/s 0,4 3 5,3 m (egrahcisD m nMi 0,3 xMa 5,2 egraevA 0,2 51, 01, 5,0 Figure 2 Diagram of dis- 0,0 charge fluctuation in Ke- falovriso springs. raYe Changes of dis c harge in Amourio s prings (1972-2008) 2,8 2,6 2,4 2,2 2,0 1,8 min /s e c ) 3 1,6 max 1,4 average 1,2 1,0 0,8 Dis c harge(m 0,6 0,4 0,2 Figure 3 Diagram of dis- 0,0 charge fluctuation in 2 4 6 8 4 6 8 0 2 4 6 8 82 88 9 9 9 0 0 0 0 0 97 97 97 97 1 1 1 1 1980 19 1984 1986 19 1990 1992 19 19 19 20 20 20 20 20 Amourio springs. Year 66 Rüde, Freund # Wolkersdorfer (Editors) Proceedings_Theme_01_Proceedings IMWA 2011 22/08/2011 12:36 AM Page 67 Aachen, Germany “Mine Water – Managing the Challenges” IMWA 2011 m³/year), which is developed by the conflux of area there is expected recharge from the river and Boulgari and Elassonitikos Rivers. The annual rain the Quaternary deposits. A net of wells drainage fall in the area, is about 549 mm/year. The total will be necessary in this area, to ensure the right amount of evaporation is very high in about 80%, exploitation of the deposits. the percolation is about 12% and the surface run Amourio lignite field has different hydrogeo- off 8% (Vasileiou 2011). The recharge of the basin logical characteristics, Titarisios River crosses the is supported additionally by the infiltration of the lignite field in Amourio area and the diversion of rivers. The recharge from Boulgaris and Elassoni- it is necessary, which highly increases the finan- tikos rivers is rich, because it comes from other hy- cial cost of exploitation. The geological forma- drological basins in higher elevations, in which tions (coarse grained materials and fluvial the rainfalls are higher. Boulgaris River has addi- terraces) have higher percolation than Domeniko tional supply from the Kefalovriso springs and area. Significant is the recharge in this area, along some small torrents in the west boundaries of the the river, because of the infiltration of Titarisios area. In figures 2, 3 it is obvious that Kefalovriso and the percolation (figure 5). This will cause slope springs have a big capacity, even though there is a stability and dewatering problems. The uncon- decrease during the period 1973—2008. The dried fined aquifer has significant capacity and high up rate (Maillet, 1905), a=10⁻² d⁻¹, shows that this water heads have to be confronted in the floor of karstic system is drained very quickly. On the con- the open pit. The high discharges in the artesian trary Amourio springs have value of dried up rate wells of this area (250 m³/h and 100 m³/h) must about a=10⁻³ d⁻¹, which means that this is a very be considered. Additionally there is continuous good hydraulic system, with normal operation recharge from north and east to south due to the (Vasileiou, 2011). piezometry of the basin (Vasileiou 2011). In Potamia basin, two aquifers are developed, Several chemical analyses were executed in the one unconfined aquifer overlying of lignite de- area (50 water samplings) and the evaluation of posits, that has low capacity and one confined them showed that the water is of good quality, aquifer underlying. In Domeniko sub-basin, the without any specific problem; this is a very inter- upper unconfined aquifer will be totally drained esting element, because Thessaly has to confront due to the exploitation of lignite. The average very intense problems with nitrate pollution. In thickness of it is about 100m and the capacity is the area of lignite field of Domeniko, high conce- low. The transmissivity values are about 10⁻⁴– trations of Mn⁺² have been measured, because 10⁻⁵ m²/sec, which are approved from the low well there are abandoned mines of manganese in the discharges (30—40 m³/h). The hydrostatic pres- area (Vasileiou et.al. 2004). sures from the confined aquifer will be significant The area has two main characteristics, the ex- in the areas that the thicknesses of lignite de- tended agricultural activities and the over ex- posits are very small, the average thickness of this ploitation of the water resources for covering the aquifer is about 60 m and the discharge is about irrigation and potable needs. A volume over 20—30m³/h (figure 4). This happens only in the 9.5 × 10⁶ m³/year is pumping from the drills, west boundaries of the mine, in the central area mainly along the River Titarisios and Amourio of the basin near to the River Elassonitikos. In this springs area (Vasileiou 2011). Figure 4 Schematic section of Domeniko area.