O następstwach składowania popiołów dymnicowych w pożwirowych wyrobiskach na tarasie Dunajca

Abstract

 Przedstawiono charakterystyki składu chemicznego naturalnych wód podziemnych i wód Dunajca oraz źródeł zagrożenia i oceniono wpływ składowania popiołów w wyrobiskach poeksploatacyjnych na jakość wód podziemnych w ich otoczeniu oraz możliwość zmiany jakości wód Dunajca. Substancje rozpuszczalne zawarte w masie składowanych popiołów są ługowane w procesie hydrotransportu i migracji wód osadowych w podłoże osadnika. Wody te uznano za silnie skażone. Drugim źródłem skażeń są wody opadowe infiltrujące przez zdeponowane osady już po zapełnieniu składowiska.

Określono je jako umiarkowanie skażone.

ON EFFECTS OF ASH DUMPING IN GRAVEL PITS IN THE DUNAJEC RIVER TERRACE

Dumped ashes (over 2 million cubic m in volume) are found to be the major source of pollution of natural groundwaters and surface waters in area of the dumps. The pollution is due to leaching of soluble matter (Na, Ca and Mg sulfates and chlorides, phenols, heavy metals and cyanides), proceeding in two stages: in the course of hydrotransport of ash to settling reservoir and percolation of surface water through the ash, and in the process of percolation of precipitation water after the end of dumping in a gravel pit.

In the studied area we have a single aquifer in sandy-gravel sediments (Fig. 2). Mineralization ranging from 640 to 1270 mg/dm³ is accepted as the boundary value for hydrochemical background of the waters (Fig. 3). Hydrochemical background values for in SO₄^2- fall within the interval 85–210 mg/dm³, and for ion CI^- – within the interval 22–140 mg/dm³ (Fig. 3). The waters are of the Ca-HCO₃-SO₄ type.

Waters of the Dunajec River, the major collector of the pollution, display sulfate background ranging from 22 to 62 mg/dm³ and that of CI^- ­– ranging from 8 to 25 mg/dm³ (Fig. 4). Concentrations of both  SO₄^2- and CI^- depend on water level in the river (Fig. 5).

Surface waters and those used in hydrotransport are of the SO₄-Ca or SO₄-Ca-Na type, with concentration of SO₄^2- varying from 31.9 to 423.1 mg/dm³ and CI^- from 12 to 172.5 mg/dm³ (Table 3). The waters percolate through ashes dumped in the reservoir, becoming saturated with additional amounts of soluble components, mainly sodium sulfates. Mineralization of pore water in ashes ranges from 850 to 2400 mg/dm³ and SO₄^2- content – from 540 to 1500 mg/dm³ (Fig. 6).

Content of chlorides generally remains the same as recorded in hydrotransport waters (35 mg/dm³ on the average – see Table 3), which indicates that all the chlorides became leached out already in the course of hydrotransport of ashes. The waters are of the SO₄-Na and SO₄-Na-Ca types.

The waters, yielding overnormative amounts of dissolved matter, sulfates and, quite unhazardous from the point of view of pollution, chlorides (Fig. 6), will subsequently supply groundwaters occurring beneath the dumps.

Possibilities of pollution of surface and ground waters by polluted hydro transport ones were quantitatively estimated on the basis of results of analog modelling. The analog studies made possible designing hydrodynamic network and, thus, the basis for estimations of migration of dissolved matter.

The above analyses showed that dumping of wet ashes in abandoned gravel pits under conditions of exploitation of the settling reservoir as given in Figs. 1 and 2 and natural, original pattern of hydroisohypses (Figs. 8, 9), should result in marked changes in quality of groundwaters. The spread of polluted waters into foreland of the reservoir may be stopped by a band drain made along dam. Depth of the drain and a natural slope of the area towards the Dunajec River should allow catching and directing large part of the contaminated waters directly to the river. The remaining strongly to moderately polluted waters would also flow to the river, in result of groundwater drainage.

The studies and calculations (Tables 4–7, and Figs. 10, 11) showed that the hazard of ground and surface water pollution is connected with the presence of dissolved matter, leached from the dumped ashes by surface and precipitation waters. The processes of leaching and migration of the matter to groundwaters should continue for the next 70–300 years. Under conditions of the designed dumping system, the pollution should be confined to an area delineated by the Dunajec River and the above mentioned band drain.

The drain should stop spreading of the pollution into the reservoir foreland, i.e. towards the existing village wells. However, this will be accompanied by a 1.0 to 1.5 m drop of water table in some wells. The inflow of polluted waters to the Dunajec River through the drain and aquifer is estimated at 170–240 dm³/s but this should not result in any marked changes in river water chemistry, thanks to high dilution.

When the designed conditions are fullfilled, the exploitation of gravel pit as a dump should not result in pollution of groundwaters in the proximity of village wells nor in change in quality class of water in the river.