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Maximovich N.G., Kazakevitch S.V., Khmurchik V.T., Nikiforov V.V. Oil pollution of the hydrosphere of karst areas // Актуальные проблемы геохимической экологии: Материалы V Междунар. биогеохим. Школы (8-11 сент. 2005 г.). Семипалатинск, 2005. С. 374-375.

OIL POLLUTION OF THE HYDROSPHERE OF KARST AREAS

N.G. Maximovich, S.V. Kazakevitch, V.T. Khmurchik, V.T. Nikiforov

The hydrosphere with highly karstified rock development is prone to pollution. The areas of oil deposits appear to be most vulnerable to transformation. The contamination with oil products, surface active agents and various chemical reagents alter the composition of ground and surface water as well as soils and rocks. Misoperation of boreholes may disturb the hydrodynamic and hydrochemical regime of ground water and may favor its overflow from one aquifer to another. Although groundwater is more difficult to contaminate than surface water, reclamation of contaminated aquifers will also be much more difficult.
Perm region occupies an area of about 160 thousand sq.km. The karstified rocks, i.e., limestone, dolomite, gypsum, anhydrite, and Paleozoic rock salt, are either exposed or lie close to the surface in the area of about 30 thousand sq. km. The deposit area is situated in the central part of Perm region within the Polazninskii site of Polazninskii karst region (predominantly of gypsum and carbonate-gypsum karst). This area encloses the left coastal side of the Kama water reservoir. 1691 karst forms are mapped within the area of 28,1 sq. km, 97% of them being sinkhole. Other surface forms, such as karrs, karst trenchs, hollows, gullies, dry river channels and lakes are also registered.
Karst development in the region was promoted by the formation of Kama water reservoir in 1954, which induced the water level rise by 20-22 m. Filling the reservoir with water the project level in spring and the water level fall by 6-8 in winter changed the hydrodynamic zoning of karst water and favored the recurrent ingress of weakly mineralized water to the rock massif. The bulk of karst cavities occur within the zone of seasonal fluctuation of fractural-karst water. Dissolution and leakage most intensely develop within the drainage surface interval, i.e., in the upper 6-8 m of the aquifer. The existing karst forms are renewed and new ones appear.
Perm region is one of the areas of oil-deposits development. A considerable part of them is located within the drainage zone of the Kama River. The Polaznenskoe oil deposit is an example of such an area, where oil lenses were formed at the groundwater surface during its 50-year-long development. Contaminated groundwater discharge into the Kama water reservoir. There are three zones of intensive groundwater discharge as a springs in winter and subaquatic way in other time.
The analysis of geological and hydrogeological information proved that oil discharge on the coast is related to the long-term operation of oil deposit. The intense karstification in the area appears to be one of the principal natural factors that provided the development of oil pollution source at the surface of fracture-karst water. The studied site is specified by a number of peculiar features caused by karst development, which favors the contamination of the groundwater with oil products. Above all, the surface runoff is virtually absent. Atmospheric precipitation as well as oil spills are freely absorbed by rock fractures, funnels, depressions, and other karst forms to feed aquifer soon. This is a specific feature of the given oil deposit. At other oil deposits, where the environmental conditions are different, the oil spills contaminate, above all, the surface water, soil, and rock in the aeration zone, and next, the ground water.
To study the oil lens, the regime observations in boreholes were performed. This monitoring testified to almost similar water level in the Kama water reservoir and boreholes drilled 50-400 m far from the shore. This points to their close hydraulic connection due to the high level of rock karstification.
Two methods of pollution control in the Kama water reservoir were used taking into account the geological and environmental conditions at the deposit: pumping oil out the lens using special technique and the biochemical destruction of oil using the natural biodegradation on the basis of oil-degrading bacteria activation in groundwater.
The groundwater provides a habitat for bacteria. Microorganisms in groundwater are active in situ, and therefore play a significant role in influencing groundwater chemistry and quality. A great number of subsurface environmental factors can influence microbial activity and therefore also the transformation of pollutants: temperature, pH, redox potential, availability of electron acceptors, salinity and hydrostatic pressure, porosity of the aquifer's rocks, chemical recalcitrance and solubility, chemical and physical adsorption and desorption on rock particles. Microorganisms found in groundwater are able to transform a large number of contaminants under the existing redox conditions. The presence of sufficient electron acceptors will be a principal factor in predicting the degradation of organic contaminants in aquifers. Other elements like Mg, K, Ca and trace elements necessary for microbial growth are usually available in concentrations high enough to support microbial growth.
The most common pollutants of groundwater are hydrocarbons and heterocyclic compounds of oil and oil-products. There are two main biotechnological methods of oil polluted natural habitats remediation: 1) the stimulation of natural microbial hydrocarbon-oxidizing populations by nutrient supplies (especially N and P), and 2) the introduction of active hydrocarbon-oxidizing bacteria (and nutrient supplies) into polluted environments. We try to combine these approaches to achieve the cleaning up of oil-polluted karstic aquifer. Our work consists of several stages: the isolation of active hydrocarbon-oxidizing bacteria from karstic groundwater and the study of their oil degrading capability; the development of bacterial preparation based on isolated aboriginal hydrocarbon-oxidizing bacteria to remediate oil polluted groundwater; the stimulation of aquifer's hydrocarbon-oxidizing microflora by inorganic nutrients supplies; and the introduction of developed bacterial preparation into aquifer to achieve complete oil removal. It must be noted that the introduction of actively metabolizing hydrocarbon-oxidizing bacteria into polluted environments is essentially actual in regions of cold and temperate climate, where warm season is not long.
Thus, the study performed showed that the intense karstification of the rock massif is one of principal natural factors that resulted in the development of oil lens at the karst water table discharging to Kama water reservoir. Microbiological investigation of karstic groundwater revealed the presence of active hydrocarbon-oxidizing bacteria which can be used in the development of bacterial preparation to cleaning up oil polluted aquifer.
The work was financially supported by the Russian Foundation for Basic Research, project "Ural-2004", no. 04-05-96039 and the Scientific program "Development of Science potential in Higher school" of the Federal Agency on Education at the Ministry of Education and Science of the Russian Federation, grant no. 49181.


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