Лаборатория геологии техногенных процессов
Gorbunova K.A., Maximovich N.G., Kostarev V.P., Andreichuk V.N. Technogenic impact on the Karst in Perm region// Studia carstologica.-1990.-N2.-P.37-43. /0,4/
TECHNOGENIC IMPACT ON THE KARST IN PERM REGION
K. A. Gorbunova, N. G. Maximovich, V. P. Kostarev, V. N. Andreichuk
G.K.W.: environmental changes, human impact, mining, solid wast deposits
Geogr.K.W.: USSR, Perm region, Pre-Urals, Urals.
The human impact in karst regions leads to significant changes in all elements of environment: soils, rocks,surface and ground waters.
SPREAD OF KARST
The Perm Region territory of 160,6 sq.km is situated within three large geostructures: the eastern margin of the Eastern European platform, Pre-Urals foredeep and the folded belt of the Urals zone. The karstic rocks: limestones, dolomites, gypsums, anhydrites, salts Paleozoic are exposed or occur not deep from the surface on the area of about 30 thousands sq.km (Maximovich G., Gorbunova K.,1958). Numerous boreholes in the carbonate rocks have revealed ancient karst.
In the south-east part of the platform on the boundary with Pre-Urals foredeep, the karst is developed in the arches and on the limbs of tectonic swells. In the Ufa swell arch manifested in the relief in the form of plateau there are karsted flat-pitching Artinskian and partially Kungurian limestones and dolomites. The plateau is karstic waters catchment area. Along its margins there flow out karstic springs.
The western and eastern limbs and the northern plunge of the Ufa-swell are composed of gypsums, anhydrites, limestones and dolomites of Iren horizon of the Kungurian stage of the lower series of the Perm system. To the north these deposits are spread in the arch of the Krasnokamsk-Polazna swell. Upon all this area, karstic breccia is found. The karstic forms are represented with numerous sinkholes, basins, karstic ravines and karstic lakes. In the Kungur area there is situated Kungur ice cave (5.6 km).
The Solikamsk and the southern part of the Pechora tectonic basin of the Pre-Urals foredeep are characterized with karst in the salts of Kungurian stage. In place of salts lea ching there have been formed considerable in area closed lows with great thickness of loose Quaternary deposits. Saline springs open onto the surface.
In the Urals folded belt there are karsted mainly the limestones and dolomites of the Devonian, Carboniferous, Permian, to a lesser degree Ordovician and Silurian system.
The karsting rocks occur in the form of anticline and syncli ne folds accompanied with fracture dislocations. Typical are sinkholes, basins, lost rivers, springs, caves and flind creeks.
TYPES OF TECHNOGENIC EFFECTS ON THE ECOLOGICAL MEDIUM OF'KARST AREAS
Perm Region bears a considerable technogenic load. The area distribution of various types of technogenic effects on the environment is conditioned by presence of commercial minerals, timber and water resources, the geographic position of the region on the border of the western and eastern areas of the country, the history of its developing. The greatest changes of the geological medium of the karst areas are caused as a result of various types of the human economic activity, such as: 1) mining industry (Kizel Coal Basin,Verkhne kamskoye Potash Salts Deposit, Volgo-Urals Oil and Gas Bearing Area); 2) hydrotechnical construction (Kamskaya hydroelectric station and Kamskoye Reservoir); 3) urban and industrial construction (on the basis of commercial minerals, timber and water resources in Perm Region there appeared large industrial centers - cities of Perm, Berezniki, Kizel, Chusovoy and others); 4) communication and transport constructions (the region is crossed by railway and highway lines, electric transmission lines, oil and gas pipelines); 5) water distribution systems (use of fresh drinking, medicinal and commercial mineral waters); 6) timber industry and agicultural activities (tree felling, agriculture chimization).
All these kinds of the human economic activities change some or other components of the environment (overlaying deposits and karsting rocks, relief, underground and surface waters, atmosphere, biosphere) which is reflected directly or indirectly on the basic conditions and growth factors of karst and causes its activizatio or damping (Gorbunova,1979).
TECHNOGENIC CHANGES OF KARSTING ROCKS AND OVERLAYING DEPOSITS
In many construction types, driving mines, commercial minerals and construction materials extraction (especially gypsum and limestone) the soil cover is distributed, the blanket deposits are removed partially or entirely, the karsting rocks are exposed. In some cases, technogenic overplaced soils are used in construction forming media aggressive to karsting rocks. In other cases, the entries spoil heaps consist of soluble minerals. The constructions being erected and their use create static (industrial and civil objects, reservoirs) and dynamic loads (blasthole drilling, intensive transport traffic).
The consequence of these types of economic activity is change of the stressed condition of karsting rocks, their fracturing, formation of technogenic landscape, appearence of' concentrated absorption centers of atmospheric precipitation and karstic waters recharge.
The activization of karst caused by the disturbance of the cover and redistribution of the surface run-off was observed in the area of the main gas pipelines Siberia-Center-West. They cross the western limb of the Ufa swell to the south of the city of Kungur where are karsted gypsums and anhydrites, to a lesser degree the limestones and dolomites of the Kungurian stage. There can be traced a connection of the karst and the river netwotk with tectonic disloca tions. Most karsted are the sites where the gypsums are exposed and covered with soil vegetable layer or eluvium of small thickness. The number of sinkholes for 1 ha here reaches 95, the total area of the sinkholes makes up to 50 per cent of the site area, the average conventional surface reduction at the expense of the sinkholes (to denudation) equals 57 cm. The initial size of the collapse sinks is 2 to 3 m, the average diameter of the sinkholes formed is 7 to 8 m. From May 1983 to October 1984 in the gas pipeline area of 40 m wide and 5.4 km long there appeared 24 collapse sinks, and in 1985 their number exceeded 45. A great part of the collapse sinks had diameter of no more than 2.5 m, depth of 2 m and only in some cases 5 m.
For the pipelines used in construction such collapse sinks presented no danger, but further activization of col lapse sink forming may have negative sequences. To provide, safety of construction and exploiting of gas pipelines anti karst measures were recommended: filling the karst sinks with non-draining material, arranging of the surface waters run-off, reduction of transport load stoppage of blasting operations in the pipeline area. The condition of the constructions is. being watched.
Intensity of the sinking process incerases after construction of industrial and civil objects and roads, the sinking sizes being increased. For example, from 1960 to 1971 im Kungur region in road-side ditches and reserves there appeared 22 collapse sinks (Lukin,Yezhov, 1975).
In quarring of limestones and gypsum the overlaying deposits are removed. Blasting operations in quarries lead to fracture forming and opening in the rocks which promotes infiltration of atmospheric precipitation. The suffosion and dissolution activization causes numerous suffosion-karstic collapse sinks, for example, in the vicinity of the gypsum quarry Yergach to the north-west of Kungur.
TECHNOGENIC EFFECTS ON UNDERGROUND WATERS OF KARSTING MASSIFS
The karst activization is caused by change of the level regime and chemical composition of the karstic waters in the water intake areas, in mine and quarry outfall and systematic drainage. In these cases there form depressional sinkholes, the hydrodynamic zones are shifted, the karstic waters direction changes and the velosity increases.
In Kizel Coal Basin the coal-bearing strata of the visean stage of the Lower Carboniferous series occurs under the karsted carbonate rocks. Some mines passed through cavities and caves filled with water. In the karst influence zone, the. mine water inflow reach 2,000 to 2,500 m3/h. As a result of the karst waters drainage there develop depressional sinkholes, and thick strata of carbonate rocks are involved in the active water exchange and karsting zone. In interaction with sulfur-containing coal-bearing rocks, the bicarbonate karstic waters are transformed into bisulphate waters enriched with ferrum, aluminium and other microcomponents. The mine waters run down into rivers and are partially absorbed by ponors. Moving along karst channels in carbonate rocks the bisulphate (pH 3 to 4) polluted mine waters are partially neutralized and cleaned. In the southern part of the basin the mine waters are released into the river Gluhkaya (Problems……, 1988) which disappears in the cave and flows for 7 km by underground route. The river feeds a spring in the valley of the river Chusovaya whose freshet debit reaches 10 thousand m3/h. After the mine waters passing through the underground karst channels the ferrum, aluminium and sulphate concentration reduces ten and hundreds of time. At the same time there occurs contamination of stalactites and stalagmites in caves with ferrum hydroxides. Some cavities when filled with sediments disappear.
Feeding, motion and outflow conditions and the chemical composition of karstic waters change considerably in the influence zones of hydroelectric stations and reservoirs. Near Perm, on the river Kama, there was constructed Kamskaya Hydro in 1954 (Mamenko, 1967). At the storage dam basement, under argillites, sandstones, gypsum limestones and dolomites of the Ufimian stage to which water-bearing horizons are confined, there occur gypsums and anhydrites of the Kungurian stage which are regional waterproofs. After filling the reservoir there was intensified filtration at the storage dam basement. In some sites there was observed desalting of the underground waters, in others there appeared sulphate waters which pointed to dissolution of gypsum. In this situation, consolidation of the existing cement shield was done with a chemical gelforming silicate solution (Maximovich N., Sergeev, 1983). The injection consolidation and post-injection processes provided gypsum protection against dissolution and increased the storage dam stability.
Filling the Kamskoye reservoir raised the water level by 20 to 22 m. Its banks within the limits of the Krasnokamsk-Polazna swell are laid with gypsums and anhydrite of the Kungurian stage. Part of the caves was flooded. In the waves impact zone there formed leaching recesses and new small caves. Introduction of the river waters into the karsting rocks, seasonal fluctuations of the water level in the coast area reaching 7 to 8 m, caused activization of suffosion, evacuation of material from the filled karst cavities, gypsum dissolution and collapse sink forming. In the reservoir influence zone on the territory of the settlement Polazna, from 1956 to 1961 there occured 11 collapse sinks while for the previous 50 years there were only two (Lukin et al.,1963).
The karst activization both in the upper and deep horizons is observed in connection with drilling operations for oil, gas and salt as well as developing of oil and potash salts deposits in the same areas. The boreholes being imperfect by construction promote vertical flow exchange and mixing of mineralized and fresh waters which increases the waters aggressiveness towards the karsting rock. Some abandoned wells gush polluting the rivers. At present there are developed and introduced well constructions providing the aquifer isolation.
About 50 percent of oil resources is confined to fractural kars reservoirs. Developing a greater part of deposits is done maintaining the formational pressure by fresh water injection into off-contour wells which activizes the dissolution processes of carbonate and sulphate salts in deep horizons. The processes are promoted by activity of sulphate-reducing bacteria. To intensify the oil inflow, the hydrochloric acid is injected into the seam (up to 100 m3 and more) at the concentration of 10 to 20%. As a result of the carbonate rocks dissolution in the near-face part of the well, the volume of the fractural karst reservoirs and the oil inflows increase. As noted by I.N.Shestov et al. (Problems... ,1988), an active impact on karsting rocks of the oil development wells spreads over to the depths of hundreds of meters.
COMPLEX CHARACTER OF TECHNOGENIC IMPACT ON THE ENVIRONMENT IN KARST AREAS
In territories of considerable technogenic load there considerably change the conditions and factors of karst formation due to irreversible transformations of the landscape o and the rocks, pollution of surface and underground waters, atmosphere and atmospheric precipitation, degradation of vegetation.
An example is Verchnekamsky industrial complex including, besides potash salts enterprises of the city, settlements, large water intakes, linear (engineering) constructions, timber processing and oil industries (Ziling,1983). The salt extraction has been taking place there for more than 500 years. The salt stratum of the Kungurian stage (underlying rock salt, potash salt, overlying rock salt) and the intermediate stratum are overlied with clays, limestones, gypsums, marls, sandstones of the Ufimian stage and Quaternary deposits to which aquifers are confined. In chamber working of potash salts artificial cavities are formed, redistribution of stresses in the rocks takes place, opening of fractures in the overlying rocks, slow sinking of the surface. According to G.V. Beityukov (Problems..., 1988), in driving and developing all the mine shafts in fractural zones there are noted water shows. In the overlying rock salt and in the carnallite rock in some places there were uncovered karst cavities of hundreds of cubic meters in volume. In July 1986 in one of the sites there occured a collapse sink. It had the size of 40 by 80 m in the plan with the depth of 25 m to the water level. The collapse was accompanied by al gas explosion and light effect.
In worked-out entries there condenses moisture in the form of small pools or drip from the roof. In some sites it dissolves the salt, in others there deposit stalactites and sinter salt crusts from oversaturated brines. The salt leaching zones formation had been promoting by, in the past, brine extraction from more than 200 wells of salt industry. Some abandoned wells have turned into "artificial" springs. In drilling wells of the former salt fields there were uncovered karst cavities in the salt strata.
The salt was of potash salts industry occupy an area of more than 700 ha. Every year they increase by several millions of tons. The spoil heaps and industrial liquid wast receivers pollute the environment by salinization and create a lifeless technogenic landscape. In salt spoil heaps there develops a peculiar "technogenic" karst under the effect of atmospheric precipitation and temporary surface run-off: numerous ponors, karren, small sinkholes, channels and caves.
Various kinds of the human economic activities called technogenic impact change karstic processes course. These changes have various trends. In most cases the technogenic impact lead to activization of karstic processes as a result of the environment components deformation (rocks, hydrosphere, atmosphere, biosphere) which determine the basic conditions and factors of karst formation. The karst activization has a negative impact on engineering geological constructions and may cause hazardous situations. It shows itself not only in upper but in much deeper horizons of the rocks. Slowing or damping of the karst process is a result of some or other engineering geological measures connected with construction on karsted rocks. The environmental response to the technogenic impact depends on the karst type: saline, sulphate, carbonate. As a result of mining activities on the surface there are accumulate soluble technogenic soils which show "technogenic karst". Evacuation of dissolved components from the soils pollute the environemnt. The human economic activities being planned in karst areas must be based on the predictions of the karstic process development in view of the environmental changes under the influence of the existing and designing units and provide for nature protection measures.
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