Influence of the Romanian lignite deposit exploitation on the environment

Category Mine
Group GSI.IR
Location 20th WORLD MINING CONGRESS 2005
Author Dumitru Fodor* - Maria Lazar- Vasile Pop
Holding Date 15 January 2006

ABSTRACT

 
Among the coal deposits mined out in order to obtain electrical and thermal power, the lignite deposit of Oltenia zone is worth mentioning. Taking into consideration the lignite deposit mining which is carried out by large scale open casts, the influence of such operations on the environment is to be assessed. The paper deals with the main results of the assessment of the environmental impact as well as with the causes and consequences of this impact related to both the environment and the individuals. For the five mining basins of Oltenia zone, the land surface areas taken out of the economic use have been assessed in order to open and mine out the deposit and to build the waste dumps.
Key words: mining exploitation, coal, impact, environment, ecological reconstruction.
 
 

INTRODUCTION
 
In Romania there are more than 3.1 billion tones of coal industrial reserves, of which more than 2.3 billion tones are lignite reserves. The Romanian lignite deposits are spread over three distinct zones as follows:
·       Zone I, in the sub-Carpathian depression of Getic Plateau, is situated between Olt river and Danube and it contains the largest reserves in the country;
·       Zone II, in the pre-Carpathian depression between Olt and Buzau rivers includes the lignite deposits of Câmpulung, ھotânga, Filipe؛tii de Pمdure and Ceptura. Additionally, there are the mining basins of Eastern Carpathians: Baraolt – Vârghi؛ (lignite) and Comane؛ti - Bacمu (brown coal);

·      
Zone III, situated in the panonian depression to the North-Wets of Transylvania and includes brown coal and lignite deposits from Sمrma؛ag, Voevozi, Surduc and Borod.

                                               
Rovinari, Motru, Jilt, Albeni–Seciuri, Cerna-Cerni؛oara, Berbe؛ti-Alunu and Husnicioara basins are located within Zone I and it also hosts more than 90% of the total lignite reserves, which are mostly mined out by open cast (figure 1).
 
The lignite production of Romania contributes by approximately 35-38% to the electric power production and by 20% to the country thermal production.
 
In all Romanian basins the mine able lignite layers thickness ranges between 1.0-8.0 m and occur as some layer packages with waste intercalations and both the floor and the roof contain either free level or under pressure water aquifer formations and it results in additional difficulties and expenses at the opening, preparation and mining operation completion due to the works required. The Romanian lignite deposits are
located within regions where the youngest geological formations are prevailing (Dacian, Levantines, Quaternary) consisting of soft cohesive and non-cohesive rocks such as marnes, clays and sands.
 
In the 18 open casts of Oltenia continuous technological flow-sheet is applied to a large extent (with an approximately. 92% weight) and it consists of rotor excavator use combined with the high capacity belt conveyors and waste dumping machines. The great number of open casts of the area as well as the technologies applied for coal extraction provides a negative impact on the environment, respectively air, soil and waters. As a result, of the coal production increase and importance within Romanian National economy, the coal mining sector in general and the open casts in particular, extend over large surface areas required to locate the exploitation perimeters, the mine yards, access roads, waste dumps, etc.
 
Depending on the mine location, significant farming, meadow, graze, forest, orchards land areas are to be taken out from either the forestry or other usage circuit. The lands where the waste dumps have been placed totalize thousands and tens of thousands hectares, which are taken out of their current usage. It is considered that in the areas adjoining the open cast fields, areas that are completely destroyed due to the stripping and extraction operation completion, the surface areas impacted is four up to ten times larger. They are required for the construction of access roads, site organization, waste dump construction etc. Due to excavations performed on the neighboring lands, the bio-diversity has been destroyed, the underground water regime has been modified as well as the natural geo-chemistry of the soils and the erosion process is strong; further to such works, „moon landscape are left behind” and „ industrial deserts”.
 
IMPACT OF MINING OPERATIONS ON SOIL
 
For the coal sector of the mining industry, the soil pollution is the most significant ecological damage and it is particularly obvious in the lignite mining.
The impact on soil mainly consists of:
·  Medium and long term land occupancy;

· 
Subsidence event occurrence;

·  Impacting localities due to the individual properties, technical-economic construction, roads, power lines, churches, etc., resettlement.
 
SOIL DEGRADATION AND OCCUPANCY
 
It is estimated that the surface areas to be impacted by the Romanian mining will cover approximately 1 % of the farming surface area of the country. A particular case is represented by Rovinari, Motru and Jil‏ basins of Olt from Gorj Country where the total surface area damaged by the open cast operations is more than 35,000 ha, that is 18% of the county farming surface area.
 
Although up to present, there were no accurate statistics either worldwide or at National level regarding the land occupancy by mining projects, it can be said that more and more surface areas are taken out of the economic usage due to the extension of the open cast operations but, nevertheless they are smaller than those required for the industrial or transport installations.
 
Once the working was started and moved from the open casts, the fields and afforested hills disappear while the dumps initially cause a total degradation of the landscape.
 
On the whole, the coal mining developed within Oltenia basin approximately 2,000 ha were given back the farming or forestry usage, of the total 17,000 total hectares of impacted lands and the rest is to be arranged and returned to the economic entities owners in the near future. 80% of the impacted areas consist of farming lands while only 20% consist of forests. The actual amount of lands for the 18 large scale open casts of Oltenia basin is 31 ha for one million tones of mined out lignite.
 
Another form indicating the impact of the open cast and underground operations on the environment consist of surface land occupancy and their temporary or longer period taking out of the economic usage as  result of the storage of material produced at the waste stripping, mining works excavation and from the selection – sorting installations for coal.
 
The main damages caused by the waste dumps on the environment consist of:
·  Visual unpleasant view , destruction and large surface area
·  occupancy; surface and underground water pollution with chemicals dissolved or solid particle suspensions engaged from the dumps by the rainfalls or infiltrations ;
·  Pollution of air due to the gas resulting at waste dump containing minerals or oxidation products and their burning;
·  Material disasters and human life risks due to their stability etc.
Also, further to the waste dump location, the land configuration much changed in the sense that new relief heights of 15-20m and 90-100m occurred in the meadow areas (figure 2).
 
The surface areas where social – municipal constructions, transport ways or new river beds (about 25%) are located are removed from the economic usage. The other surface areas occupied by the lignite exploitations of Oltenia basin are temporarily removed from the economic usage and later on they are re-arranged in accord with their new usage established by the interested parties.
 
In accordance with the Romanian environmental legislation, the surface areas impacted by the lignite open cast operations are rehabilitated from ecological point of view. The dynamics of these surface area occupancy and rehabilitation is described in table 1.
 
Specification
2006
2007
2008
2009
2010
Newly occupied surface
 
325
 
315
 
300
 
300
 
270
Rehabilitated surface
 
795
 
790
 
801
 
1400
 
1400
 
Table 1: Dynamics of the surface areas 2006 – 2010
 
SUBSIDENCE
 
The underground lignite mines have a significant impact on the surface, the constructions and installations located in the said areas, depending on the work depth and mining method used.
 
The deformations occurring (cracks, land slides, subsidence) have an impact on the  built up areas, the pipelines of any type, cables, roads, , high voltage lines, railways, hydrotechnical constructions, fertile soil and at the same time on the normal growth of the flora and activities in the area. Besides, the presence of such deformations results in a sad landscape.
 
The subsidence occurrence is usually a slow process, but there is known also some sudden caving of the land surfaces. In both cases, subsidence depressions are formed and sometimes they have significant impact on the civil and industrial constructions. Once the subsidence process has started, the induced subsidence is difficult to be stopped. Usually, the subsidence process continues until reaching an equilibrium condition and it is an irreversible process, the deformation of the land surface is permanent. In the depressions thus created, waters are accumulated either by flooding or by taking over some natural streams (streams, rivers), or by direct rainfall water accumulations.
 
The main causes of the induced subsidence are:
·  Exploitation of some fluids and underground gases;
·  Completion of some large water collection facilities;
·  Useful mineral underground mining.
 
Thus, the subsidence- settling processes are particularly noticed in case of thermal power stations located at the central part of coal open cast areas. Rogojelu thermal power station is located n the lower terrace of Jiu river which is approximately 13 m thick and the host rock consist of clays and Pliocene marne alternations of about 14.5 m, overlying a coal layer and an under pressure aquifer layer underlying it.. The underground water level decrease led to the modification of the tensions existing in the field, in the sense that such tensions increased and determined the settling of rocks and implicitly the subsidence occurrence. The time process evolution is monitored by means of topographic measurements performed on the thermal power station platform. The settling process due to the aquifer fine grain layer dewatering and consolidation is not expected to be more than 10 up to 20 cm thick at the central part of the settling area. The settling process will decrease accordingly as the dewatered area is farther.
 
The coal exploitation from Oltenia open casts requires the descent of the water levels of underground waters by more than 50-100m, and determines the occurrence of rock settling and subsidence process which may impact the slopes and hillsides from around as well as the constructions located within the impact area.
 
Further to dewatering works performed since 1990 in Rovinari basin, the hydrostatic level of the water decreased and it impacted the water supply to the villages neighboring the open casts. About 90 million m 3 of water resulted at dewatering drillings and open cast pump stations, are discharged from this basin open casts.
 
In most cases, the designs of some useful mineral mining operations do not consider the value of drinking water reserves existing within the future mining fields, the deposit dewatering being mentioned only as technical measure to protect the mining works against water infiltration. Besides the effective loss of drinking water reserves, the dewatering process of mineral deposits disturb the entire hydrographic regime of the area and it results in a negative impact on the surface fauna and flora.
 
The subsidence caused by the underground mines is indicated by the occurrence of some subsidence events of different sizes and by the risks the constructions in the area are facing. The mining subsidence occurs in all rock types and the underground voids create the conditions generating such events. The exception consists of small voids located at large depth in compact rocks.
 
The efforts around the underground voids are redistributed determining the occurrence of a closure trend due to the rock movement to the inner part. This dynamics is transmitted to the surface by loosening, settling and caving of rocks situated above the void. There results the formation of some caving beds of subsidence of even of caving cones. In the zones close to the initial subsidence there occur other cracks and dishevelment indicating the extension of the subsidence process. The mining subsidence is differently indicated depending on the deposit features related to layer thickness and inclination, rock physical and mechanic properties, tectonics and local hydro-geology and, of course, the adopted mining technologies. The land surface deformation is a complex process and it is identified by the subsidence bed depth (vertical movement) inclination and horizontal movement (towards the inner part of the subsidence bed).
 
As a result of the underground technological processes, horizontal extension deformation and vertical breaking deformation are sent to the surface and thus, subsidence process occurs forming sometimes, large extension beds.

The vertical deformations determined by the lignite underground mining vary between 100-3,500mm and sometimes, there were noticed spectacular subsidence of 5 - 6 m (figure 3).

 
RESETTLEMENTS
 
Until the time of the lignite reserves of Oltenia basin depletion, 56 localities were impacted and 24 of them were entirely impacted. There have been resettled 2,200 individual properties, 40 social-municipal constructions, 5 churches and 6 churchyards so far. For thee population from the impacted localities, the mining companies constructed new houses situated on new sites agreed with the territorial administration representatives and located outside the open cast impact area. Also, there were reconstructed the churches in the new localities using fragments, sculptures, paintings, crosses, altars etc. in order to preserve at the extent to which it is possible, the local particularities.
 
MINE EXPLOITATION IMPACT ON WATERS
 
The open cast operations results in a smaller impact on underground water quality, but they have a significant impact on the hydrostatic level. In case of lignite deposits, the hydro-geology influences the applied mining technologies both in case of underground and open cast operations. Prior to opening the mining fields, there were carried out investigation works of the aquifer horizons and the hydro-geological parameters, the dewatering technical methods and the hydrotechnical works were determined to allow the exploitation of the lignite layers under maximum safety. Thus, taking into account the hydro-geological characteristics of the region and the requirements of the mining activity, different methods and dewatering techniques were used as well as the dewatering large diameter drill hole equipped with submerging pumps, dewatering trenches and galleries.
 
The completion of the dewatering works in the mining fields and open casts aims at:
·       Dewatering the aquifer layers situated in the coal layer roof;
·       Taking over the underground water flows from the perimeters outside the mining fields;
·       Removing the stresses on artesian horizons situated in the mine able deepest coal layer of the perimeter;
·       Increase of the slopes stability of the opening trenches, of the benches and waste dumps as well as of the open pit margins;
·       Prevention of the suffusion and slope slide events;
·       Prevention of the open cast flooding by the eruption of water from the artesian horizons situated beneath the open cast floor.
 
The impact of the dewatering works completed in the mining fields from Oltenia area and refers to:
·       Modification of the hydro-geographic regime by extending the mine able perimeters and dewatering drill holes;
·       Modification of the pressure, aquifer horizon levels and flow-rates as a result of the dewatering works performed at surface and in underground;
·       Modification of the surface water quality due to the mine water, rainfall and residual waters discharge in the emissary.
 
The following water amounts are discharged annually in the emissary from the Oltenia lignite open casts:
·       4 millions m3 mine waters;
·       86 millions m3 open cast water;
·       4 millions m3 dewatering drill hole water;
·       1 million m3 sewage waters.
 
The discharge of waters outside the open cast perimeter is carried out through metal pipeline. The water must be directed as far as possible from the open cast perimeter so that it does not form infiltrations and it does not go back in the open cast. The metal pipes are so sized that they can take over the maximum flow-rates generated by the pump stations. The discharge pipes which remain at the same location for a longer period will be buried so that it did not jeopardize the open cast operation development or it did not freeze during winter times. The pipes which are not buried when they are not in operation during winter when the temperature are below 0°, they will be emptied. To do this, the pipes will be inclined so that water flows dowse and with emptying valves.
 
The above mentioned indicate that the lignite open cast mining and the completion of dewatering works influence the underground water regime and there is a qualitative and quantitative impact on these waters.
 
The qualitative impact develop dint:
·       the dewatering of the ferric aquifer layers both from the open cast perimeter and outside them;
·       destruction of the aquifer formations in the excavated perimeters;
·       diminution or even elimination of some underground water resources resulting in the well and diminution of water catchments flow rates;
·       modification of the underground flow regime by increasing the filtering velocity and reduction of flow-rates within the extension areas of the depression cones occurred as a result of the drainage system operation;
·       modification of the erosion process dynamics influencing the overall hydric balance-sheet of the basin.
 
For instance, it has to be said that, due to the ferric cloth lowering as a result of the dewatering works performed in Rosia de Jiu open cast, the water level in the wells was lowered over a distance of 5 km and sometimes water disappeared completely from the wells of the neighboring localities. The worst situation was indicated in Rovinari town and in Moi, Timi؛eni, Fمrcم؛e؛ti, Bâlteni, Vlمduleni localities and Rovinari platform.
 
To ensure the water supply to the above localities, the coal mine completed water wells at their own expense and these wells are water supplied from the artesian horizon and the required pipelines, but their running was not always as expected and the quality of the water changed as the underground chemistry modified.


The dewatering operations of the aquifer layers led to the diminution of underground water sources due to its drainage and discharge. The annual discharge rate of more than ten million cubic meters according to the measurements of the flow-rates from Rosia de Jiu open cast pump stations is a sure thing. The diminution of the underground water resources from the zones adjoining Rosia de Jiu open cast ranges between 5.0 millions m3 for the artesian horizon which is subject to stress elimination to more than 10 millions m3, for the ferric horizon.

 
The impact on the surface water quality is indicated by:
·       increase of the pollution risk of all aquifer layers, particularly of the ferric ones;
·       modification of the underground water chemical composition due to the infiltration of different substances and slimes.
 
The studies and systematic remarks led to the conclusion that due to the depositions along the route and natural purifying process in the lower areas of the rivers, the quality of waters complies with the requirements of category I for most of the mining basins. Table 2 presents the quality of used waters from the main coal mining basins of Oltenia in comparison with the maximum admissible concentrations of the standards in force.
 
To reduce the impact of the open cast dewatering on the adjoining areas, it is expected: to
·       monitor the dewatering works and the underground water level by means of drillings in the adjoining areas;
·       adoption of some new efficient methods meant to watch the aquifer formation shielding by means of some filtering proof dams, located on the open cast contour;
·       monitoring the deformations events though topographic marks allowing the signal analysis regarding the deformation evolution.
 
The remarks and the studies performed within Oltenia mining area led to the conclusion that the mine water and open cast water discharge containing suspensions has no impact on Jiu river water quality.. However, to reduce the amounts of suspensions discharged in the main water courses of the area in the future, there will be constructed mine water retention and sedimentation basins. Also, in future, particular efforts will be made to use the underground water discharged further to mining operations, for industrial and irrigation purposes.
 
Both the open casts and the constructions and installations corresponding to the mining yards often require significant hydrographic changes in the area, by diverting some water courses or the completion of some particular hydrotechnical works. Thus, in Oltenia zone, the diverting of Jiu, Tismana, Jales, Motru, Oltet rivers and of some smaller tributaries over distances between 5 and 40 km, as well as the construction of retention and mitigation dams including the auxiliary works required. It is considered that although the respective water courses were diverted, the hydrotechnique works were profitable for the area as 8,000 ha of land were no longer flooded.
 
IMPACT OF MINING OPERATIONS
 ON THE AIR
 
The mining industry either directly by the mining operations themselves or indirectly by the useful mineral storage-processing and treatment installations generate polluting elements impacting the air.
 
The air pollution in the mining areas which deal with lignite and brown coal extraction is less intensive while among the pollution sources it is worth mentioning:
·       air poisoned discharged from the underground containing much technological dust and different gases released by the layers, internal combustion engines, oxidation processes and underground fires etc.;
·       own thermal power stations of the mines used for heating the administration buildings and production of hot water for bathrooms;
·       waste dumps both due to the dumps and current sloping operations and the gases and smoke released from their combustion areas;
·       dust resulted at the technological transport of waste and coal by ropeways, belt-conveyors, trucks or rail cares in the mine yards, processing plants, coal storage areas waste dumps;
·       dust resulting at the shifting locations of the transport system both for waste and useful minerals. Most often there are locations in the open c\casts where continuous belt-conveyor transport system is used.
 
The air pollution determined by the dust release, particularly due to the truck and belt conveyor transport operations is a major problem for the localities neighboring the mining area. The Romanian standard value of the air quality related to the dust content is 0,5 mg/m3 and it is up to ten times higher in the neighborhood of coal storage areas, along the roads connecting the mines to the waste dumps and on the belt lines.. The dust generated because of the wind erosion action on the dry surface of dumps or mines where little vegetation exists cause also problems. The most severe impact was noticed at Fمrcم؛e؛ti, Timi؛eni, Mمtمsari, Mمnمstirea and Motru.
 
In general, the direction of prevailing winds blowing in the area is considered when designing the open casts and working face advances. To reduce the air pollution in the area and the noise pollution around the open cast, protection shields made of trees are provided. To this aim, prior to start the stripping operations, the trees from the mining field are taken out, but their roots remain in a soil coat and then they are replanted to form the protection shields. The protection shields act like a brake in front of winds reducing the dust and noise amount in the area. The diminution of the dust released in the air can be done by providing ballasting the industrial roads of the mining basin and thus the dust amounts are reduced.
 
In case of lignite and brown coal underground mining, the air damaging is actually inexistent as the dust concentration in the mine air is eliminated due to the self-treatment by condensation process on the aeration work support; in general it does not exceed the admissible values for industrial aeration. In exchange, the open casts themselves and the waste dumps can provide air impurifying particularly during the dry seasons and during the strong winds season. The waste dumps, due to the fire burning sometimes for years, have also a negative impact on the environment.
 
The processing plants constitute also a source of air dust pollution while the thermal power stations discharge in the air high amounts of sulphur as sulphur dioxide which is considered the most dangerous pollution matter for the air quality. Almost half of the SO2  amounts result further to coal burning in the power stations.
 
Table 3 presents the air quality of Motru and Rovinari basins compared to the maximum admissible values in force in Romania.
 
Polluting matter
Maximum daily admissible conc. [mg/m3]
Mining basins
Motru
Rovinari
Ammonia
0,1
0,015-0,042
0,014-0,051
Nitrogen Dioxide
0,1
0,005-0,019
0,015-0,038
Sulphur Dioxide
0,25
0,001-0,008
0,005-0,013
Sedimentary powders
17 g/m2 month
13,7
93,04
 
Table 3: Air quality within some of Oltenia mining areas
As for the powder concentrations, the measurements indicate values that comply with the sanitary norms in force for protected areas (urban and rural localities), but they are higher than the normal admissible values for the working places and near the technological installations. Rogojelu thermal power station area constitutes a particular case because the coal storage and management areas of the main open casts of Rovinari basin are located there.
 
The forest tree cutting, the destruction of gardens, demolition and resettlement of villages from the open cast areas reduce to minimum values or even cancel the climate, hydro-geological and protection against erosion functions of the vegetation..
 
The destruction of vegetation around the mines and open casts damage the natural balance between the environmental soil-air-water factors and modifications occur and they are always negative for the environment. For instance, in the Oltenia open cast area, climate modifications were noticed in 1931 -1960 consisting of:
·       increase of the temperature of the environmental factors both during the cold and hot seasons and the green house effect occurred, too;
·       increase of the relative humidity of the air;
·       increase of the duration of sun shining;
·       more intense rainfalls;
·       increase of the number of foggy days;
·       increase of the number of snow areas.
 
NOISE POLLUTION
 
The Noise produced by the mining equipments and installations often disturb the environment. The noise sources in the open casts with continuous flow-sheet are the driving reducers of the technological equipments. In Oltenia open casts there were performed noise measurements and noise assessment (table 4) on three levels:
·       source noise measured at 10-20 m from the source;
·       noise of a close field measured at several tens of meters from the source;
·       noise of a remote field measured at several hundreds of meters from the source.
 
Equipment
Measuring distance
Noise release
SchRs 1400 excavators
30-50 m
80 dB
SchRs 1400 excavator
Mechanical cab
84 dB
Belt conveyor
10 m
78 dB
Belt conveyor
Sat Mمtمsari (50 m)
75 dB
Dumping equipment
50 m
77 dB
Table 4: Noise release measurements
 
The noise release from the belt conveyors and the vehicles transporting the mined out material through the villages from the adjoining areas reached 75-80 dB, exceeding the recommended value of 55 dB even at remote distances from the source producing a discomfort to the local people.. The rehabilitation and maintenance of the belt lines may result in the diminution of noise intensity, but it cannot eliminate it completely. Also, the admissible noise release value in the equipment canopy was exceeded and thus the operators were exposed to vibrations impacting their health.
 
CONCLUSIONS
 
To determine the impact of the lignite operations developed in Oltenia basin, there were carried out measurements, assessments and remarks referring to most of the mining perimeters of the area, and the results were processed, interpreted and presented in the present paper.
The most important lignite deposit of Romania is located within Oltenia area and the exploitation is developed both in open casts or underground mines. The 18 large open casts running in the area have an impact on all environment factors mainly due to the occupancy of large surface areas of land which have to be removed from their economic usage. The resettlement of the localities from the mining areas, diverting the communication ways and water courses are activities with significant environmental, social and economic impact. The dewatering of the aquifer formations for safety mining the lignite deposit determined, on one hand, a hydro-dynamic unbalance within the impacted areas (leading both to the underground water resource diminution and to the subsidence and settling of the adjoining areas), and on the other hand, the modification of the water chemistry and increase of the solid suspension content. The air contamination, micro-climate modifications and excess of admissible values for noise represent other impacting elements of the mining operations on the environment of Oltenia region. The underground lignite mining has an impact on the environment at a lesser extent than the open casts, the major issue being the subsidence process occurring in several areas taking into account the subsidence of more than 5 m depth.
 
REFERENCES
 
1.     Fodor, D., Baican, G., 2001, Impact of mining industry on the environment: Ed. Infomin Deva.
 
2.     Fodor, D., Baican, G. s.a., 1999, Coal Mining in Romania at the Beginning of the 21st Century: Revista Minelor, No. 10-11.
 
3.     Lazar, M., 2001, Ecological rehabilitation: Ed. Universitas Petrosani.
 

 

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