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Paper: Possibilities of oil shale mining under the Selisoo mire of the Estonian oil shale deposit


txt: See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/236005585 Possibilities of oil shale mining under the Selisoo mire of the Estonia oil shale deposit Article in Environmental Earth Sciences · December 2013 DOI: 10.1007/s12665-013-2396-x CITATIONS 17 READS 98 5 authors, including: Some of the authors of this publication are also working on these related projects: Rikastamine View project Vivika Väizene Tallinn University of Technology 91 PUBLICATIONS 250 CITATIONS SEE PROFILE Juri-Rivaldo Pastarus Tallinn University of Technology 36 PUBLICATIONS 61 CITATIONS SEE PROFILE Ylo also Ülo also in Russian Юло Joann Systr… Tallinn University of Technology 15 PUBLICATIONS 45 CITATIONS SEE PROFILE Ingo Valgma Tallinn University of Technology 404 PUBLICATIONS 1,503 CITATIONS SEE PROFILE All content following this page was uploaded by Ingo Valgma on 11 March 2015. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. Look Inside Get Access Find out how to access preview­only content Environmental Earth Sciences December 2013, Volume 70, Issue 7, pp 3311­3321 Date: 27 Mar 2013 Possibilities of oil shale mining under the Selisoo mire of the Estonia oil shale deposit Abstract The paper presents results of the study on oil shale mining (Estonia underground mine) possibilities under the Selisoo mire. The Selisoo area is 2,051 ha in extent, and most of the mire is in natural state. Peat layer consists of thick (4.4–6.5 m) oligotrophic peat. Mining under Selisoo will go at depths 65– 70 m under the surface. The mining field of the Estonia mine was planned between Ahtme and Viivikonna fault zones. The lowest hydraulic conductivity of carbonate rocks 0.11 l/day per m2 is found in the Oandu layer and for peat it is 0.35–0.0002 m/day. Therefore, together they form a good aquitard. When the annual rainfall amount is the highest, the difference between horizontal water inflow and runoff is positive with 127,000 m3 . Positive water balance is guaranteed in case of precipitation being at least 540 mm/year. The positive water balance is important for preserving the ecological system of Selisoo mire. For guaranteeing long­term stability of mine pillars, a new calculation method has been elaborated, based on the conventional calculation scheme, where the factor of safety is more than 2.3. Rheological processes are out of question, collapse of the pillars is impossible. Stability of the underground constructions and overburden rocks must be “eternal”. The criteria were elaborated for oil shale mining and will guarantee preservation of mires in natural or close to natural state. Article Metrics Citations 5 Social Shares References (52) 1. Botch MS, Masing VV (1979) Ecosystems of USSR. Nauka, Leningrad. [in Russian] 2. Fetter CW (1994) Applied hydrogeology, 3rd edn. Macmillan College Publishing Company, Inc, New York, Library of Congress Cataloging­in­Publication Data, pp 1– 691 3. Hints L (1997) Aseri Stage Lasnamägi Stage Uhaku Stage Kukruse Stage Haljala Stage. In: Raukas A, Teedumäe A (eds) Geology and mineral resources of Estonia. Estonian Academy Publishers, Tallinn, pp 66–72 4. Hints L, Meidla T (1997) Keila Stage Oandu Stage Rakvere Stage Nabala Stage. In: Teedumäe A, Raukas A (eds) Geology and mineral resources of Estonia. Estonian Academy Publishers, Tallinn, pp 74–81 5. Huang S, Li X, Wang Y (2012) A new model of geo­environmental impact assessment of mining: a multiple­criteria assessment method integrating Fuzzy­AHP with fuzzy synthetic ranking. Environ Earth Sci 66(1):275–284. doi:10.1007/s12665­011­1237­z CrossRef 6. Ivanov KE (1975) Water exchange in peatlands. Gidrometeoizdat, Leningrad, pp 86–91 [in Russian] 7. Joosten H, Clark D (2002) Wise use of mires and peatlands. International Mire Conservation Group, International Peat Society, Saarijärvi, p 303 8. Jõgar P (1983) Ground­water flow models of Pandivere Upland (northeast Estonia). In: Proceedings of academy of sciences of ESSR. Geology 32, 2, 69–78 [In Russian, summary in English] 9. Karu V, Västrik A, Anepaio A, Väizene V, Adamson A, Valgma I (2008) Future of oil shale mining technology in Estonia. Oil Shale 25(2S):125–134 CrossRef 10. Kattai V, Vingisaar P (1980) Structure of the Ahtme tectonic disturbance. In: Proceeding of the academy of sciences ESSR. Geology 29, 2, 55–62 [In Russian, summary in English abstract] 11. Ketcheson SJ, Price JS (2011) The impact of peatland restoration on the site hydrology of an abandoned block­cut bog. Wetlands 31(6):1263–1274. doi:10.1007/s13157­011­ 0241­0 CrossRef 12. Kink H (1997) Karst and springs. In: Teedumäe A, Raukas A (eds) Geology and mineral resources of Estonia. Estonian Academy Publishers, Tallinn, pp 389–390 13. 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Boreas 40:367–378 19. Orru H, Orru M (2006) Sources and distribution of trace elements in Estonian peat. Symposium on peatlands—basin evolution and depository of records on global environmental and climatic changes location: Florence, Italy. Glob Planet Change 53(4):249–258. doi:10.1016/j.gloplacha.2006.03.007 CrossRef 20. Orru M (1975) Report of exploration­investigation works of peat deposits in KohtlaJärve County. Manuscript at depository of manuscript reports of geological survey of Estonia. Geological survey of Estonia, Tallinn (in Estonian, with Russian summary) 21. Orru M (1995) Estonian mires. Geological Survey of Estonia, Tallinn (in Estonian, with English summary) 22. Orru M (2010) Dependence of Estonian Peat deposit properties on landscape types and feeding conditions. PhD thesis, Publication of Tallinn University of Technology, Tallinn, pp 121 23. Orru M, Lelgus M (2003) Peat resources investigation of Soosaare peatland in Viljandi County, the Geological Survey of Estonia, Tallinn, pp 33 24. Orru M, Orru H (2008) Sustainable use of Estonian peat reserves and environmental challenges 15th Meeting of the Association­of­European­Geological­Societies location: Tallinn, Estonia Date: Sep 16–20. Estonian J Earth Sci 57(2):87–93. doi:10.3176/earth.2008.2.04 CrossRef 25. Orru M, Uebner M, Orru H (2011) Chemical properties of peat in three peatlands with balneological potential in Estonia. Estonian J Earth Sci 60(1):43–49. doi:10.3176/earth.2011.1.04 CrossRef 26. Parker I (1993) Mine pillar design in 1993: computers have become the opiate of the mining engineers. Mining engineering, 1993, July and August, 714–717 and 1047–1050 27. Pastarus J­R (2005) Improved underground mining design method for Estonian oil shale deposit. 5th international scientific and practical conference on environment, technology and resources. 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In: Teedumäe A, Raukas A (eds) Geology and mineral resources of Estonia. Estonian Academy Publishers, Tallinn, pp 163–177 34. Puura V, Vaher R (1997) Tectonics. In: Raukas A, Teedumäe A (eds) Geology and mineral resources of Estonia. Estonian Academy Publishers, Tallinn, pp 163–177 35. Reinsalu E (2001) Post technological processes in mined out areas. Estonian Science Foundation, Grant No. 3403, Tallinn (in Estonian) 36. Reinsalu E, Valgma I (2007) Oil shale resources for oil production. Oil Shale 24:9–14 37. Riet K (1974) About transmission capacity of Ordovician carbonate rock in the Estonia oil shale deposit. In: Proceeding of the academy of sciences ESSR. Chemistry. Geology 23, 3, 274–277 38. Regulation to room, pillars and safety zones calculation methods for underground oil shale mining (1997). Tallinn, pp 28 (in Estonian) 39. Sabanov S, Tohver T, Väli E, Nikitin O, Pastarus J­R (2008) Geological aspects of risk management in oil shale mining. Oil Shale 25(2):145–152 CrossRef 40. Scott B, Ranjtih PG, Choi SK et al (2010) Geological and geotechnical aspects of underground coal mining methods within Australia. Environmental Earth Sciences 60(5):1007–1019. doi:10.1007/s12665­009­0239­6 CrossRef 41. Sokman K, Kattai V, Vaher R, Systra YJ (2008) Influence of tectonic dislocations on oil shale mining in the Estonia deposit. Oil Shale 25(2):175–187 CrossRef 42. Systra YJ, Sokman K, Kattai V, Vaher R (2007) Tectonic dislocations of the Estonian kukersite deposit and their influence on oil shale quality and quantity. In: 15th MAEGS meeting 16–20 Sep 2007, Tallinn, Estonia. Abstracts. pp 74–76 43. Taylor JR (1982) An introduction to error analysis. In: Commins ED (ed) The study of uncertainties in physical measurements. University Science Books, California, p 272 44. Tousignant M­E, Pellerin S, Brisson J (2010) The relative impact of human disturbances on the vegetation of a large wetland complex. Wetlands 30(2):333–344. doi:10.1007/s13157­010­0019­9 CrossRef 45. Tutorial for digital mapping for Estonia geology (2008) Land Board (in Estonian) 46. Undusk V (1998) Safety factor of pillars. Oil Shale 15(2):157–164 47. Valgma I (2003) Estonian oil shale resources calculated by GIS method. Oil Shale 20(3):404–411 48. Valgma I (2009) Oil Shale mining­related research in Estonia. Oil Shale 26(4):150–445 CrossRef 49. Valgma I, Kattel T (2005) Low depth mining in Estonian oil shale deposit­Abbau von Ölschiefer in Estland. In: Kolloquium Schacht, Strecke und Tunnel 2005: 14. und 15. April 2005, Freiberg/Sachsen: Kolloquium Schacht, Strecke und Tunnel 2005: 14 und 15. April 2005, Freiberg/Sachsen. Freiberg: TU Bergakademie, 213–223 50. Valgma I, Reinsalu E, Sabanov S, Karu V (2010) Quality control of oil shale production in Estonian mines. Oil Shale 27(3):239–249 CrossRef 51. Väli E, Valgma I, Reinsalu E (2008) Usage of Estonian oil shale. Oil Shale 25(2S):101– 114 CrossRef 52. Wu Q, Liu S (2011) The classification of mine environmental geology problems in China. Environ Earth Sci 64(6):1505–1511. doi:10.1007/s12665­010­0503­9 CrossRef About this Article Continue reading... To view the rest of this content please follow the download PDF link above. Over 8.5 million scientific documents at your fingertips © Springer International Publishing AG, Part of Springer Science+Business Media View publication stats

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Oil Shale mining-related research in Estonia

txt: Oil Shale, 2009, Vol. 26, No. 4, pp. 445–450 ISSN 0208-189X doi: 10.3176/oil.2009.4.01 © 2009 Estonian Academy Publishers EDITOR’S PAGE OIL SHALE MINING-RELATED RESEARCH IN ESTONIA Finally the long-announced changes arrived, caused by environmental, geological and technological changes in oil shale mining sector. In addition, the biggest change has occurred with alteration of professionals’ generation. In most of the countries, the institutions dealing with mining are facing difficult questions – to continue or not to continue, and if, then how. Research, development and teaching work are facing a low at the moment. The biggest section in oil shale business in which saving and effectiveness could be achieved is the mining sector. It includes social and environmental restrictions in deposits, losses in pillars and separation of products and waste rock. Losses are closely related to backfilling and waste rock usage. Much smaller sections include production of oil, electricity and chemicals in which most of the research and development is performed today. Efficiency of oil shale usage depends manly on mining technology. 446 Editor’s Page Current urgent topics for investigating, testing and developing of oil shale mining related questions are backfilling, mechanical extracting of shale and digital modelling of mining processes. Estonian oil shale mining industry with its 90 years of history has been a test polygon for equipment manufacturers, geologists and mining engineers from Germany, Soviet Union, Finland and Sweden. These are the reasons why Estonia has recently hosted in average one international mining-related conference per year and is going to host the most important and highest level of the conferences – Annual General Meeting of the Society of Mining Professors “Innovation in Mining” (SOMP AGM 2010, http://mi.ttu.ee/somp2010). Mining research concerning Estonian oil shale deposits Several mining-related factors, such as changes in environment, underground conditions, landscape and property, tend to awoke public resistance. In order to create sustainable mining conditions, research on the natural environment and experiments conducted in mines and mined areas are required. Together with physical experiments, computer modelling is a widespread method in mining engineering. The principal task of modelling is to choose criteria and constraints satisfying all involved parties, as well as ways of presenting. In reaction to this, various restrictions for mining (mainly environmental ones) are created. In most cases, their argumentation is onesided, often subjective. As a result, it is not possible to exploit a large part of deposits due to environmental restrictions, but also due to expiration of evaluation criteria of the supplies of resources. Part of the problems is caused by miners that do not apply environmentally friendly mining technologies. Mining environment is understood as the entity including resources (deposits and groundwater), land (agricultural and housing land), engineering and technology. Research has shown that ground and landscapes changed by mining can afterwards be of better quality than before. If reclaiming is planned skilfully, the soil, landforms, forest, water bodies and agricultural land can be more valuable than before mining. All this is the basis for developing acceptable, environmentally friendly mining. Acceptable mining requires engineering research concerning both natural and technogenic environment, e.g. modelling and pilot projects. As such research is voluminous, computer modelling has become the principal tool in solving problems related to all sorts of developments, technologies and effects. The key issue is defining criteria and restrictions that satisfy all the involved parties. Creating models and estimation criteria requires miningrelated expertise and a database acquired from measurements, experimenting and laboratory testing. Modelling is followed by laboratory and industrial experiments, which require profound know-how. The experiments include e.g. chronometry of technological productivity, geometric and geological measurements, and measurements of rock quality. The parties that compose mining plans, development plans and estimations of environmental effects Editor’s Page 447 have acquired planning and modelling software for various purposes, which causes some problems: the geological database requires skilful treatment; data exist in several geodetic coordinate systems and include partly obsolete stratigraphic terminology. Unfitting coordinate systems disturb the usage of cross-use of spatial data in various geoinformation databases (digital maps, border files, land registers, building registers, databases of technological networks of enterprises, etc.). This creates further problems related to mined areas. Most environmental restrictions, which have to be taken into account in mining and building, are not based on real measurements. Usually the restrictions are two-dimensional and do not take into account the structures of the geological environment. Such vagueness does not support precise engineering calculations or modelling. Basic modelling systems that are designed in developed mining countries are principally meant for deep deposits. However, in Estonia there are blanket deposits, which cause wider environmental effect of mining. Because of that, imported systems have to be adapted. Mining is possible in any circumstances, provided that sustainable mining environment has been created. In other words, with the proper choice of mining technology, the effect of mining has been damped below the level that the nature and man can tolerate. The methodology and criteria for planning, designing, modelling and accepting of sustainable mining environment will provide the basis for mineral raw material that the economy requires, both in the near and far future. The principal direction of developing mining technology is filling the mined area. This provides control over majority of environmental effects. For instance, filling the workings decreases the loss of resources and land subsidence, and at the same time provides usage for stockpiling. Filling the berms of surface mine decreases dewatering; harmless waste can be used for filling open mines and in this manner offer new building land. Local land subsidence related to mining may extend also to technological networks. It is possible to find out deformation parameters by geodetic monitoring. Taking these parameters into account enables to model further the extent and effect of the deformation. Modelling, including digital planning, is aimed at gaining and creating the following: mining indicators needed for making decisions, future scenarios of mining oil shale and building material, support for development planning at state and regional level, technological solutions that take into account all possible environmental effects and social reactions, new output: project solutions, theme maps, inquiries, zoning, evaluations of crises or risks, optimal methodology for gaining, storing and using information, having in mine requirements for various purposes and levels, more effective usage of geological, technological and spatial information, additional functionality of the database. The optimal solution is obtained by modelling. The most general but also dominant criteria are: minimal effect on man and nature, minimal amount of 448 Editor’s Page residual and waste, maximal economic profit, also in other fields not only in the mining industry. The problem includes several criteria, and its solving requires both theoretical and computational solutions. Principal methods are related to introducing sensors, measuring equipment and mining condition experiment, matching structures of various data and modelling based on them. The methods are: mapping the modelling criteria, indicators and processes of the mined areas; experimenting the possibilities of application, compatibility and results of mining software; applying laboratory experiments and fieldwork in modelling; creating models for blanket deposits (methodology in modelling MGIS, i.e. mining geoinformation system, models of new mines, changes in ground conditions, environment (modelling and analysis of groundwater dynamics, effects of dust, noise, etc.), geotechnological models in mined areas); applying seismological methods for developing theory for collapse risk, analysis methods for creating spatial models from geodetic spatial information, studies on material properties for developing theory for criteria for rock breakage, dendrochronologic studies for monitoring changes caused by collapses and changes in the water regime. As a result, conditions for creating mining environment satisfying all involved parties (industry, state, public, decision makers) will be developed, applicable for any deposit of any resource. A system of criteria of evaluating the mining environment will be designed. This research provides for mining science a new level of digital modelling of blanket deposits, basing on long-term experiments and modern digital planning. The research results will be applied in compilation of the state development plan, planning mined areas, as well as in teaching and science. The results are relevant principally for users of land and ground (builders, geologists, hydrogeologists, hydrologists, mining engineers and reclaimers). The results provide better understanding between the public and the miners, and further a basis for well-argumented communication and promotion for economy in the manner that satisfies both parties. In recent years, there has been a world-wide initiative for research, creating the concept of sustainable mining, using relevant indicators and making decisions based on them. MMSD (Mining, Minerals, and Sustainable Development), SDIMI (Sustainable Development Indicators for the Minerals Industry) and other international networks emphasize the need for creation of a concept for regional sustainable mining, relevant for local conditions. At the same time, modelling systems are being built and usage of non-traditional fuels is being started. About three decades ago oil-shale mines of the former USSR including Estonia did not use the progressive mining methods with continuous miner, which are most suitable for the case of high-strength limestone layers in oilshale bed. Therefore, oil shale mining with blasting has been used as a basic mining method in Estonian minefields up to now while continuous miner was tested for roadway driving only. As for cutting, the installed power of Editor’s Page 449 coal shearers and continuous miners has increased enormously since the original work. The actual state of the market has changed, and a wide range of powerful mining equipment from well-known manufacturers like DOSCO, EIMCO, EICKHOFF, etc. is available now. Estonia has 30 years of experience in cutting with longwall shearers which were not capable of cutting hardest limestone layer inside of the seam. Tests with road headers have been carried out in the 1970s. Additionally Wirtgen surface miners have been tested (SM2100 and SM2600) for two years as well as SM2200 and Man Tackraf surface miner, and currently the testing of Wirtgen surface miner SM2500 for high selective mining in an open cast mine is being performed. The main field to be developed in addition to mine backfilling is mechanical extraction of oil shale. Potentially this allows increasing oil yield, decreasing CO2 pollution, decreasing ash amount, decreasing oil shale losses, avoiding vibration caused by blasting, avoiding ground surface subsidence (in the case of longwall mining), increasing drifting and extracting productivity compared with current room and pillar mining, increasing safety of mining operations. The final aim of the research is to use BAT (best available technology) for underground mining in areas with arduous conditions of coal and oil-shale deposits. The main problems to be solved are: selective cutting of oil shale (15 MPa) and hard limestone (up to 100 MPa), roof support at the face, stability of the main roof, roof bolting, pillar parameters, backfilling with rock or residues (ash) from oil production, water stopping and pumping in problematic environment (30 m3 /t expected). Currently room and pillar mining with drill and blast technology is used underground. Supporting is done with bolts. Mining production is in total around 14 Mt/y, including 7 Mt/y underground. Total raw material amount underground is 12 Mt/y. Tests are made for opening new mines, with total production 15 Mt/y. Continuous miners keep playing a major role in the underground industry in over fourteen countries worldwide. Estonia’s oil-shale industry is at the beginning of introducing modern fully mechanized continuous miner systems, which could increase productivity and safety in the underground mines. A longitudinal cutting head-type miner was first introduced in the former Soviet Union by modifying the Hungarian F2 roadheaders and in the 1970s in Estonia by modifying the Russian coal roadheader 4PP-3. Evaluation of breakability was performed by a method developed by A. A. Skotchinsky Institute of Mining Engineering (St Petersburg, Russia). For this purpose over a hundred samples produced by cutting of oil shale and limestone, as well as taken in mines by mechanical cutting of oil shale were analysed. Evaluations were made for using coal-mining equipment for mining oil shale. Comparative evaluations were made by the experimental cutting of oil shale in both directions – along and across the bedding, including also mining-scale experiments with cutting heads rotating round horizontal 450 Editor’s Page (transverse heads) and vertical axes (longitudinal heads). In both cases the efficiency was estimated by power requirement for cutting. The feasibility was shown by breaking oil shale in direction of cutting across the bedding by using cutting drums on horizontal axis of rotation. The research also evidenced that the existing coal shearers proved low endurance for mining oil shale. Therefore, there arose the problem of developing special types of shearers for mining oil shale or modifying the existing coal shearers. It was further stated that the better pick penetration of the longitudinal machines allows excavation of harder strata at higher rates with lower pick consumption for an equivalent-sized transverse machine. It was reported that with the longitudinal cutting heads the dust forming per unit of time decreases due to smaller peripheral speed. The change in the magnitude of the resultant boom force reaction during a transition from arcing to lifting is relatively high for the transverse heads, depending on cutting head design. Specific energy for cutting across the bedding with longitudinal heads is 1.3–1.35 times lower which practically corresponds to the change of the factor of stratification. These are the questions waiting for answers in the near future for effective oil shale extraction in Estonia and in similar mining conditions. In spite of current economic problems, still everything begins with mining. Ingo VALGMA Head of Department of Mining of Tallinn University of Technology, Head of Estonian Mining Society, President of the Society of Mining Professors / Societät der Bergbaukunde

Developing computational groundwater monitoring and management system

Paper: Developing computational groundwater monitoring and management system for Estonian oil shale deposit

Paper: Technogenic water in closed mines

Paper: Technogenic water in closed mines Oil Shale, 2006, Vol. 23, No. 1 ISSN 0208-189X pp. 15–28 © 2006 Estonian Academy Publishers The present paper is based on the results of the research conducted in 2004 by the Department of Mining of the Tallinn University of Technology and Estonian Oil Shale Company. The state of the technogenic water body that has formed in the central part of the oil shale deposit is analysed: the water level in the area of the stopped and closed mines, water amount and move- ment direction, water quality and its changes. The state of the water is assessed and predicted using modelling of the water tables, statistical analysis of the water quality parameters and the pilot model for describing the migration of water. The results show that the technogenic water body studied is in a relatively stable state, and the quality of the groundwater in that area is fast improving approaching the drinking water standards. Introduction The Estonia oil shale deposit comprises about ten closed and stopped deep mines that are fully or partly filled with water (Table 1). Eight mines in the central part of the deposit: Ahtme, Kohtla, Kukruse, Käva, Sompa, Tammiku and mines Nos. 2 and 4 form one water body. After Ahtme mine was filled with water in December 2004 (Fig. 1), the water body turned relatively stable. Ubja mine and joint Kiviõli and Küttejõu mine are located in the western part of the deposit, farther away from the other mines. In addi- tion to oil shale mines, Sillamäe uranium mine (1949–1952) [1], and Ülgase (1922–1938) and Maardu phosphorite mines (1942–1965) have been closed in Estonia. The water regime in these mines has not been studied yet and is not discussed in the present paper. * Table 1. Closed and flooded underground oil shale mines Mine Closed – (pumps were stopped) Mined area, km2 * Water table a.s.l., m Outflow regulating the water table Approximate water volume, 106 m3 Central part of the deposit: Kukruse 1967 13 51–54 Mostly into Käva and Jõhvi mines 3.5–6** Käva and Käva-2 1973 18 51–52 From an old adit into Vahtsepa ditch 9–11** Mine No. 2 (Jõhvi mine) 1974 13 51–56 Mostly into Tammiku mine, during flood to Jõhvi city 10–11** Mine No. 4 1975 13 41–42 Mostly into neigh bouring mines 3–8** Tammiku December 1999 40 44–48 Into the Kose River and Viru mine 34 Sompa February 2000 27 40–45 Into neighbouring mines 23 Kohtla June 2001 17 39–42 Into Aidu opencast 13 Ahtme December 2001 – December 2002 35 ≈ 47 From drill holes and springs into Sanniku brook 36 Separate mines in the western part of the deposit Kiviõli & Küttejõu 1989 29 41 ± 0.5 From a ditch into the Purtse River Up to 29 Ubja 1960 2 ≈ 55 From an adit into the Toolse River Not determined Total ≈ 170 * [5] ** Depending on the water level [6] As a rule, the mine workings and groundwater cone of depression formed during mining fill with water after the cease of mine pumping. The degree of filling depends on the mining depth and the height of outflow. The tunnels of Ahtme, Sompa and Tammiku mines are completely, those of mines Nos. 2 and 4 almost completely water-filled. The rest of the mines (Kiviõli, Kukruse and Käva) contain areas with dry floor. The museum founded in Kohtla mine is dry because of to the draining effect of Aidu opencast and the water barriers surrounding the exposition area. The water level changes depending Technogenic Water in Closed Oil Shale Mines 17 10 15 20 25 30 35 40 45 50 2002 2003 2004 2005 Water level, m Tarakuse well Pagari well Fig. 1. Increase in the water table in closed Ahtme mine on the amount of precipitation and water exchange with neighbouring mines. The rate and amplitude of the changes differ from mine to mine. Several problems have arisen from the flooding of the closed mines. First, the technogenic water body started to affect the amount of the water pumped out of the working mines and its seasonal variation [2]. Clearly, the water of the closed mines will influence also the new mines, planned to be constructed in the Ojamaa and Uus-Kiviõli mine fields. Second, the environ- ment is affected by the water that in several places has risen to the pre- mining level (of the year 1945) and by the new springs formed. Several projects have been undertaken to fight the flooding, and it has turned out that no sufficient source data for mine planning are available. Third, the water of the closed mines is an easily accessible water resource, thus it is important to know and predict its quality [3]. Prediction of the mine water quality is essential also because of the fact that groundwater elevation in the mine field has started to affect the water supply of the region – the water richer in sulphates runs into the outdated and leaky common wells. It has also been prognosticated that if the groundwater table rises higher than 45–47 m, the water in the Ahtme mine field will affect the water level and quality of the Vasavere intake [4]. Fourth, the land above old mines has subsided and the rocks are fractured, therefore the technogenic groundwater is weakly protected and the contribution of precipitation to groundwater formation is very high. Water level The present study is based on the water level measurement data (incl. archive data) provided by the Estonian Oil Shale Company, Geological Fig. 2. Map of the technogenic water body Technogenic Water in Closed Oil Shale Mines 19 Survey of Estonia and Municipality of the town of Jõhvi. The water levels of the Keila–Kukruse, Lasnamäe–Kunda and Nabala–Rakvere aquifers, closed mines and main outlets were measured on an average period of 20 years. New data were obtained in the years 2003 and 2004. Field works and monitoring started in the spring of 2004 and are still going on. An essential part of the research was the modelling of the level of the Keila–Kukruse aquifer in the stationary regime. The modelling area included the central part of the deposit – underground mines and Aidu opencast. Data from about 50 observation wells were used. The water level of working mines was described at the level of the oil shale bed floor. Closed mines were treated as independent water sub-bodies, where the water level is constant at a certain moment of time (Table 1). The MapInfo Professional software was used, combined with the modelling package Vertical Mapper. The comparison and calibration of the intermediate results obtained and discussions held showed that the best interpolation method was triangulation with smoothing, because in that case interpolation takes place only between data points or observation wells, without modelling the situation outside the study area. During the first stage of the research the state of the water body in August 2004 was assessed. According to the measurements and calculations performed, precipitation accounts for up to 70% of the water pumped out of mines [2]. The autumn–winter season of 2004 was rich in precipitation, with little snow and relatively warm. Therefore it could be expected that Ahtme mine would fill with water sooner than predicted [4]. To check that hypothesis, the model was calibrated at the second stage of the research in December 2004. The contour map of the modelled water table is shown in Fig. 2. By continuous improvement of the existing and addition of new data more than ten two- and three-dimensional map versions were completed. The model enabled us to assess the water levels in different mines and their border areas and to make assumptions and predictions about the water move- ment directions. Water quality In the years 2000–2004 the department of environmental services of the Estonian Oil Shale Company had the waters of all closed mines analysed. The samples were taken at six sites in four mines in different seasons. Analyses were made at the central laboratory of the Estonian Oil Shale Company (3 analyses), in Tartu Environmental Research Ltd. (2 analyses) and in the Geological Survey of Estonia (12 analyses). Up to 16 quality parameters were determined. The results of the analyses are presented in Table 2. The quality parameters are arranged in Table 2 in the decreasing order of the variation in measurement results. At first glance only the average contents of iron, sulphates and phenols obtained for the observation period do not meet the drinking water standards. This cannot be a final conclusion. The average Table 2. Water quality parameters in closed Ahtme, Kohtla, Sompa and Tammiku mines Quality parameter Unit Number of measurement results Numerical data for the entire period (2000–2004) Leachates Total Certain numerical values Arithmetical mean Standard deviation Variation coefficient Max. levels permitted in drinking water Total Fe mg/l 14 10* 0.69 1.16 1.67 <0.2 NO3 - mg/l 15 11* 11.7 18.55 1.58 <50 NO2 - mg/l 12 7* 0.015 0.0166 1.10 <0.5 SO4 2- mg/l 15 15 342.4 240.2 0.70 <250 Dry residue mg/l 14 14 845.5 569.6 0.67 – Mg2+ mg/l 15 15 51.6 32.58 0.63 – K+ mg/l 13 13 12.9 8.11 0.63 – Ca2+ mg/l 15 15 174.5 107.6 0.62 – Na+ mg/l 14 14 10.4 6.33 0.61 <200 Cl mg/l 15 15 16.4 9.74 0.59 <250 Total hardness mge/l 13 13 13.72 7.04 0.51 – Oil products mg/l 15 4* 0.15 0.073 0.49 <0.05 Conductivity μS/cm 14 14 1095 477.6 0.44 <2500 NH4 + mg/l 12 2* 0.017 0.0064 0.39 <0.5 Total phenols mg/l 15 4** 0.0017 0.00049 0.28 <0.0005 pH 15 15 7.1 0.33 0.05 6.5–9.5 * due to the lack of a certain numerical value the result was smaller than the preciseness of the laboratory tests, but not exceeding the limits permitted in drinking water ** due to the lack of a certain numerical value the result was smaller than the preciseness of the laboratory tests, in two cases not exceeding the limits permitted in drinking water; rest of the samples gave no unique result Notes: Quality parameters are ordered according to the variation coefficient. The shaded lines contain the measurement results the average of which does not meet the Estonian drinking water standard. The content of benzo(a)pyrene was measured in 11 samples. The results are not included in the table because no certain numerical values were obtained. In all samples the benzo(a) pyrene content was lower than the permitted maximum value. and standard deviations given in the table have been calculated for all closed mines and for the entire observation period, thus they characterize only the data set and not the quality of water or a particular mine. Variation in the measurement results is caused by influential as well as random factors. Influential factors are the sampling site (mine) and the time span that has passed since the closure of the mine. Let us treat this assumption as a working hypothesis. A random factor is the season when sampling was performed. For example, in the years 2000 and 2001 samples were taken in summer, in 2002– 2004 in autumn. Surely the water quality parameters depend also on the Technogenic Water in Closed Oil Shale Mines 21 location of the sampling site in the mine field. Some part of variations result from the methodology of sampling and laboratory tests. The reliability of iron content analyses carried out in different laboratories could be questioned. The phenol content of mine water, measured repeatedly during mining, has been 0.003 ± 0.001 mg/l, except for Kiviõli mine, which has been strongly affected by chemical industry. Here the phenol content of mine water was 0.38 mg/l [7]. For preliminary checking of the working hypothesis we conducted a two- factor (place and time) variation analysis of the sulphate and iron contents of Tammiku and Sompa mine waters. The results of sulphate analysis are given in Table 3. We can see that the hypothesis of the influence of place and time on the sulphate content of water is relatively strong (probability of a counter- hypothesis 18.0 and 18.8% respectively). The residual standard deviation (187 mg/l), however, is too large for making definite conclusions. Obviously the result is influenced by taking samples in different seasons. An analogous result was obtained by the variation analysis of the iron content, whereas the impact of time turned out to be small. Possibly this could result from the treatment of samples in different laboratories. In spite of great uncertainty of measurement, the sulphate and iron contents decrease with time. This trend is depicted by graphs in Fig. 3. As could be expected, the purification of water is best described by the exponential function. The constants in the formulae (801 and 0.77 mg/l, respectively) characterize the average concentrations at the initial moment of the dilution process (at the closure of mines) and the time factors (–0.386 and –0.507, respectively) show the rate of water purification. The half-life of the concentration calculated on the basis of time factors, i.e. the time period during which the content of a component decrease twice, is about 1.8 years for sulphates and 1.4 years for iron. From the half-life and graphs we may presume that in about five years after the closure of a mine the content of sulphates and iron decreases below the maximum permitted level in drinking water. The highest permitted content of iron in first-class drinking water is 0.2 m/l and that of sulphates 250 m/l. The data on all mines are included in the graphs of Fig. 3. The measure- ments revealed varying initial concentrations of sulphates for different mines. The highest concentration was recorded in the first sample from Ahtme mine, the lowest in Kohtla mine. Actually, this is not the initial level, since the first samples were taken 4–11 months after the pumps had been stopped. Approximating the results obtained from the samples of each mine separately, we get theoretical dilution of the initial concentration level at the zero moment, about 2200 mg/l for Ahtme and 300 mg/l for Sompa. These values refer to a relation between the depth of the mine and the initial concentration of sulphates. The hydrogeological background of this pheno- menon is discussed by Erg [3]. Table 3. Results of the variation analysis of the content of sulphates Source of Variation df MS F P-value Mines (Tammiku, Sompa) 1 91681 2.63 0.180 Years (2002–2004) 4 92788 2.66 0.183 Error 4 34924 Residual Standard Deviation 187 mg/l Total 9 SO4 2- = 801 e-0.386 t, mg/l R2 = 0.46 10 100 1000 10000 01234567 t - closed, years SO42- - sulphate content, mg/l 250 mg/l Fe = 0.77 e -0.509 t , mg/l R2 = 0.39 0.01 0.1 1 10 01234567 t - closed, years Fe content, mg/l 0.2 mg/l Fig. 3. Decrease in the content of SO4 2- and Fe in closed mines. 250 mg/l and 0.2 mg/l – maximum permitted levels in drinking water. The water quality parameters for which we had at least 14 reliable measurement results (pH, electric conductivity, total hardness, Cl- , dry Technogenic Water in Closed Oil Shale Mines 23 residue, Na+ , Ca2+, Mg2+, K+ and SO4 2- ) were subjected to correlation analysis. From the analysis we could conclude the following: • The content of sulphates can be considered a good indicator of mine water quality, because it correlates well with most of the other water quality parameters, except for K+ . • Electric conductivity can be successfully used for rapid assessment of water quality, because it correlates well with sulphates as well as with other main parameters (except for K+ ). • pH is not informative enough, because it does not correlate with any other water quality parameter. Pilot model of water exchange Continuous water exchange is going on between the closed mines. The water penetrating into mines is derived mostly from precipitation, less from groundwater. The part of the water not flowing out of the mine (Table 1) infiltrates into the neighbouring mines or feeds aquifers. The water pumped out of the working mines is formed of precipitation, groundwater and the water coming from closed mines. Intensity of water exchange depends on the length (L, km) and thickness (l, m) of the barrier left between the mines, difference between the water levels of neighbouring mines (dh, m) and permeability of the barrier and overburden (km, m2 /d). The longer and thinner is the barrier, the greater is the water level difference in neighbouring water bodies, and the higher is the permeability of rocks in the areas separating the mines, the more intensive is the exchange of water. The water levels of the closed mines are precisely known. The measure- ments of barriers can be obtained from the plan of mining works, but the length and thickness of the barriers are highly variable. Little data are available on the permeability of pillars and bedrock. As seen in Table 4, the permeability of the Keila–Kukruse aquifer differs up to 10 times within the limits of the deposit. Water permeability is largely affected by the geological disturbance of the Earth crust (mostly karst zones), which makes the aquifer highly aniso- tropic [8, 9]. In the Estonia mine field twofold difference in the permeability in the northeastern and southeastern directions has been recorded. According to the data by Domanova, anisotropy is especially great in the area of tectonic dislocations, where permeability in various directions may differ several times. Water exchange between the mines is inhibited by extensive karst zones running along the mine field boundaries between Sompa and Viru, and Ahtme and Tammiku mines. At the same time, karst zones running transversely to the mine boundary increase the water exchange between Sompa and Kohtla mines. Additionally, the water exchange is affected by the properties of the mined area, which depend on the roof handling methods used. In the area Table 4. Permeability of the Keila–Kukruse groundwater aquifer in the mining district Filtration module Publication District Permeability, m2 /d Estimated difference in water tables, m m/h m/d Kohtla – Aidu, northern part 1200 5 10 240 Kohtla – Aidu, central part 780 10 3.25 78 [8] Kohtla 6–60 Viru 10–40 [7] Aidu, generalized 393 10 1.6 39 Ahtme, generalized 335 10 1.4 34 [4] Tammiku 4–20 Ahtme 1–15 [7] Ahtme – Estonia 90 10 0.38 9 [4] No. 2 – Tammiku 0.24 6 [10] mined using roof caving the water-bearing horizon is thicker and of higher permeability than in the area of room-and-pillar mining. Because of high uncertainty the calculation of the water amounts moving between the closed mines is complicated, not only due to the variability in L, l, k, but also due to the lack of the relation uniquely describing all the situations. Therefore the present study makes use of the balance method, which unites the amounts of the water pumped out of the working mines, and of precipitation and groundwater infiltrating into the mine. The relation between these amounts is expressed by the approximate formula qij = 365.25 × Lij × kij × (dhij/2) / (1000 × lij), where qij – the amount of the water migrating from one mine (i) to the other (j), million m3 /y, Lij – length of the barrier between these mines, km, lij – average thickness of the barrier, m, dhji – difference between the water levels of two closed mines at the moment of modelling, m, kij – factor characterizing the permeability of the area between the mines (barriers and overlying rock), which, with some reservation, can be considered as generalized permeability, m2 /d. As model input we use the measurements of the barriers between the mines, volume of the water pumped out of the working mines (especially changes in it due to the closure of neighbouring mines), amount of precipita- tion and its relation to mine pumping [2]. The variable parameter of the Technogenic Water in Closed Oil Shale Mines 25 model is generalized permeability, which is used to balance the model. Permeability was fitted into the model taking into consideration the informa- tion available (Table 4), location of mines with respect to tectonic fault zones and the orientation of the karst zones lying between the mines. The balanced model can be used for calculating the migrating water amounts by fluctuations in water level, for example during floods and heavy rains, but also for planning water level regulations. The model output is the matrix of water exchange (Table 5), where • “North” denotes the northern closed mines No. 2, Kukruse, and Käva and its satellite mines • “West” denotes the western closed mines Kohtla, Sompa and No. 4 • “Vasavere” is the area east of Ahtme and Estonia mines • The water amounts in the matrix of water exchange are given in million m3 /y, whereas (+) shows the amounts infiltrating into the mine (i) from the mine (j) and (–) shows the amounts migrating from the mine (i) to the other mine. Explanations to the matrix of water exchange are given in Table 6. Water movement inside the water body and the amounts of mine pumping are shown in Fig. 1. The values presented characterize the state of the water body in the year 2004, but as we have to do with a pilot model, these are all approximate. Table 5. Matrix of water exchange, year 2004, 106 m3 /y ↓Elements of the water body → Aidu Estonia Viru Ahtme Tammiku North West Vasavere Jõhvi city Sum Working mines: Aidu 0.00 0.00 0.00 0.00 0.00 0.00 14.46 0.00 0.00 14.46 Estonia 0.00 0.00 1.64 6.48 0.00 0.00 0.00 0.48 0.00 8.60 0.00 0.00 –1.64 0.00 0.18 7.23 0.00 3.07 0.00 0.00 8.83 Technogenic water body; closed mines (sub-bodies): Ahtme 0.00 –6.48 –0.18 0.00 0.07 0.00 0.00 –1.07 0.00 –7.65 Tammiku 0.00 0.00 –7.23 –0.07 0.00 2.28 –1.69 –0.50 0.00 –7.22 North 0.00 0.00 0.00 0.00 –2.28 0.00 –4.60 0.00 –0.15 –7.03 West – 14.46 0.00 –3.07 0.00 1.69 4.60 0.00 0.00 0.00 –11.24 Geographical sites: Vasavere 0.00 –0.48 0.00 1.07 0.50 0.00 0.00 0.00 0.00 1.09 Town of Jõhvi 0.00 0.00 0.00 0.00 0.00 0.15 0.00 0.00 0.00 0.15 Table 6. Water exchange between mines Mines, techno- genic water sub-bodies and geographical sites Water exchange, 106 m3 /y Comments Working mines: Aidu 14.46 Inflow from closed Kohtla mine Estonia 8.60 Main inflow from closed Ahtme mine, less from the direction of working Viru mine, partly also from the east Viru 8.83 Inflow from closed Tammiku and Sompa mines, slight outflow into Estonia mine Technogenic water body; closed mines (sub-bodies): Ahtme –7.65 Outflow mainly into Estonia mine and into the catchment area of the Pühajõgi River through springs and outflow wells Tammiku –7.22 Intensive water exchange with other parts of the water body, out flow into the catchment area of the Pühajõgi River through a caving at Kose Northern closed mines Käva, Kukruse and No. 2 –7.03 Feeds other closed mines, outflow via Vahtsepa ditch into the Kohtla River Western closed mines Kohtla, Sompa and Mine No 4. –11.24 Intensive water exchange with other parts of the water body, feeds mostly Aidu opencast Geographical sites: Vasavere 1.09 Water inflow mostly from Ahtme mine, to some extent also from closed Tammiku mine Town of Jõhvi 0.15 Water infiltrates from closed mine No. 2 Conclusions and recommendations No great changes in the water level of closed mines and its seasonal variation are expected if no measures are taken. The situation should not change after the closure of presently working mines either. In future the water level of flooded Aidu opencast will be regulated by an outlet into the Ojamaa River at 40–42 m level, which will be also the common water level in Kohtla and Sompa mines. In the area of Viru and Estonia mines the groundwater will rise to the pre-mining level, which will result in an increase in groundwater flow into the Pühajõgi River at the eastern margin of Tammiku and Ahtme mines. It may turn necessary to regulate water level in the mining district. In order to reduce the flow of groundwater from mine No. 2 to the lower, area of the town of Jõhvi, the following options could be considered: • outlet of water at 51 m level at the northern boundary of the mine, near the adit of unbuilt mine No. 1 Technogenic Water in Closed Oil Shale Mines 27 • blasting of the barrier between mine No. 2 and Käva and Tammiku mines to enable water outflow towards the Kohtla River (at a level of 51 m) or into the Pühajõgi River (at 45–47 m level) • building of a pumping station regulating the water level and operating seasonally, but this is evidently not efficient due to great expenses. In order to reduce the water amounts penetrating into working mines and towards Vasavere intake, it would be purposeful to lower the water level in several closed mines: • to 45 m level in Tammiku mine, by dredging the present outlet • to 42–43 m level in Ahtme mine, by drilling artesian wells The quality of the water of closed mines is improving. The content of sulphates and iron in mine water decreases and in about five years after the closure of the mine is below the maximum level permitted in drinking water. Monitoring the water quality in closed mines should be aimed mostly at protecting the water body from surface-derived pollution. The sampling methods should be improved, with indicating justified times and places for taking water samples. In some cases the number of parameters measured could be reduced. As no reliable data are available about the formation and distribution of phenols in the water of closed mines, corresponding investigations are needed before the use of the water. Although phenols are generally believed to originate from the waste of shale oil plants or from burning spoil dumps, the possibility of their formation during decomposition of kerogen in water- filled mines cannot be excluded either. This hypothesis deserves further special study. Acknowledgements This paper was written within the framework of Grant 5913 of the Estonian Science Foundation “Usage of mined-out areas”, using the database of research No. 416L “Forecast of hydrogeological changes resulting from the activities of the Estonian Oil Shale Mining Company” carried out by Tallinn University of Technology. REFERENCES 1. Reinsalu, E. Sillamäe uranium mine // Environment Technics. 2001. No. 2. P. 40–45 [in Estonian]. 2. Reinsalu, E. Changes in mine dewatering after the closure of exhausted oil shale mines // Oil Shale. 2005. Vol. 22, No. 3. P. 261–273. 3. Erg, K. Changes in groundwater sulphate content in Estonian oil shale mining area // Oil Shale. 2005. Vol. 22, No. 3. P. 275–289. 28 E. Reinsalu, I. Valgma, H. Lind, K. Sokman 4. Savitski, L., Savva, V. Prognosis of hydrogeological changes in the mining district of the Estonian oil shale deposit, stages 1–3, 2001 [in Estonian] 5. Reinsalu, E., Toomik, A., Valgma, I. Mined out land, Tallinn, 2002 [in Estonian]. 6. Butakova, A., Jürgenfeldt, G., Reinsalu, E. Assessment of the mine water volume of water-filled oil shale mines // Gorjutšie slancy. 1980. No. 1. P. 6 [in Russian]. 7. Parahonski, E. Formation of mine water in oil shale mines and opencasts and mine drainage. Tallinn, Valgus, 1983 [in Russian]. 8. Domanova, N., Reinsalu, E. Analysis of hydrogeological conditions in Oktoobri opencast, Topic 0107, Stage HD No. 1, Estonian Branch of A. Skotchinski Institute of Mining Engineering, 1979 [in Russian]. 9. Domanova, N. Formation and forecast of water flowing into the mine workings driven into carbonate rocks with uneven infiltration properties. Candidate’s thesis, A. Skotchinski Institute of Mining Engineering, 1986 [in Russian]. 10. Domanova, N. Predicted increase in the water inflow into Viru mine due to the flooding of Tammiku mine. Estonian Oil Shale Company, Jõhvi, 1999. Manu- script [in Russian]. Recieved June 20, 2005

Paper: POST-STRIPPING PROCESSES AND THE LANDSCAPE OF MINED AREAS IN ESTONIAN OIL SHALE OPEN CASTS

1.1 POST-STRIPPING PROCESSES AND THE LANDSCAPE OF MINED AREAS IN ESTONIAN OIL SHALE OPEN CASTS [SLIDES] I. VALGMA The present study describes creating a digital map of oil shale surface mining technology and evaluating mining influences on the landscape. The data from the digital map of the Sirgala open cast show a constant increase in the overburden thickness. Overburden material thickness influences directly the future landscape but it also sets limits to stripping equipment parameters and productivity. The present open cast landscape was divided into four classes: afforested area, area with poor vegetation, graded area, and spoils. The second purpose of the study is saving information in an easily accessible form for the future. For this purpose geographic information system for mining is used. Introduction The minerals of Estonia are excavated in the amount of 10.5 million m3 per year. Yearly 7.4 million m3 of oil shale is mined, and half of this is mined in the open cast mines. The total surface mining amount in Estonia is 6.7 million m3 per year, and 54 % of it stands for oil shale mining. From this data a general rule follows: 1/3 of the volume of mined minerals comes from oil shale underground mining, 1/3 from oil shale surface mining, and 1/3 from surface mining of other minerals. Mining areas could be divided into five reclamation categories. First - mud excavation area - where mining takes place under water, is no subject for reclamation. Second - clay mining pits - are reclaimed to water storages, ponds or landfills. Third - sand and gravel quarries - are graded or formed as ponds. Fourth - limestone and dolostone quarries - form relatively deep ponds or are filled with waste. Among small-scale mining their reclamation is the most problematical one. Fifth - oil shale, phosphate rock and peat mining areas - are large due to thin horizontal bedding and require special reclamation. The largest Estonian surface mines are described as an example of large-scale mining operations and post-stripping processes. These open cast mines are largest by both area and production capacity and so cause also the largest influence to the environment and landscape. These three are the Aidu, Sirgala and Narva oil shale open casts, situating in the deposit wings where overburden thickness is smallest (Fig. 1). On the whole 120 km2 of overburden have been stripped in these mines. Fig. 1. Estonian oil shale deposit Calculations and charts in the present paper describe mostly the Sirgala open cast as the largest open cast mine in Estonia. Detailed description of the past processes in the mined-out areas let us understand, predict and save the information about several technological and environmental influences. Many of processes explain the reasons of forming the present landscape in these areas. The data about the equipment can help planning next trenches working in similar conditions. The data about steps of technological development of surface mining help us to retain historical data about large mineral extraction areas. A geographically referenced database represents a most suitable tool to study all these problems. Methods Geographic information system (GIS) for mining is used for describing and analysing spatial mining-related data. GIS is used for describing, in addition to technological problems, also post-technological processes. The main result is a digital map illustrating the oil shale mining technology. The present study presents the second stage of the map creation at the Mining Institute of Tallinn Technical University. During the first stage underground mining technology was mapped, the second stage includes the map of surface oil shale mining [1, 2]. Information on the map was taken from the technological maps of oil shale open casts, geological investigations, and aerial photographs and from the digital Estonian base map. Fig. 2. Mining sections in the Sirgala open cast The study included the following steps: collecting maps and references about the area, scanning, digitising and vectorising map data. The contours of the blocks mined in every mine section during a year were extracted and mapped. The database includes, in addition, the year of mining, height of the ground above the sea level and overburden thickness. As the result a digital surface mining map was created. The map (Fig. 2) includes stripping data and also aerial photographs and represents a basis for studying stripping dynamics, areas, volumes and landscape situation. Discussion Mapping calculations show that the total area of the mined sections in the Sirgala open cast is 6,532 ha. Aerial photographs from the year 1996 cover all the area except section No. 4[*]. Therefore in examples section No. 4 is excluded. The total production capacity of all Estonian oil shale open casts is 3 million m3 or 5 million tonnes of oil shale per year. Every mine produces, on average, 1 million m3 of oil shale per year. Oil shale yield is 3.4 tonnes per m2 of mined area; therefore, the total area of surface mining movement is 1.5 million m2 per year. As could be seen from the chart of the mined areas in the Sirgala open cast throughout its history (Fig. 3), its total annual movement area is 1 million m2. In the case of average rates the area should be around 0.5 million m2. In reality Sirgala’s load is 44 per cent of all open casts. This situation reflects either an overestimated yield of oil shale or oil shale overproduction. Figure 3 Stripping areas of Sirgala open cast from 1949 to 1999, thousands m2 per year Taking 80 m per year for an average shift of the mine face, the total length of operating sections is 20 km. On average, every open cast has a 6.5-km mining front, four mining sections with the length of 1.6 km and four haulage trenches. The width of the mining and haulage trenches varies from 25 to 55 m. The total height of the spoil forms after stripping and reclamation. Mined out oil shale bed with a thickness from 2.5 to 3 m also decreases the final height of the spoil by its thickness. Blasted overburden that consists of lime- and dolostone with clay requires 1.4 times more space than in the bank. The average loosening coefficient of quaternary sediments such as sand, peat, clay and moraine is 1.2. It means that the final height of the spoil surface in the Aidu open cast (see Fig. 1), where the total overburden thickness is 17 and the soft part of it 3 m, will be 4 m higher than the ground surface. In the Sirgala open cast the raise will be 4 m and in the Narva open cast 6 m. The height of the spoils of the overburden material is 3 m higher beside haulage trenches because of the additional material from the trench. The relative change in the surface height in other Estonian surface oil shale mines does not exceed 1 m. These mines are Kohtla, Kohtla-Vanaküla and northern section No. 4 of the Narva open cast. Possible surface mines like Tammiku-Kose, Sonda, Ubja and partly Aidu section No. 2 have the same parameters. For example, in the Kohtla open cast, in the beginning where the overburden thickness is less the spoil height is one metre lower, and after ten years the stripped spoil will be 1 m higher than the original ground. The data from the digital map of the Sirgala open cast show a constant increase in the overburden thickness. Weighted average of thickness of all sections show a constant increase from 6 m in 1950 to 9 m in 1962. Since 1963 till 1978 the thickness increased from 9 to 12 m varying from 6.5 to 16 m. Today the average thickness is 17 m, varying from 15 to 20 m. The overburden material thickness influences directly the future landscape but it also sets limits to stripping equipment parameters and productivity. Stripping capacities (Fig. 4) are therefore influenced by production demand, over-burden thickness and equipment capacities. The graph shows the amount and dynamics of casting overburden material in the Sirgala mine area. Figure 4 Stripping volumes in Sirgala open cast, thousands m2 per year From the beginning of mining, the area of a mine is influenced by haulage trenches. On average two trenches are excavated for every section. They follow the depth of the oil shale bed and are used for mineral haulage and process maintenance. Trenches will be open to the air for the rest of the lifetime of an open cast. They are the most changed elements of the landscape after mining. The area of open casts will be flooded. The depth and width of the trenches are greater than those of most of Estonian natural lakes or rivers. The surface area of the bottom of trenches is 1 ha per 400 m or 2.5 ha per 1 km. The average length of trenches in Estonian open casts is 5 km that makes their average area 12 ha. The relative depth of trenches varies from 8 to 38 m. Comparing to the lakes it equals the water depth in the Estonia’s deepest lake Rõuge Suurjärv. Question is, what the maximum water table height in trenches could be. The water table level depends on the level of water table in the Narva River that is 24 m above the sea level. The surface height of the mining area is 30 m above the sea level, and the minimum height of the bottom of oil shale bed equals the sea level. Due to this the depth of water in trenches will be up to 24 m. In the case of coagulation, the depth of water could reach 25 m or even more. The Sirgala open cast area has 18 such trenches. In practice, abandoned Maardu phosphate rock open cast is a good example of flooded trenches and reclaimed area. Although the overburden materials of these two mined minerals are different, the general view will be the same. The Maardu open cast abandoned in 1991 is surrounded by water channels with a width of 80 to 120 m and water depth of about 3 m. The angle of the trench walls is 35 to 40? like in the oil shale area. When trenches will be flooded in Sirgala and in other oil shale open casts, their water surface area will be 1.5 to 3 times greater than the present haulage road area. In surrounding and deeper trenches the width of the water table in channels could reach 150 m. However, the fact of their existing there causes another remarkable situation. Like in the Maardu mine area today, the channels will surround the reclaimed area and limit the accessibility of the area by transport facilities, which means less human impact on large afforested areas. From the point of view of environmental protection this will be one of favourable influences of surface mining on large and also remote areas. Another similarity with the Maardu mine concerns saving mining process data. Today only few maps and documents are available about the Maardu mine. Mapping its underground part is almost impossible due to the lack of map and other information, caused by changes in the enterprise ownership. The same situation could easily happen to oil shale industry. This brings out another aspects of the importance of the present study - saving information in an easily accessible form for the future. The present open cast landscapes could be divided into four classes (Fig. 5).The first one is the afforested (mainly with pines) area. The second one is the area with poor vegetation, small trees and bushes, fifty per cent of it being a rocky surface. Aerial photographs show it as a striped area. The third one is a graded area, mainly without vegetation but ready for planting. The fourth area has spoils that are not graded and have no vegetation, their surface angles reaching the angle of the repose, maximum 45?. In the presented aerial photograph one-year stripping equals to 1-3 trenches (Fig. 6). Figure 5 Reclamation dynamics of Sirgala open cast area Oil shale surface mining has influenced northeastern Estonian landscape since the first days of oil shale industry. From 1916 to 1927 handwork was used for stripping [3]. Due to this the material of spoils was fine enough for reclaiming, and today this area is afforested or urbanized. Depending on the technology, depth of oil shale bed and political circumstances [3-6], the landscape and surface material varies slightly (the Table). Which of these stages has been best for recovering the nature, is a question for ecologists. Fig. 6. Sharp spoils in the Sirgala open cast In surface mines the same range of equipment is used for stripping low-bedded deposits as for construction, amelioration and agriculture. The maximum reach of construction excavators is usually 6 m; the height of the blasted rock bench can be 1.5 of the excavator reach. This limits the oil shale mining area where such technology could be used to the bedding depth from 2 to 10 m. This 10-metres-limit was reached in the Viivikonna[*] open cast in 1967 and in the Sirgala in 1970. In the Narva mine the mining started in 1970 in the depth of 18 to 19 m, and in 1992 in the northern section - in the depth of 6 to 7 m. In the Aidu open cast, half of section No. 2 (stopped today) has the overburden thickness below 10 m, which could be compared to the present situation in the Narva open cast. Conclusion Oil shale surface mining forms 1/3 of 10.5 million m3 of minerals excavated yearly in Estonia. The Sirgala open cast produces 44 per cent of the surface-mined oil shale. Due to its large area, average mining conditions and remarkable production capacity Sirgala is the best example for illustrating the method of open cast mining, post-mining processes and landscape formed in the oil shale surface mining area. The present study describes creating a digital map of oil shale surface mining technology and evaluating mining influences on the landscape. The data from the digital map of the Sirgala open cast show a constant increase in the overburden thickness. Overburden material thickness influences directly the future landscape but it also sets limits to stripping equipment parameters and productivity. Stripping capacities are therefore influenced by production demand, overburden thickness and equipment capacities. Reclamation technology has reached a nature-friendly level and causes no harm, except trenches, to the landscape. Trenches are the most changed elements of the landscape after mining. Their depth and parameters are greater than those of most of Estonian natural lakes or rivers. Their depth of water could reach 24 m. Oil shale mines, due to shale thin horizontal bedding require special reclamation after their exhausting. The present open cast landscapes could be divided into four classes: afforested area; area with poor vegetation; graded area; spoils. Another aspect of the present study is saving information in an easily accessible form for the future. For this purpose GIS for mining is used. This study is a part of the development plan of Ida-Viru County and Estonian Oil Shale Company. Acknowledgements This study was supported by Estonian Science Foundation (Grant No. G3403) and by support 0141321s99 for postgraduate studies at Tallinn Technical University. REFERENCES 1. Valgma, I. Mapping potential ground subsidence areas of Estonian oil shale deposit // Proc. of Conference on Mining Law and Mining Safety. Tallinn, 1999 [in Estonian]. 2. Valgma, I.Mapping potential areas of ground subsidence in Estonian underground oil shale mining district // Proc. of the 2nd International Conference - Environment. Technology. Resources. Rezekne, Latvia, 1999. 3. Fifty Years of Oil Shale Mining in Estonian SSR / Valgus. – Tallinn, 1968 [in Estonian]. 4. Sirgala 35 / Disantrek. - Tallinn, 1997 [in Estonian]. 5. Work of the Open Cast – Result of the Work of Team and Shift / Valgus. – Tallinn, 1986 [in Russian]. 6. Teetlok, K. Reclamation of Land Disturbed by Mining of Mineral Resources and Their Influence to the Environment of Estonia / Institute of Geography, UT, Tartu, 1995 [in Estonian]. Presented by E. Reinsalu Received March 3, 2000 Fig. 3. Stripping areas of theSirgala open cast from 1949 to 1999, thousands m2 per year Fig. 4. Stripping volumes in the Sirgala open cast, thousands m2 per year Fig. 5. Reclamation dynamics of the Sirgala open cast area [*] Aerial photographs of the eastern zone are missing because of the country border existing there. [*] Viivikonna open cast was joined to Sirgala in 1987. [SLIDES]