Potential usage of underground minewater in heat pumps

Mine water as a potential source of energy from underground mined areas

Mine water as a potential source of energy from underground mined areas in Estonian oil shale deposit

Oil shale mining influence on the environment

Oil shale mining influence on the environment

Environmental impact of mining

Paper: Environmental impact of oil shale mining

Paper: Geotechnical Processes and Soil-Water Movement with Transport of Pollutants

Paper: Geotechnical Processes and Soil-Water Movement with Transport of Pollutants in the Estonian Oil Shale Mining Area



http://www.minest.ee/water
txt: GEOTECHNICAL PROCESSES AND SOIL-WATER MOVEMENT WITH TRANSPORT OF POLLUTANTS IN THE ESTONIAN OIL SHALE MINING AREA Tallinn Technical University, Department of Mining 82, Kopli Str., 10412 Tallinn, Estonia Abstract One of the most important industries of Northeast Estonia is oil shale mining. Ground movements caused by mining reach the ground surface easily due to shallow location of workings. A new, artificial topography is formed on undermined areas, where the ground surface depressions are alternating with rising grounds. When the Quaternary cover contains loamy sediments, the surface water will accumulate in the depressions. The response of usable lands on undermined areas depends on the degree of changes in the relief and water regime. The accumulation of solid residues by oil shale mines and processing plants has resulted in numerous ash hills, which are polluting the environment. The streams are polluted by phenols, oil products and sulphates. The main source of water supply is groundwater in the oil shale basin. The hydrostratigraphic section is represented by three aquifers. Two (Quaternary and Ordovician) of these aquifers are affected by the human activity. Intensive water consumption has caused a fall in the water level in these aquifers. Due to oil shale production the concentration of Ca2+, Mg2+, SO4 2- and Cl contained in the groundwater from the Ordovician deposits is noticeably higher than in the water with a natural background level. The natural water chemical regime is restored at the cessation of mining. Introduction Estonia is situated on the shore of the Gulf of Finland (Fig. 1) and is characterised by flat topography with only slight differences in elevation. Gulf of Finland Estonia Russia 20 kilometers 0 10 Narva Sirgala Estonia Kohtla - Järve ash dumps Kiviõli ash dumps Kohtla-Järve Sompa Tammiku Ahtme Kukruse Viru Sillamäe Mined out area Claims of oil shale mines Ash dumps Oil Shale outcrop ESTONIA LUXEMBOURG IRELAND DENMARK ANDORRA MONACO LIECHTENSTEIN BOSNIA AND HERZEGOVINA FR. YUGO. REPUB. OF MACEDONIA ARMENIA ICELAND LATVIA MOLDOVA LITHUANIA SLOVENIA PORTUGAL NETHERLANDS FRANCE SPAIN FINLAND NORWAY SWEDEN GREECE ROMANIA UKRAINE SLOVAKIA CZECH REPUBLIC POLAND BELARUS RUSSIA GEORGIA MALTA Fig. 1 Location map of Estonian oil shale deposit. Oil shale reserves are concentrated in North-East Estonia (Fig. 1) and make up about 3,8 billion tons, half of which can be mined according to existing technology, economical and ecological criteria. The annually exploitable layers have an average thickness of 2,6 m and the bedding depth increasing in the southern direction. Oil shale consists of 30-40% organic (kerogen) and 60-70% mineral matter (mainly carbonates and sandy-clayey minerals). The sulphur content averages 1,6 %, the net calorific value varies from 6-10 MJ/kg. Oil shale output increased from 2 million tons in 1940 to 31 million t in 1980, and has since decreased to 12 million tons (Fig. 2). 0 5 10 15 20 25 30 35 1920 1940 1960 1980 2000 2020 Output, Mt per year Output Forecast Fig. 2 Estonian oil shale annual production (mining output) and forecast by Enno Reinsalu (Reinsalu, 1998) The study object was of 290 km2 underground and 130 km2 strip mined area (Valgma, 2002). Oil shale is presently excavated in two surface and two underground mines. For excavation oil shale the mines must be dewatering. The mine water pumped up the oil shale underground and surface mines and discharged into rivers forms on the average 86% (quantitatively 159- 226 millions m3 /yr). In the region of oil shale mining on an average 15 million m3 of water is being pumped out of mines monthly (Fig. 3). Mines drainage causes the depletion of ground- 0 5 10 15 20 25 30 35 40 45 January February March April May June July August September October November December million m3/month 1999 2000 2001 2002 Fig. 3 Water, which pumped out of surface and underground mines monthly water, resulting in drawdown of 20 m in the northern and 70 m in the southern part of mining area. The infiltration of contaminants grows and the main aquifers are chemically polluted over a large area. The formation of the chemical composition of water is influenced by considerable variation of hydraulic conductivity, numerous faults in the strata, karst and, in addition, depressions forming during mining. Evidently each singular case represents a plurality of underlying causes and hence a considerable variety of analytical results depending on the location and season of sampling. Methods During years 1998...2001 geotechnical processes of closed underground oil shale mines and opencasts were investigated. A digital map of Estonian oil shale mining was created for joining data of technological, environmental, and social limitations in the deposit. The main objective was the stability of underground mined area. The stability was studied with help of aerial photographs, mine drawings, maps of quaternary sediments and mathematical modelling of rock failure. Water sampling took place during the spring and summer from 1988 to 1990. This period samples were from tectonic faults and karst fissures in mines, and also from pumped public supply or private boreholes. Springs and rivers were also sampled to obtain a reasonably complete hydrochemical understanding of the hydrogeological cycle in this area. The chemical analysis from more than 20 constituents was carried out on water samples from each of the 31 sampling sites. From Eesti Põlevkivi Ltd. and Estonian Geological Survey were received the official data for the period 1991-2002 and these are following: annual amounts of mine waters, chemical content of water, annual influxes of sulphates with mine waters, data of water regime, the chemical content of ash dumps water. Results The main influences of underground mining on the surface are spontaneous collapses and subsidences. Subsided land is located above hand-mined, advancing-and-retreating mining and longwall mining with double-unit-face areas. The relief of subsided land depends on the quantity of the filling material and filling quality, and on roof structure. Information was collected mainly about random spontaneous collapses of drifts and spontaneous collapses of room-and-pillar mining. Some information is collected about induced caving of longwall mining in Kohtla mine. Considering that longwall mining was stopped in the Estonian deposit in the year 2001, the information about induced caving should be collected and analysed as well. The area of subsidence moulds is in average 55600 m2 ranging from 2500 to 152500 m2 in total. There are 3.1 km2 subsidence areas. Some of the spontaneous collapses mentioned by mining surveyors cannot be recognized on the surface and some seen on the surface have not been reported. In these cases the fieldwork was done with GPS device and caving possibilities considered with the help of digital maps. Cavings have been found in the areas where mines operated within the period of 1963...1989. Surface mining mapping included digitising haulage and mining trenches, loading points, dewatering constructions like ditches, basins and tunnels. Besides, yearly mining ranges were digitised. Created database includes geological characteristics and data of the used technology. Map of yearly mining ranges offers a good overview of the mining period, speed and extent. The present open-cast landscapes can be divided into four classes. 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. 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 are reaching the angle of the repose, maximum 45o. One year stripping equals 1-3 trenches. As an example, the former Narva open-cast has been modelled. Digital elevation model (DEM) was created from geological, topological and mining data. There are two principal types of spoils in open cast mined areas. First is formed by beginning mining technology in 1925 to 1950. Oil shale layers were mined by handwork and overburden was stripped by 3 m3 steam excavator in cooperation with spreader. The width of the mining pit was 20 m, forming spoils with maximum slopes 20o. The thickness of the oil shale layer was 2.6 m and the overburden thickness varied from 5 to 12 m. Average stripping factor was 1.9 m3 t-1. Due to this, average height of the ground in the mined out area is from 0 to 2 m below original ground surface, forming deeper and higher peaks. Depending on that, the moisture content of spoil might be higher than that of the soil in the same area before mining. Since spreader and mechanical shovel were used for stripping, the estimated swell factor of the material was 1.3. Maximum size of the material could be 1.4 m due to bucket size and average size was 150 mm. Because of low mobility of the spreader and missing reclamation requirements, the unevenness of the spoil varies between 0.5 and 2 m. The content of organic matter in the spoil, originating from kukersite oil shale, is on average 4%–6%. That material is evenly spaced in the spoils due to stripping method. The second type is mined with newer technology beginning from 1950ties. The area was mainly covered with swampy forests and bogs. Oil shale layers were mined by blasting and overburden was blasted and stripped by 15 m3 and 90 m long boom draglines. The width of the mining pit was 50 m, forming spoils with maximum slopes 3o. The thickness of the oil shale layer was 2.0 m and the overburden thickness varied from 11 to 17 m. Average stripping factor was 4.1 m3 t-1. Due to this, average height of the ground in the mined out area is about 2 to 4 m above the original ground surface. Depending on higher surface than natural and water pumping due to operating open cast, the moisture content and seepage of the spoil might be lower than in the first area. Organic part of the left oil shale layers is mostly in bottom. Dragline and in some cases mechanical shovel were used for stripping of blasted overburden rock, therefore the swell factor of the material was 1.4. Maximum size of the material is 3.1 m due to bucket size and average size was 300 mm. Unevenness of the spoil ranges from 0.5 to 1.5 m on average, but it can be up to 6 m in test sections. The content of organic matter in the structure of spoils, originating from kukersite oil shale, is on average 2% being 4% in bottom and 1% in surface of the spoil. Due to stripping method the material is unevenly spaced in the spoils, the estimated swell factor is up to 1.5 in the bottom. This is another reason for water runoff from the spoils. Because of several mines are being closed during next few years the problems of drowned waste are going to be more actual than before: increase of underground water level, underground water pollution, technogenic water sources and over flooding of reclaimed areas. The chemical analyses of groundwater divide into two principal groups (Fig. 4): - a very large group of CaHCO3 waters; - a large group of Mg(Ca)SO4(HCO3) waters. 0 100 200 300 400 500 600 700 mg/l underlying 7 4 67 17 309 10 10 overlying 10 9 59 30 356 10 9 closed mine (Tammiku, Sompa, Kukruse, Ahtme) 30 7 181 47 385 370 36 working mines (Estonia, Viru) 20 10 156 50 427 620 57 surface mines (Sirgala, Narva) 12 8 174 55 353 530 35 Na K Ca Mg HCO3 SO4 Cl Figure 4. Chemical compositions of groundwater and mining water The influence of groundwater consumption, dewatering of surface and underground mines on the groundwater regime was evident. In the course of oil shale mining at the Estonian oil shale deposit three stages of Ordovician aquifer system have been partially or totally drained. The observation data show that all the aquifers are interconnected and oil shale mining exerts a remarkable influence on all of them. Contamination in this region is mostly due to pollution caused by power and chemical industries. Studies of ash hills demonstrate that the ash may be highly enriched in certain potentially toxic elements, typically semi-volatiles, such as boron, arsenic, antimony etc. The ash dumps water (Table 1) is typically rich in oxides and may have an extremely high (alkaline) pH, which may render some metallic or semi-metallic species highly mobile. Table 1. The composition of the ash dumps water Content, g/m3 Pollutants Interval Maximum Chemical oxygen demand (COD) 4000-8000 18000 Biochemical oxygen demand (BOD) 2500-4000 6400 Phenols 200-580 1400 Volatile phenols 80-110 150 Oil products 30-70 100 Benzo(a)pyrene, g kg-1 0.05-0.15 0.22 Sulphides 100-230 270 Dry matter 3500-6000 7300 Suspended solids 300-600 1300 Total hardness, eqv m-3 30-47 53 pH 11.4-12.2 12.5 There is increasing evidence that portions of the water infiltrating through the soil surface may move rapidly through the aeration zone along preferred flow paths such as macropores and fractures. This rapid, concentrated flow may also have significant implications for the transport of pollutants to the groundwater body. Discharge into the macropores and the concentrated groundwater recharge in the vicinity of the macropores occurred in relation to the development of the groundwater mound. Incorporation of the soil-water movement would bring better prediction of the time, location and magnitude of groundwater pollution due to the transport of pollutants by the infiltrating water. Discussion The basic processes that determine the chemical composition of water in the samples can be classified as follows: - chemical composition of water in the structurally undamaged aquifers; - chemical processes taking place in the sites of tectonic damage and erosion; - infiltration of groundwater (atmospheric precipitations and extracted water) through loading layers; - man-made changes in the environment. As a result of the combined influence of these processes the natural bicarbonate-type water, characteristic of the Ordovician aquifer of the given region, has changed into sulphate- bicarbonate water, having increased from 0,2...0,3 g to 1,0 g/l. Essential role in the formation of the chemical composition of water, especially in shaping local singularities, is played by tectonic damages and karst; in that case the value of the hydraulic conductivity increases. In the regions where tectonic faults are widespread general mineralization may be twice as high as that usually characteristic of water aquifer. Concentrations of Na+ , Ca2+ and Cl are also much higher. Very significant part in the formation of the chemical composition of waters is played by depressions that have sprung up in the course of mining. Their impact is two-hold: infiltration and water exchange increase significantly and with the alteration of aeration conditions a geochemical environment with new physical-chemical properties is formed. Conclusions Natural hydrogeological conditions in Northeast Estonia were simple, but they have been disturbed by the mining industry and consumption of the groundwater. Deeply fractured carbonates, together with effects of mining, have facilitated the rapid spread of aquatic pollution. Mineralised mine water extraction is useless, and the reduction of its mineralization level by technological means or natural filter systems is a problem which needs tackling in the near future. Today this water is guided to natural water bodies. As the content of sulphates in mining waters is high, the concentration of sulphates in the bottom sediments of many water bodies has risen sharply. Due to strong eutrophication there is an oxygen deficiency in some places and the reduction of sulphates to toxic H2S already occurs. The study was supported by EstSF GRANTs G3403 and G4870. Bibliography 1. Reinsalu, E. Is Estonian oil shale beneficial in future? Oil Shale, 15/2, 1998, 97-101. 2. Valgma, I. Estonian oil shale resources calculated by GIS-method. Symposium on Oil Shale., Tallinn, Estonia, 18-21 November 2002

Possibilities of mining under the mire

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. Koitmets K, Reinsalu E, Valgma I (2003) Precision of oil shale energy rating and oil shale resources. Oil Shale 20(1):15–24 14. Loopmann A (1996) Formation, development and perishing of mire massis. Development of mires and formation of bed­pool complex. J Estonian Peat 3(4):18–21 [in Estonian, with English summary] 15. Lu W, Luo Y, Chen M et al (2012) An introduction to Chinese safety regulations for blasting vibration. Environ Earth Sci 67(7):1951–1959. doi:10.1007/s12665­012­1636­9 CrossRef 16. Mining­law and legal regulation acts (1998) Ministry of Environment, Ministry of Economy. Part II, Tallinn, (in Estonian) 17. Nestor H, Soesoo A, Linna A, Hints O, Nõlvak J (2007) Ordovician in Estonia and southern Finland. MTÜ GEOGuide Baltoscandia, Tallinn, pp 1–32 18. Niinemets E, Pensa M, Charman D (2011) Analysis of fossil testate amoebae along the hummock­lawn­hollow gradient in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. 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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Paper: Technologies for Decreasing Mining Losses

txt: Environmental and Climate Technologies _________________________________________________________________________________________________2013 / 11 41 doi: 10.2478/rtuect-2013-0006 Technologies for Decreasing Mining Losses Ingo Valgma , Vivika Väizene1 , Margit Kolats1 Tallinn University of Technology Abstract - In case of stratified deposits like oil shale deposit in Estonia, mining losses depend on mining technologies. Current research focuses on extraction and separation possibilities of mineral resources. Selective mining, selective crushing and separation tests have been performed, showing possibilities of decreasing mining losses. Rock crushing and screening process simulations were used for optimizing rock fractions. In addition mine backfilling, fine separation, and optimized drilling and blasting have been analyzed. All tested methods show potential and depend on mineral usage. Usage in addition depends on the utilization technology. The questions like stability of the material flow and influences of the quality fluctuations to the final yield are raised. Keywords – oil shale, losses, mining, extraction. I. INTRODUCTION In case of stratified deposits like oil shale deposit in Estonia, mining losses depend on mining technologies. Stratified deposits are being developed from lower bedding depth to deeper and more complicated conditions [23]. Continuously the environmental or social restrictions require increasing coefficients that increase mineral losses [20]. This could be limited with the help of technological development [34,13, 36]. During the period starting from 1916 many technologies have been used and tested [31]. Currently the market economy is the main driving force for choosing technologies. This causes short term choices and works against sustainability. Current research focuses on extraction and separation possibilities of oil shale. Selective mining, selective crushing and separation tests have been performed, showing possibilities of decreasing mining losses. Rock crushing and screening process simulations were used for optimizing fractions. In addition mine backfilling, fine separation of oil shale, and optimized drilling and blasting have been analyzed. All tested methods show potential and depend on mineral usage [37]. Usage also depends on the utilization technology. Questions like stability of the material flow and influences of the quality fluctuations to the final yield are raised. Tonnage, calorific value and size distribution of the product form the quality indicators [43]. Avoiding losses in any of these processes decreases mining losses and has a positive effect on resource usage and sustainability. In addition, decreasing losses increases the amount of resource and sustainability of energy supply for the country [30, 32]. If optimized technology allows maintaining required productivity, it could be applied, even if fitting into the existing technological structure is taking longer than technically available [33, 35, 8]. The aim of the current study is to clarify what technical solutions could be applied for decreasing oil shale mining related losses. II.ANALYSES AND TESTS A. Selective mining Selective extraction of oil shale seam was analyzed to understand following methods: 1. Cutting with bulldozer and excavator rippers 2. Cutting with surface miners 3. Cutting with longwall miners 4. Cutting with shortwall miners. a) Cutting with rippers Selective extraction of the oil shale seam can be done by a bulldozer ripper or hydraulic excavator ripper. Ripping is a low-selective technology [42]. In deeper surface mining areas, 100 tonnes class bulldozers were used and in more weathered areas or partial ripping zones, the 60 tonne class was used. One disadvantage of bulldozer ripping is excessive crushing of oil shale by heavy bulldozers with crawlers [18]. b) Cutting with surface miners Tests with surface miners Vermeer T1255 and Wirtgen 2500 SM were carried out. The tests were followed after longer period tests with smaller class surface miners during the last 25 years. Tests have been performed with different oil shale and limestone layers. Surface miners are considered as BAT (Best Available Technology) for surface oil shale mining extraction [12, 42, 18, 15, 5]. c) Cutting with longwall miners The planning and testing has been done for longwall mining possibilities. Shearers were used and tested for 30 years in five oil shale mines in Estonia [1]. Longwall technology has also been chosen as one of the alternatives for phosphate rock mining [41]. Technologically, this technological solution has improved compared with initial possibilities. Since the hydraulic support system was limiting the height of the longwall face (1,5 m) and the power of the shearers was relatively low (210 kW) the losses have been 50% in longwall section. Today’s sharers utilize power in the range of 2200 kW, which is 10 times higher than in the tested units. Since the productivity (equal to income) could be increased, longwall technology is one of the possibilities for lowering losses. In case of removing protective side pillars between longwall section, rough estimation shows, that losses could be lowered down to 5% taking into account the geological dislocations and disfollowing the exact horizontal plane of the oil shale seam. The main obstacle of longwall shearing Brought to you by | Tallinn Technical Authenticated | 193.40.249.178 Download Date | 10/17/13 10:07 AM Environmental and Climate Technologies 2013 / 11_________________________________________________________________________________________________ 42 technology is solving environmental and social questions, regarding subsiding the ground and accepting certain areas where such subsiding could be allowed. In comparison to the surface mining stripping in the open cast mining areas, longwall mining could be considered as a technology which causes less impact to the landscape. The ground would be lowered by up to 70% of the created space. That makes 2 meters. In open casts, even the fluctuations in the leveled overburden spoil could be 5 meters. In trench or ditches areas, the level fluctuations are up to 40 meters. This makes longwall mining the most sustainable mining method for oil shale. d) Cutting with shortwall miners Evaluations of breakability have been made with roadheaders F2 and 4PP-3. As a recommendation, a doubledrum road header was proposed. Currently the power of the machines has increased and pick properties allow cutting harder rock. It is proposed, that both longitudinal or transverse head continuous miners (roadheaders) could be used for cutting oil shale [12]. The selectivity option is directly related to the waste material handling and should be tested in the mine [11]. Shortwall miner utilization could be the solution for making development entrances, drifts and rooms for mining. In case of satisfactory cutting performance, it could be used for extracting oil shale in production sections as well. The tests have shown, that shortwall mining is a promising technology and requires, as with longwall mining, surface miner mining and axle bucket crushing changes in some operations and processes in mining technology. Shortwall mining requires fast roof supporting technology. The supporting could be in addition in some extent easer because of lower possible fragmentation of rock caused by absence of blasting in the mine. B. Selective crushing For selective crushing, the following methods were tested: 1. crushing in a drum (Bradford drum) with help of rock falling impact and hammer crusher inside the drum; 2. impact crusher in underground sections as first stage crusher or impact crusher for aggregate production from oil shale waste rock; 3. axle crusher buckets with cutting and skimming process. An impact crusher has been used in underground sections as a first stage crusher and for aggregate production from oil shale waste rock that is limestone [27]. The purpose of underground crushing is to reduce ROM (run of mine) size to the required size of up to 300 mm for transporting it on belt conveyors to the surface. C. Separation Separation tests have been performed by jigging and cycloning. The purpose was to find out the percentage of the fine material that could be separated. Jigging tests have shown relatively good results allowing separating initially mixed material into five different fractions. The calorific value of best fraction is highest and the limestone fraction in opposition should be considered as the ready selected material for limestone aggregate. Up to now the main focus has been mechanical experimenting with jig. The main obstacle of the technology could be achieving required productivity. It is similar to the filter press technology where the productivity of the single unit could be low. On the other hand, if the production line could be completed with different stages, the required productivity could also be to some extent lower. To decrease required machine productivity for the same output, drum crushing or axle crushing could be used prior to the jigging. Cycloning has shown that the calorific value of cycloned and non- cycloned fine material has no remarkable difference. Since cycloning could be done on many variations, the initial test could be considered as failed because of short time and no variations. These tests should be continued, preferably with apilot unit or laboratory units at first. D. Rock crushing For crushing, the following options have been analysed: 1. Crushing with sizers 2. Crushing with impact crushers 3. Crushing with double drum crushers 4. Crushing with drum crusher 5. Crushing with jaw crusher. Crushing process simulations were used to evaluate the distribution curves of the final product. The necessary data for this purpose is bulk density of material and the maximum size of the particles going for crushing. In order to get optimal results on certain cases, crushing units, crushers and mobile crushers can be added to the scheme. This gives extra value in lowering engineering costs, on experimenting with different devices and on further changes [19, 45]. As an example, material data for thesimulation program has been:  Input material < 1000 mm  Solid density 1,84 t/m3  Crushability 85% - which is the maximum  Productivity 1000 t/h  Gravel 31% - does not influence the results (Fig. 1.). The value of abrasiveness has been between 0,1…1500 g/t, calculations show that this does not affect the simulation results. Neither does moisture. The crusher output cavity is set on 180mm which means that the maximum size of the outcoming particle is 200mm. The workload of the impactor crusher is 97% of the maximum capacity. After crushing, the feed moves to the roller screen, where the feed flows into three classes:  0…25 mm 22,8%  12…107 mm 55,2% - which include 11% 12…25 mm (Fig.2.)  107…200 mm 22% . It can be detected that the fines part is 28,9%. Brought to you by | Tallinn Technical Authenticated | 193.40.249.178 Download Date | 10/17/13 10:07 AM Environmental and Climate Technologies _________________________________________________________________________________________________2013 / 11 43 Fig. 1. Material data insertion window Fig. 2. Flow data Fines are added on the secondary crushing/particle size is 107...200 mm. Calculations have shown that in this way 5% of fines are added. At the present moment the best crushing option in making the minimum fines is crushing with the sizer. Experiments show that the minimum in generating fines is achieved when the rotating speed of sizer was 175 rpm. In slow rotation the generation was 11,8% and fast rotation gave 6,5% of fines (Fig.3). As experiments show, it is possible to decrease the fines generation which mostly is considered to be waste. Each simulation manufacturer focuses on separation methods or some part in the separation process. When it comes to crushers, then simulations are also manufacturer based and reflect types and models, what the company offers [7, 4]. Newer products are introduced in the simulation programmes later. In case of the roll crusher for example, the characteristics and behaviours are still added to the programme. Sizers are even more complex, because they have been used only a few years and therefore are relatively new products among crushers. In Estonia there are a lot of questions concerning the fines in the crushing process. Fig. 1. Experiments resulted in fines generation of 2,2% [10] E. screening Two basic screening solutions have been analysed in addition to the traditional vibration screening: 1. Screening in drum screen 2. Screening on rotary screen 3. Screening on roller screen. F. Mine backfilling The tests contained testing of mixes properties of the backfill material, testing of backfilling technology and analyzing backfilling material flows. The main hypotheses are that backfilling reduces mining losses and the amount of waste on the ground surface [27]. In addition it increases land stability [12]. Stability issues have been developed in sense of information availability. Mapping, special information systems and seismological methods allow one to detect any collapses which have occured [21, 25]. G. Fine separation Fine separation tests were carried out with CDE equipment and with jigging equipment. The aim of the fine separation test is to separate fines from pulp before they reach sedimentation pond and to take it into use as a product. III. RESULTS AND DISCUSSION A. Selective mining a) Cutting with rippers In Ubja oil shale open cast, the productivity of oil shale hydraulic ripping was nearly 600 m3/h. At the Ubja open cast, overall oil shale losses are 0% based on the Environmental Register. Bulldozer ripping is considered as semi-selective ripping where seam losses make 12% in comparison to 5% with surface miners [42]. The first problem of ripping technology has been power of ripping machines. Before 100 tonnes class bulldozers were applied, the low ripping power was one of the main concerns. Excavator ripping is in similar stage like bulldozer ripping has been in its beginning stage. The power of the excavator ripper is not satisfactory to reach required productivity. Excavator ripping does not solve the losses question because of the principle of vertical movement. Brought to you by | Tallinn Technical Authenticated | 193.40.249.178 Download Date | 10/17/13 10:07 AM Environmental and Climate Technologies 2013 / 11_________________________________________________________________________________________________ 44 Excavator ripping could be considered in low bedding areas, where drilling and blasting is prohibited, the oil shale seam is weathered meaning weaker bonds between layers. A bulldozer ripper, therefore could be used as low selective miner, but it is limited by availability of keeping losses down. The main problem is limestone and oil shale pieces and lumps that contain both material and could not be separated by the ripper. If needed, one of the solutions could be skimming with axle crushers. b) Cutting with surface miners It was found that extracting with a high selective surface miner is the main possibility of decreasing losses in case of surface mining. The main obstacle for using such technology is the partly unsolved overburden stripping technology. In the future, combined methods should be considered like high selective cutting plus selective axle crushing for aggregate separation. Mining with surface miner Wirtgen 2500 SM helps to reduce losses and improve calorific value of oil shale. It is possible to mine limestone and oil shale seams separately with higher accuracy than rippers (2-7 cm) with deviations about one centimetre [42]. Losses can be decreased from 12 percent to 5 percent compared to ripping [18]. Based on practical data, the surface miner enables to increase the output of oil shale up to 1 tonne per square meter. The oil yield increases 30%, reaching up to 1 barrel per tonne of oil shale during the oil shale retorting, because of better quality, meaning higher calorific value of the material that is sent to the retorts [42]. c) Cutting with longwall miners It was found that distribution of required large particles of oil shale is possible with longwall shearers. The practice with longwall shearers shows that the subject for cutting is oil shale and the larger size is distributed to the limestone fraction [1]. This is due to the hardness difference of the rocks. Longwall mining could decrease horizontal losses by 20 to 40%. d) Cutting with shortwall miners One of the main advantages that a shortwall miner could present are the possibility of avoiding weakening pillars in the mine by blasting [20]. This in addition could give the possibility to decrease pillar size and to decrease losses left to the pillars. Pillar losses that are caused by pillars with cross section area of 16 to 49 square meters could be decreased therefore by 16 to 28% with avoidance of the 0,3 zone by sides of the pillars. The pillas strength and stability of the ground are directly related but have the opposite influence on sustainability. In case of backfilling this dilemma could be solved [22]. In some areas also smooth and directed subsidence could be solution. B. Selective crushing The underground crushing process where ROM (run of mine) size is reduced to the required size up to 300 mm has no direct influence on the percentage of losses. Nevertheless, ROM size distribution is influenced by impact crushing and fines are produced. In case of oil production with vertical generators, fines and small classes of oil shale are considered as waste, if no other uses are found, like cement, electricity or oil production with SHC technology. Selective crushing is important both for cleaning and sizing oil shale and cleaning and sizing limestone. Therefore selective crushing or selective mining methods are recommended [27]. C. Rock crushing a) Crushing with sizers One of the options could be using slow rotating or optimized rotating sizer for oil shale ROM crushing. According to the recommendations of crusher producers, all crusher types are suitable for crushing oil shale [25]. In relation to the moisture content, jaw crusher and gyratory crushers are unsuitable, requiring relatively dry material (

Influence of water discharging on water balance and quality in the Toolse river in Ubja oil shale mining region

Paper: Influence of water discharging on water balance and quality in the Toolse river in Ubja oil shale mining region

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: The impact of infiltration dam on the ground water regime

Paper: The impact of infiltration dam on the ground water regime in the Kurtna Landscape Reserve area



txt: Oil Shale, 2006, Vol. 23, No. 1 ISSN 0208-189X pp. 3–14 © 2006 Estonian Academy Publishers THE IMPACT OF INFILTRATION DAM ON THE GROUNDWATER REGIME IN THE KURTNA LANDSCAPE RESERVE AREA Mining Department of Tallinn University of Technology Ehitajate tee 5, 19086 Tallinn, Estonia The area of Kurtna Landscape Reserve is situated between oil shale mines. This area is an important part of the Estonia deposit, and the located mining conditions there are good. Narva surface mine pumps groundwater from the area of Kurtna Lakes. It is able to minimize the influence of surface mining. Testing of mining technology and hydrogeological modelling show that mine front may be closed for stopping water flow instead of leaving an open trench by the border of the area of the lakes. According to modeling, hydraulic conductivity of the dam must remain 0.1 m/d to avoid sinking of water level in the lakes, and filtration basins must be supplied with water in an amount of 7000 m3 /d as yearly average. As the result, the landscape will be reclaimed, overall look and shape will be smoothed. Abandoned fields of peat milling will be reclaimed, and their fires will be avoided. Introduction The influence of the power and mining industry on Kurtna Lakes located in the centre of the oil shale mining area in North-East Estonia has been a discussion object for the last fifteen years. Oil shale mines surround the area of Kurtna Lakes. There are 40 lakes in a 30-km2 area above a 70-m deep buried valley [1]. Two mines – Estonia and Narva – exert the greatest influence on this. Both mines pump out water from the area and lead it back to the lakes or rivers in the same area. The question is how much the mining influences protected lakes and species. Besides Narva surface mine neighbouring the lakes has claimed the permission to pump groundwater from the lake area (see Fig. 1). Surface mining was stopped at a distance of 2 km from the protected area since the problem had not been solved, thus the mining company asked independent research groups to perform corresponding analyses and to test the mining technology used in this area. * Corresponding author: e-mail ingoval@cc.ttu.ee 4 I. Valgma, H. Torn, K. Erg Fig. 1. Location of the Kurtna Landscape Reserve, mining section and infiltration dam There are two main reasons for mining oil shale in the area. The first reason is oil shale resource. Local reserves represent an important part of the Estonia Oil Shale Deposit [2]. Energy rating of oil shale is one of the best among the potential mining areas reaching 44 GJ/m2 , and depth is relatively low (10 to 15 m) compared to 22 m in the rest part of the surface mining area [3, 4]. This resource is of great economical importance because when mined, total costs of mining will remain stable. On the other hand, pressure on mining oil shale in unsuitable areas will become actual in the future [5]. From these aspects, the application for mining permit is reasoned. Since Estonian main oil shale-fired power plant has been renovated, and new boilers require oil shale of a more stable quality than the former ones, the need for oil shale mining remains actual for at least 25 years, which corresponds to the resource in current minefields [6]. New power units operate applying a new, fluidised-bed technology that guarantees less impact on the environment. Total resources of oil shale in the Estonia deposit guarantee operating of power plants for 60 years [2, 5]. Due to low oil shale quality in the most part of the deposit and additional environmental restrictions, the quantity of mineable oil shale is not as great as it seems. Compared to 50% total loss of oil shale resource in the case of underground room-and-pillar mining, the loss in open cast mines reaches 30% [7]. The losses are due to differences in official and actual resources and oil The Impact of Infiltration Dam on the Groundwater Regime in the Kurtna Landscape Reserve Area 5 shale remaining in supporting, protective and barrier pillars. As for the usage of resources, surface mines are more valuable [8]. The main problems concerning mining fields are related to mining conditions and environmental restrictions. Surface mining is reaching depth limit, while underground mining is confronted by low quality of oil shale, bad roof conditions and environmental restrictions [4, 9]. For these reasons continuation of mining in the section neighbouring the area of Kurtna Landscape Reserve is advisable. Mining in the test section should be performed under continuous monitoring for calibrating dynamic modelling with groundwater software. Influence of oil shale mining on the area of Kurtna Landscape Reserve The influence of mining on the lakes has been investigated from the hydrogeological aspect, recommending the usage of infiltration basins and regulation of water flow [10–14]. Water chemistry has been investigated proceeding from the effect of oil shale mining on sulphate content of water [15]. The influence on the landscape and plants has been studied by analysing plant species and mining waste [16–19]. The set of water wells and lakes in the water monitoring program has been set to analyse changes in ecological situation. Unfortunately, it has not given a clear answer to the question about the influence of mining on the groundwater flow in the area. The reason for that has probably been complexity of situations and lack of an interested party who would evaluate all the aspects concerning this region. The closest lakes (Kastjärv, Aknajärv, Jaala, Kihljärv, Nootjärv, Valgejärv and Virtsiku) are located in a distance 1.5 to 3 km from the front of Narva surface mine. Data of observation wells show that the level has not been remarkably changed due to surface mining operation during the last five years. All these lakes are located in the area of boggy, glaciolacustrine and -fluvial deposits. Drawdown of groundwater has been formed due to an intensive consumption of groundwater at the water intake in the central part of the Vasavere buried valley. Quaternary aquifer is an unconfined waterbearing stratum. The values of porosity and permeability of Quaternary aquifer depend to a large extent upon the degree of sand cementation. Consequently, these values are generally expected to be much higher for the central part of the valley than for the slopes. A study of the samples shows that porosity values exceeding 33% are common for the central part, whereas those less than 20% are usual for the southern part of the valley. Similarly, intergranular permeabilities average 2500–2700 m3 d–1m–2 in the central part and drop to 10–50 m3 d–1m–2 at the border of the valley [20]. Seasonal factors, changing flow and various forms of recharge may all produce fluctuations in the water level of about 1 m. 6 I. Valgma, H. Torn, K. Erg 32 33 34 35 36 37 38 39 40 1999 2000 2001 2002 2003 2004 Water level, m Fig. 2. Sinking of water level shows sand inflow to the trench and quick normalisation of the state after closing the flow. Water wells B 6-1 ja B 6-2 are located between Lake Kastjärv and the dam Fig. 3. Technogenic valley formed after sand flow into the trench in March 1999 Water table of L. Valgejärv lowered 2 m in 1984, caused by water usage for stopping peat fires. For the year 1996, water level was normalised again. Only one remarkable event happened in 1999 when sand basement of the peat field flew into mining trench (see Fig. 2, 3). This happened because the spoil was piled on ice, and when ice melted sand spoil became unstable. The water-table diagram shows that original water level was restored quickly after closing sand inflow. The Impact of Infiltration Dam on the Groundwater Regime in the Kurtna Landscape Reserve Area 7 Mining technology The influence of Narva surface mine at the east side of the lakes’ area could be minimised. First, the mine front can be closed for stopping water flow instead of leaving an open trench in the border the area of lakes. Second, the overburden material that is used for closing the trench can be piled in such a way that it has lower permeability than soil in the nature. Besides, a part of that area is covered with abandoned fields of peat milling. Thickness of the residual peat layer reaches up to 3 m being a good material for decreasing permeability of the final dam material. For testing these assumptions, a test section was planned and designed by Mining Department of Tallinn University of Technology in 1997. The purpose was to test whether the filtration dam will decrease the sinking of water level in the area. Test mining in this section started in 1998. The idea originated from dam-piling experiences in the same mine where a dam has been piled with careful dumping and mixing of overburden material (see Fig. 4). This resulted in accumulation of water behind the dam, a water body now called Lake Vesiloo named after the designer of the dam. Water level in the upper lake has remained stable for 45 years, which proves permeability of piled overburden material consisting of limestone, clayey sand and peat. For evaluating the influence of mining on a larger area, a modflowgroundwater model was set up by independent company AS Maves in cooperation with Mining Department of Tallinn University of Technology [19]. The model is supported by continuous monitoring of water wells and mine-dewatering data. For closing the existing open trench, placement of mine front and stripping technology were changed. The direction of mine front had to be changed by 45 or 90 degrees (see Fig. 5). This could enable building of an infiltration barrier between the lakes and the mine at the end of the trench where only a 30-m-wide pit would be temporarily opened for water infiltration. 36.1m 30.3m Spoil 5.8m Bank Mine bottom Infiltration dam Vesiloo lake Fig. 4. Cross-section of infiltration dam in the mined-out area of Viivikonna section. Water level in Lake Vesiloo has remained 6 m higher from water level in lower lake for 45 years 8 I. Valgma, H. Torn, K. Erg Fig. 5. Layout of water inflow to the mine applying old technology (above), new technology (below) Dragline ES-10/70 is used for piling the dam. Ordinary selective piling of the overburden will be finished at 50 m from the border. Beginning from this point, the material will be disposed homogeneously. Different materials are dumped on top of each other. This should guarantee low permeability of the dam. Important is that the material be dumped from the maximum height of dumping position of the dragline and onto different locations. The width of the dam should be at least 25 m, and the high wall should be covered with a mixture of clayey material and peat. Stripping productivity in the section will be decreased by several factors. Dragline’s cycle time increases because of hauling of the bucket to the maximum height of the dump, repositioning of the boom in every cycle, and careful monitoring of homogenisation of the spoil. Besides, technology of seam extraction in the dam area is affected by many factors. Oil shale interlayer C/D has to be hauled away from the location of the dam because of its high swelling value (up to 200%). Hydraulic conductivity The Impact of Infiltration Dam on the Groundwater Regime in the Kurtna Landscape Reserve Area 9 of this loose material could reach 1000 m/d. Alternatively, the seam has to be extracted non-selectively, leaving a 30-cm limestone layer in the output material. The overall productivity will decrease because the trench is short – 700 m, the optimum length being 1.5 km [21]. This concerns organising stripping, haulage and dam operations in a short section. Optimum length of the section was achieved by positioning the trench at 45 degrees instead of planned 90° in relation to the original North-South direction. (see Fig. 5) The groundwater model was made on several assumptions. Groundwater discharge from the mine should be within certain limits to keep the decrease in the water level of the lakes below the agreed limits. According to the model, hydraulic conductivity of the dam material should not exceed 0.1 m/d. Besides, infiltration basins which are located between the mine front and the lakes should be fed with water in an amount of 7000 m3 /d for complementing soil water of the surroundings and keeping water level in the area stable. Dam material consists of silty fine-grained sand whose modulus of hydraulic conductivity k = 0.1–0.8 m/d depending on density and compaction index of the material, and the content of clay particles. Provided that the test section was piled according to the design, the modulus of hydraulic conductivity of the material in this section could be in limits k = 0.1–0.2 m/d. In addition, the overburden contains moraine (k = 0.01–0.05 m/d), fine-grained sand (k = 0.5–2 m/d) and loose broken limestone (k = 100 m/d). Spoil material dumped conventionally is characterised by k = 0.5–50 m/d. It is assumed, basing on the experience gained from the test section, that fine material will fill spaces in coarse material decreasing permeability of the bank dam. The given solution will not work with drains that could form in the case of piling C/D layer, or with open dewatering tunnels under oil shale bed. The influence of mining on water level and quality of lake water near the test section is unnoticeable that proves the suitability of the technology. However, the conditions will become more complicated in southern direction (see Fig. 6). There are peat, sand and moraine layers in the cross section of the Quaternary sediments and Ordovician limestone in hard overburden, causing high permeability of the spoil. An increase in the thickness of limestone seam in southern direction causes most of the dumping problems in dam building. Additional amounts of sand have to be scraped from aside, probably rehandling the overburden, and, in addition, compactors should be used for achieving proper modules of hydraulic conductivity. Dam piling was modelled applying the geometric model that is used for determining the ultimate pit depth for draglines [9]. The model yields figures about suitability of draglines, need for rehandling and additional scraping, and also differences in the final height of the ground (see Figures 7 and 8). The test section has shown that it is difficult both organisationally and technologically to establish all these parameters. For evaluating the effectiveness of the dam in the southern part, several tests on density, compression and permeability of the spoil material have to be performed and compared with data obtained using the hydrogeological model. 10 12 17 22 27 32 37 42 47 Height, m Soft overburden 13.9 15.5 13.6 10.8 10.9 Hard overburden 5.1 4.2 8.0 9.9 12.1 Oil shale seam 2.8 2.8 2.8 2.8 2.8 Bottom layer 23.2 22.3 19.2 17.5 13.6 1-North 2 3 4 5- South Fig. 6. Thickness of limestone overburden increases in southern direction causing dumping difficulties for draglines and higher hydraulic conductivity of overburden material Fig. 7. Pit at the end of the trench before 1997. Limestone pile on the bottom of the trench forms under spoil drainage channels If the technology of dumped spoil fails, the compactors on the spoil and a geomembran barrier on the bank wall made using contour blasting, or a clay barrier must be applied. The Impact of Infiltration Dam on the Groundwater Regime in the Kurtna Landscape Reserve Area 11 0 10 20 30 40 -100 -80 -60 -40 -20 0 20 40 60 Dragline center Spoil Bank Length, m Fig. 8. Pit layout and modelling of surface height using geometrical model Different materials and constructions are widely used to reduce hydraulic permeability at exploitation of mines, quarries and waste depositories. Depending on purposes, the barriers, dams, sheet piles or cut-off walls of different permeability could be constructed. In Estonia, hydraulic barriers are designed and constructed around Sillamäe Radioactive Waste Depository (bentonite slurry cut-off wall) and Tallinn old municipal landfill (vinyl sheet-pile wall). Watertight clay barriers are widely used in construction of new landfills. Vertical slurry cut-off walls Slurry cut-off walls are vertical walls constructed by excavating a trench and simultaneously filling the trench with a bentonite slurry. The bentonite slurry forms a thin (typically ≤3 mm) filter cake of low hydraulic conductivity (