Lind robam valgma_sokman_developing_computational_groundwater_monitoring_and_managment_system_for_estonian_oil_shale_deposit_geoenv08
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Lind robam valgma_sokman_developing_computational_groundwater_monitoring_and_managment_system_for_estonian_oil_shale_deposit_geoenv08 Document Transcript

  • 1. 2nd International Workshop in “Geoenvironment and 1 Geotechnics”, September 2008, Milos island, Greece Developing computational groundwater monitoring and management sys- tem for Estonian oil shale deposit H. Lind, K. Robam and I. Valgma Tallinn University of Technology K. Sokman Estonian Oil Shale Company ABSTRACT tive and prospective mining areas. The goal for the model is to generate descriptive three and Mining in Estonian oil shale deposit mainly two dimensional dynamic water table maps de- takes place in the Ordovician, Keila-Kukruse picting hydrogeological conditions, in order to aquifer. The aquifer is affected by mining and is provide information regarding the changes of fully dried out around the working mine areas the water dynamics (i.e. from the graphical (Perens and Savitski, 2008). The groundwater maps of water flow directions), as well as dia- level is decreased down to 30 m, to the mine grams and reports of water in- and outflow. floor elevation using about 30 pumping stations Also information about the water exchange be- (Lind, 2005). The pumping rate is very high - tween mines is considered useful (Reinsalu and depending on the season, ranging from 10 up to Valgma, 2003; Reinsalu, 2005), as well as the 40 m3 per ton of produced oil shale (Reinsalu water income rate into working mines. Today et al., 2006). The Estonian oil Shale Company the monitoring system used by Oil Shale Com- mined 15.5 million tons of oil shale in 2007 pany is not very flexible to analyze the situation (Source: Estonian Oil Shale Company). In order and to create a dynamic model; a MS Excel to predict the effects, and avoid the social and worksheet with diagrams and a static model of environmental impacts, there is a need to con- groundwater level was created previously. The tinuously monitor the situation and run software research project presented here will create a sys- simulations aiming at decreasing the pumping tematic database for developing a computational rate. This becomes even more important since groundwater model of the oil shale deposit for the environmental taxes on usage of groundwa- sustainable management. ter resources increase every year. Therefore, it is necessary to monitor groundwater level and quality, and develop a groundwater model for 2. INPUT DATA FOR MODELING the overview of the situation during mine opera- In order to build up the groundwater model it is tions and also for a number of years after mine necessary to have a lot of detailed input data in closure. a structured form. For a simplified model at least information about the geological layers, 1. INTRODUCTION the hydraulic conductivity, observation wells, pumping wells and boundary conditions is The aim of the research is to develop and reor- needed. For importing the data into the Visual ganize monitored groundwater data by Estonian ModFlow software some data processing is re- Oil Shale Company and build a dynamic quired. For the monitored water level data until groundwater model in order to create a sustain- today simple MS Excel worksheets were used. able groundwater monitoring and management Currently collected data did not allow analysis system. The monitored data is used as input data of the information and easy extraction of the for the hydrogeological modeling using the Vis- needed output for groundwater modeling. ual ModFlow Professional software for the ac- A MS Access database was created in order
  • 2. 2 2nd International Workshop in “Geoenvironment and Geotechnics”, September 2008, Milos island, Greece to record continuously monitored observation well data in a structured form. Also MapInfo and its addition Vertical Mapper are used to generate background information. For inserting already existing data, a comfortable layout was developed to copy the information from MS Ex- cel worksheet into MS Access database. New observed records for a certain observation well will be added using a form, as there is no need to insert well number, information of aquifer Figure 2: Groundwater model of Oil Shale deposit created with Visual ModFlow. and geography. Each observation well in the da- tabase has a unique identification number to use as a link in different query tables. Query tables are used to extract only the needed information 3. BUILDING A GENERAL GROUNDWA- from the main table; in addition, the monitored TER MODEL information at certain time is added using que- Mathematical models have a key role in assess- ries as filling the main database table with ob- ing the future behavior of a system to find effec- served information at different time periods tive operating conditions for sustainable devel- would be too complicated. Using query tables opment and management groundwater re- the information needed for groundwater model- sources. Besides the importance of organizing ing with Visual ModFlow software can be easily mining operations, advanced groundwater moni- exported. Output can be given selectively by toring and modeling techniques are useful for monitored time, by aquifer and by geographical environmental impact assessments, while differ- well location. The database will be further de- ent infrastructure objects are planned to be build veloped to give seasonal average water level per nearby closed and waterfilled underground observation well as the groundwater level varies mines. seasonally. The groundwater model of an oil shale de- The MS Access database together with posit is under development using the Visual linked geographic data by MapInfo Professional ModFlow software. The developed model will software (Fig. 1) allows visualizing the well lo- be dynamic; the data obtained through monitor- cation on a two dimensional map. All informa- ing can be used to rerun the model and obtain tion added to the main table of the described da- results in real-time. As the software takes into tabase can be presented. MapInfo is used to account different parameters, including geologi- generate simple static groundwater level mod- cal, hydrological and hydrogeological data, it is els, where the average water table elevations are necessary to restructure current databases and generated from linked database as the Visual collect the additional input data necessary for Modlow is rather inflexible to create simple the model. One of the difficulties when creating static models. In addition, the user can not eas- the model is to collect and process the informa- ily change interpolated data that Visual Mod- tion needed for building and running the model. flow generates based on measured data. The area of the model is 127 x 55 ≈7000 km2 which includes mined out and prospective areas of oil shale (Fig. 2). As the model area is large, the accuracy of the results will be low and, hence, the output will be used for a general overview of groundwater dynamics. The created model has a grid size 100x100 m and has five main layers - on top is the ground, below it a 1 m thick soil layer, then limestone and an oil shale layer. The bottom of the model is a water impermeable layer (mainly the Uhaku Figure 1: Map of oil shale deposit with observation well geological bed) (Fig. 3). For the grid layer in- database linked with Access database. formation, previous research information cre-
  • 3. 2nd International Workshop in “Geoenvironment and 3 Geotechnics”, September 2008, Milos island, Greece Figure 3: Visualisation of the model layers – ground layer and layer of oil shale. Figure 5: Part of mined out and prospective area (Aidu opencast), observation wells can be seen. ated with MapInfo Professional was utilized. Today line information available in the model includes rivers and streams, investigation areas and mined out areas (properties and 4. WATER QUALITY MANAGEMENT boundary conditions for these areas can be When the mine will be closed down, the added later) (Fig. 4). groundwater level will increase within two to Also, observation wells have been added as four years up to the level as it was before the calibration data for the model (Fig. 5). While economic activities started (Reinsalu et al., adding the wells the following problem was en- 2006). Changing the groundwater regime during countered: the interpolated model domain was and after mining will result in an increase in cer- smaller than the actual observation well depth. tain chemical components of the groundwater. Therefore not all wells are entered since the The 2004 data showed a higher rate of sulphate software is rather inflexible to enlarge the model content, total Fe, total oil products and total boundaries. phenol in the water sampled from the closed - As the area of oil shale deposit is more than waterfilled - underground mine, which exceeded 2700 km2 the model can include only the basics the drinking water norm (Reinsalu et al., 2006; for the general overview; when a detailed inves- Erg, 2005). tigation is needed for a certain location a Therefore it is also necessary to monitor the smaller model can be developed (extracted) water quality in the closed mine and of the from the larger model. As there is lack of data pumped water from the mine which is settled in for the area surrounding the oil shale deposit it settling basin before directing into nearby rivers may be necessary to create inactive areas around or dikes. It is also necessary to monitor seasonal the deposit. changes in the concentrations of chemicals in the mine water. Hence, the groundwater quality management program has been started in differ- ent parts of the oil shale deposit. The model of water dynamics will be developed further for managing groundwater quality. 5. FURTHER DEVELOPMENT Developing the management system the ob- served data should be gathered in a structured form to insert the specified input data into the groundwater model. To create a simplified model the following data should be collected: Figure 4: Inserted line information - rivers, lakes, pro- geological layers, hydraulic conductivity, ob- spective and mined out areas. Coloured background de- servation wells, pumping wells and boundary scribes ground elevation. conditions. Further development of the model
  • 4. 4 2nd International Workshop in “Geoenvironment and Geotechnics”, September 2008, Milos island, Greece foresees the creation of a database of pumping Computational mathematical models can be wells to be inserted into the model. Pumping used to allocate the technical and environmental wells will show the influence and changes on constraints. the water level nearby the mine workings. Also To conclude it should be mentioned that the the model will give information to optimize software package will be used to have a compu- used pumping capacities and also reorganize the tational groundwater model to simulate condi- location(s) of the pumping stations where it is tions at technogenic mining areas. Today is im- technically possible. portant to predict the influence to the environ- More detail information will be gathered re- ment before the mine starts working. The com- garding the hydraulic conductivity at certain putational groundwater management system can layers and areas and the parameters for some of be used while new mines are opened, current the boundary conditions of the model like river, mining is progressed or to overview the situa- lake, amount of precipitation and aquifer tion at closed down mines especially if nearby groups. After specifying the input data the situa- building activity is needed. The output files tion of model should be calibrated which re- from the software can be used to visualize the quires the equal values of observed and calcu- current and also the future conditions after geo- lated water table values. This requires running logical changes by mining development. The the software and analyzing the results several output data can be used for economical calcula- times before receiving any results. While the tions as well. created model is very large and while it goes The current project is done as part of the re- more and more detailed there can be limits on search “Conditions of sustainable mining” capacity of regular computer. ETF7499, whose scope is to use computer mod- eling to form the basics for sustainable, envi- ronmentally friendly mining. 6. CONCLUSIONS A groundwater management system in Estonian REFERENCES oil shale deposit is necessary to be developed further in order to understand the groundwater Reinsalu, E. and I. Valgma, 2003. Geotechnical Processes dynamics and the changes in the concentrations in Closed Oil Shale Mines, Oil Shale, Tallinn: Esto- nian Academy Publishers, 398 - 403. of potential pollutants (either primary or as a re- Reinsalu, E., 2005. Changes in Mine Dewatering After sult of chemical reactions between water and the Closure of Exhausted Oil Shale Mines, Oil Shale, minerals, i.e. pyrite) in order to decrease and/or Tallinn: Estonian Academy Publishers, 261 - 273. avoid any negative impacts. Groundwater usage Erg, K., 2005. Changes in groundwater sulphate content is sustainable today, but it can become even in Estonian oil shale mining area. Oil Shale, 22 (3), more efficient by a) decreasing the influence of 275-289. Lind, H., 2005. The modelling of hydrogeological condi- mining to people living nearby active mine ar- tions. The case study of dewatering Tammiku Kose eas whose drinking water wells could be dry or surface mine, Thesis, Estonian National Library. polluted and b) avoiding any negative impacts Reinsalu, E., I. Valgma, H. Lind and K. Sokman, 2006. on environmentally protected areas. As the de- Technogenic water in closed oil shale mines, Tallinn: pression cone due to mining is very wide, influ- Oil Shale, Estonian Academy Publishers Vol. 23. Perens, R. and L. Savitski, 2008. Põlevkivi kaevandamise encing different environmentally protected ar- mõju põhjaveele (in English: Oil Shale mining influ- eas, draining wells for drinking water etc, tech- ence on groundwater). Keskkonnatehnika, 3/08, 44- nological solutions like impearmable walls, in- 47. filtration dams, pumping water from mine back to the area should be applied to keep the water level. ModFlow helps to model this situation and thus make the right decisions regarding the application of these technological solutions. Furthermore, it should be noted that if there is a need to reach drinking water quality the technical solutions are available, while the cost and economical question should be considered.