Groundwater and solute transport modeling in the proximity of Arad Thermal Power Plant, Romania

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1 Groundwater and solute transport modeling in the proximity of Arad Thermal Power Plant, Romania BEILICCI ERIKA BEATA MARIA, BEILICCI ROBERT FLORIN Hydrotechnics Department, Civil Engineering Faculty Politehnica University of Timisoara Timisoara, George Enescu 1A, ROMANIA Abstract: - The Paper present unconfined groundwater flow and solute transport modeling under ash storage pit CET Arad using the PMWIN applications. Modeling purpose is to constitute extending pollution zone of aquifers in space and time generated of polluted infiltration in ash storage pit CET Arad, Arad country. Knowledge of extending of pollution zone is necessary to settle technical measures to closing nonconformity ash storage pit. The companion software Processing Modflow for Windows (PMWIN) offer a totally integrated simulation system for modeling groundwater flow and transport processes with MODFLOW-88, MODFLOW- 96, PMPATH, MT3D, MT3DMS, MOC3D, PEST and UCODE. Key-Words: - groundwater, flow, solute transport, ash storage pit, pollution 1 Introduction There are a significant numbers of thermal power plants around the world and new plants are put into operation almost weekly. This rapid industrialization has resulted in an increased use of natural resources such as coal in case of fossil fuel burning power plants. All these power plants brought along serious environmental imbalance due to the dumping of industrial wastes. The main impact factors over the environment of the thermal power plants that operate on fossil fuels are as follows: air emissions, greenhouse gas emissions and use of natural resources, water supply and wastewater, storage of solid waste, noise, location. The environmental impacts should be understood also from the local population point of view. Pollutants emissions in air, soil and water have serious consequences over human health. Depending on the location of the coal mine that supplies the power plant the lignite may have different properties such as heating value, moisture and mineral content resulting in different residue upon combustion. The properties of the resulted ash are a function of several factors. Beside the coal source there are other important factors that influence its properties as follows: boiler unit, loading and firing conditions, storage and handling methods. Variations may occur from ash properties point of view not only between different power plants but within a single power plant too. The wastes generated by the power plants are the ones typical for a combustion process. Burning lignite results in exhaust gases that contain primarily particles, sulfur and nitrogen oxides and volatile organic compounds. The ash residues resulted after lignite burning may contain significant levels of heavy metals and may cause serious air, surface water and groundwater pollution. The pollutant movement through all these modes may be schematically represented like in the below figure 1: Fig. 1. Pollutant movement schematically representation. Air pollution is caused by direct emissions of gases as well as wind-blown ash from the storage pit as shown in the figure 1 and 2. The air-born fine dust can fall in surface water system or soil and may easily contaminate the water and soil systems. A ISBN:

power plant may choose one of the two ash disposal methods using either dry or wet disposal scheme.

In case of the power plants that are using the wet scheme the ash is discharged directly into the nearby surface water system.

In order to avoid heavy environmental pollution in case of a wet ash disposal scheme engineering measures have to be taken when constructing the ash pond and nevertheless a strong monitoring system

2 power plant may choose one of the two ash disposal methods using either dry or wet disposal scheme. In the case of dry disposal scheme the ash is stored in an embankment and in case of the wet disposal scheme in a so called ash pond. In case of the power plants that are using the wet scheme the ash is discharged directly into the nearby surface water system. The long storage of ash under wet conditions can cause leaching of heavy metals into the underlying soil and groundwater system. In order to avoid heavy environmental pollution in case of a wet ash disposal scheme engineering measures have to be taken when constructing the ash pond and nevertheless a strong monitoring system has to be implemented also. plants. Compliance with these local standards and regulations, where they exist, is required. Whatever the goods or services exported, all of these factors are analyzed. In case the goods or services in question only play a minor role with respect to the overall project, this situation is nonetheless taken into account in the conclusions. Environmental impacts should be understood in a broad meaning, and include, where appropriate, impact on local population. 2 Problem Formulation The Arad Thermal Power Plant is located in the northern part of Arad locality and was designed to run on solid fossil fuel (lignite) having as firing supports the natural gases (Figure 4). The plant provides the heat carrier and over 50% of the electricity for Arad city. The plant uses around tons of lignite per year. Fig. 2. Classification of fuels and technologies. The main impact factors of new thermal power plant projects that operate on combustible fossil fuels are as follows: air emissions (excluding CO2); use of natural resources and greenhouse gas emissions; water supply and wastewater; noise generated by facility operations; storage and treatment of solid waste; location; The figure 3 below presents the main pollutants concerned, the emissions factors identified as well as those measures currently available to reduce these emissions. Fig. 3. Air emissions (under normal operating conditions and excluding CO2). Most countries have adopted regulations which aim to limit atmospheric emissions from thermal power Fig. 4. Pollutant movement schematically representation. The ash storage pit is located at 1.5km away from the Arad Thermal Power Plant and extends over a surface of 65ha. It is composed of 3 compartments outlined by barriers. Currently the level in each compartment is as follows: full up to 114m for compartment no.1, full up to 114m for compartment no.2 and full up to 113m for compartment no.3. Because all three compartments are full at the moment each of them will have to be elevated to allow further storage for another 4-5 years. In each year in the storage pit are stored between and tons of ash. The surroundings of the ash storage pit are as follows: - to the north and south: agriculture fields ISBN:

- to the east: a waste management company with its waste disposal. - to the west: pasture The closest residential area is located at 3km southwest of the storage pit (Figure 5).

3 - to the east: a waste management company with its waste disposal. - to the west: pasture The closest residential area is located at 3km southwest of the storage pit (Figure 5). The ash storage pit lies on a relatively plane surface consisting of clays, sands, gravel and dust. The surface layer on which the storage pit is built is formed out of plant (vegetable) layer, dusty clays and clay sands. The drillings that were executed showed that there is an impermeable layer of 1.2m to 4.6m thick that acts as an impermeable bed for the ash storage pit. The lower layers contain sands and gravels with a high permeability followed by layers less permeable. Because the clay permeability value that was determined in the laboratory is 10-6 cm/s it was considered at the time of construction that it has been assured a proper impermeable bed for the ash storage pit. Fig. 5. Arad Thermal Power Plant and the Ash Storage Pit as seen from satellite. In the year interception and 9 control drillings were put into execution around the ash storage pit with depths varying between and m. The interception drillings are situated to the west of the storage pit and were made in order to certify the phreatic water quality. In case of pollution the purpose of these drillings is to capture the water and introduce it in the technological circuit. The control drillings are situated to the north, east and south of the storage pit and were put into execution in order to verify if there are possible polluted water leakages towards east where the tapping of groundwater for Arad city drinking water is performed. 3 Problem Solution The applications of MODFLOW, a modular threedimensional finite-difference groundwater model of the U. S. Geological Survey, to the description and prediction of the behavior of groundwater systems have increased significantly over the last few years. Models or programs can be stand-alone codes or can be integrated with MODFLOW [1]. A standalone model or program communicates with MODFLOW through data files. The advective transport model PMPATH (Chiang and Kinzelbach, 1994, 1998), the solute transport model MT3D (Zheng, 1990), MT3DMS (Zheng and Wang, 1998) and the parameter estimation programs PEST (Doherty et al., 1994) and UCODE (Poeter and Hill, 1998) use this approach [2][5][3]. The solute transport model MOC3D (Konikow et al., 1996) and the inverse model MODFLOWP (Hill, 1992) are integrated with MODFLOW. Both codes use MODFLOW as a function for calculating flow fields [6]. The companion software Processing Modflow for Windows (PMWIN) offer a totally integrated simulation system for modeling groundwater flow and transport processes with MODFLOW-88, MODFLOW-96, PMPATH, MT3D, MT3DMS, MOC3D, PEST and UCODE [4]. PMWIN comes with a professional graphical userinterface, the supported models and programs and several other useful modeling tools. The graphical user-interface allows you to create and simulate models with ease and fun. It can import DXF- and raster graphics and handle models with up to 1,000 stress periods, 80 layers and 250,000 cells in each model layer. The modeling tools include a Presentation tool, a Result Extractor, a Field Interpolator, a Field Generator, a Water Budget Calculator and a Graph Viewer. The Result Extractor allows the user to extract simulation results from any period to a spread sheet. You can then view the results or save them in ASCII or SURFER-compatible data files. Simulation results include hydraulic heads, draw downs, cell-by-cell flow terms, compaction, subsidence, Darcy velocities, concentrations and mass terms. The Field Interpolator takes measurement data and interpolates the data to each model cell. The model grid can be irregularly spaced. The Water Budget Calculator not only calculates the budget of userspecified zones but also the exchange of flows between such zones. This facility is very useful in many practical cases. It allows the user to determine the flow through a particular boundary. The Field Generator generates fields with heterogeneously distributed transmissivity or hydraulic conductivity ISBN:

4 values. It allows the user to statistically simulate effects and influences of unknown small-scale heterogeneities. The Field Generator is based on Mejía's (1974) algorithm. The Graph Viewer displays temporal development curves of simulation results including hydraulic heads, draw downs, subsidence, compaction and concentrations. Using the Presentation tool, you can create labeled contour maps of input data and simulation results. You can fill colors to model cells containing different values and report-quality graphics may be saved to a wide variety of file formats, including SURFER, DXF, HPGL and BMP (Windows Bitmap). The Presention tool can even create and display two dimensional animation sequences using the simulation results (calculated heads, draw downs or concentration). At present, PMWIN supports seven additional packages, which are integrated with the original MODFLOW. They are Time-Variant Specified- Head (CHD1), Direct Solution (DE45), Density (DEN1), Horizontal-Flow Barrier (HFB1), Interbed- Storage (IBS1), Reservoir (RES1) and Stream flow- Routing (STR1). The Time-Variant Specified-Head package (Leake et al., 1991) was developed to allow constant-head cells to take on different values for each time step. The Direct Solution package (Harbaugh, 1995) provides a direct solver using Gaussian elimination with an alternating diagonal equation numbering scheme. The Density package (Schaars and van Gerven, 1997) was designed to simulate the effect of density differences on the groundwater flow system. The Horizontal-Flow Barrier package (Hsieh and Freckleton, 1992) simulates thin, vertical low-permeability geologic features (such as cut-off walls) that impede the horizontal flow of ground water. The Interbed- Storage package (Leake and Prudic, 1991) simulates storage changes from both elastic and inelastic compaction in compressible fine-grained beds due to removal of groundwater. The Reservoir package (Fenske et al., 1996) simulates leakage between a reservoir and an underlying ground-water system as the reservoir area expands and contracts in response to changes in reservoir stage. The Stream flow- Routing package (Prudic, 1988) was designed to account for the amount of flow in streams and to simulate the interaction between surface streams and groundwater [2]. The piezometric level in the ash storage pit area was intercepted at depths between 1.2 and 5.2m. The average filtration coefficients determined by pumping are situated between 36.8 and 132m/day and in the majority of cases being higher as 81m/day. The hydrostatic level was determined concomitant in all drillings that were put into execution between years 1982 and 1983 and was recorded around 104m. It has been determined that the general underground aquifer flux running direction is in general towards SE-NW (with hydraulic slopes between and ). According to the filtration coefficients and hydraulic slopes it has been determined that the real underground running speed has values between 21 and 68m/year. The average annual temperature is recorded between 10.80C (plain) and 60C (highest locations) with maximum deflection from year to year of 20C. The maximum absolute temperature was of 41.50C (in year 1946) and a minimum absolute temperature of - 300C (in year 1954). The precipitations annual average values are around 577mm at Arad meteorological station. Average wind speed is around 3m/s. In the area of the ash storage pit the predominant wind direction is towards NW and very seldom (only 8-10 days/year) towards Livada locality situated to the east of the storage pit. Although the average speed of the wind is low there are also windy periods of time when the ash is transported by the wind towards the above mentioned locality. The aquifer is simulated using a grid of one layer, 100 columns and 100 rows. A regular grid spacing of dx = 50 m is used for each row and dy = 310 is used for each column. The layer type is confined for deep aquifer and unconfined for Shallow groundwater. The river are modeled as variable - head boundaries with hydraulic heads of h = 100 m and 120 m. All other boundaries are no-flow boundaries. Front of groundwater abstraction for water supply Arad city was modeled as wells with flow requirements. In the block-centered finite difference method, an aquifer system is replaced by a discretized domain consisting of an array of nodes and associated finite difference blocks (cells). The nodal grid forms the framework of the numerical model. Hydrostratigraphic units can be represented by one or more model layers. The thicknesses of each model cell and the width of each column and row can be specified. The locations of cells are described in terms of columns, rows, and layers. MODFLOW requires initial hydraulic heads at the beginning of a flow simulation. Initial hydraulic heads at fixed-head cells will be kept constant during the flow simulation. An IBOUND array is required by the flow model MODFLOW. The IBOUND array contains a code for each model cell. A positive value in the IBOUND array defines an active cell (the hydraulic head is computed), a ISBN:

negative value defines a fixed-head cell (the hydraulic head is kept fixed at a given value) and the value 0 defines an inactive cell (no flow takes place within the cell).

Fig. 9. Concentration in observation well in Shallow groundwater. Fig. 6. Head contour in deep aquifer and distribution of the pollutant. Fig. 7.

4 Conclusion The results of simulation permit exactly quantify evolution of concentrations in time, for all points of polluted zones.

A special remark that is not necessary to specify pollutant nature, because the modeling was making in general for all kind of pollutants.

5 negative value defines a fixed-head cell (the hydraulic head is kept fixed at a given value) and the value 0 defines an inactive cell (no flow takes place within the cell). Figure 6, 7, 8 and 9 shows the head contours, distribution of the pollutants, concentration for deep aquifer respectively for shallow groundwater. Fig. 8. Concentration in observation well in deep aquifer. Fig. 9. Concentration in observation well in Shallow groundwater. Fig. 6. Head contour in deep aquifer and distribution of the pollutant. Fig. 7. Head contour in Shallow groundwater and distribution of the pollutant. 4 Conclusion The results of simulation permit exactly quantify evolution of concentrations in time, for all points of polluted zones. This think is important to find a technical method for limitation, reduce or eliminate in time pollution. A special remark that is not necessary to specify pollutant nature, because the modeling was making in general for all kind of pollutants. The concentration values are expressed in percentage from the total quantity of pollutant. Concentration is a general parameter and maybe serve base for calculation an absolute concentration (for example mg/l) for all dissolved pollutants in water. From the concentrations diagrams the Local Authorities has possibility to know the directions and evolution in time of the pollution from landfills. The ash residues resulted after lignite burning may contain significant levels of heavy metals and may cause serious air, surface water and groundwater pollution. The ash storage pit of Arad Thermal Power Plant extends over a surface of 65 ha and therefore its impact over the environment is heavy. The water samples drawn from the control drillings indicate ph, chlorides and sulphates values that exceed the accepted limits. The transport water and phreatic water both show high values for chlorides, sulphates and hardness. The control drillings situated to the north, east and south of the storage pit were put into execution in ISBN:

6 order to verify if there are possible polluted water leakages towards east where the tapping of groundwater for Arad city drinking water is performed. References: [1] Wen-Hsing Chiang and Wolfgang Kinzelbach, 1998, 3D-Groundwater Modeling with PMWIN, Spinger-Verlag [2] Andersen P. F., A manual of instructional problems for the U.S.G.S. MODFLOW model. Center for Subsurface Modeling Support. [3] Chiang, W. H. and W. Kinzelbach Processing Modflow (PM), Pre- and postprocessors for the simulation of flow and contaminant transport in groundwater system with MODFLOW, MODPATH and MT3D. [4] Chiang, W.-H. and W. Kinzelbach, 1994, PMPATH for Windows. User's manual. Scientific Software Group. Washington, DC. [5] Chiang, W.-H. and W. Kinzelbach, 1998, PMPATH 98. An advective transport model for Processing Modflow and Modflow. Harbaugh, A. W. and M. G. McDonald [6] Hill, M. C., MODFLOW/P - A computer program for estimating parameters of a transient, three-dimensional, groundwater flow model using nonlinear regression, U.S. Geological Survey, ISBN:

SOLUTE POLLUTANTS TRANSPORT MODELING IN LANDFILL VALEA MANASTIRII, GORJ COUNTY ROMANIA

SOLUTE POLLUTANTS TRANSPORT MODELING IN LANDFILL VALEA MANASTIRII, GORJ COUNTY ROMANIA 3 Robert BEILICCI, Erika BEILICCI Politehnica University of Timisoara, Department of Hydrotechnical Engineering George