Characteristics of Hazardous Airborne Dust Around an Indian Surface Coal Mining Area

Transcription

1 DOI /s Characteristics of Hazardous Airborne Dust Around an Indian Surface Coal Mining Area Mrinal K. Ghose S. R. Majee Accepted: 30 June 2006 # Springer Science + Business Media B.V Abstract Surface coal mining creates more air pollution problems with respect to dust than underground mining. An investigation was conducted to evaluate the characteristics of the airborne dust created by surface coal mining in the Jharia Coalfield. Work zone air quality monitoring was conducted at six locations, and ambient air quality monitoring was conducted at five locations, for a period of 1 year. Total suspended particulate matter (TSP) concentration was found to be as high as 3,723 μg/m 3, respirable particulate matter (PM10) 780 μg/m 3, and benzene soluble matter was up to 32% in TSP in work zone air. In ambient air, the average maximum level of TSP was 837 μg/m 3, PM μg/m 3 and benzene soluble matter was up to 30%. Particle size analysis of TSP revealed that they were more respirable in nature and the median diameter was around 20 μm. Work zone air was found to have higher levels of TSP, PM10 and benzene soluble materials than ambient air. Variations in weight percentages for different size particles are discussed on the basis of mining activities. Anionic concentration in TSP was also determined. This paper concludes that more stringent air quality standards should be adopted for coal mining areas and due consideration should be given on particle size distribution of the air-borne dust while designing control equipment. M. K. Ghose (*) : S. R. Majee Centre of Mining Environment, Indian School of Mines, Dhanbad , India ghosemrinal@eudoramail.com Keywords overburden. coking coal. work zone. ambient. fugitive. respirable 1 Introduction In India, coal production will have to be increased to meet the energy demand over the next years at the rate of Mt/year. To meet the energy demand and overall coal production, opencast coal mining has grown at a phenomenal rate, and in , when the country produced 274 Mt, the opencast mines accounted for 68% of the coal production in the country (Kumar 1995). By 2000, the coal production from surface mining rose to 250 Mt, which was about 70% of the total coal production. In underground coal mining, the miners suffer from coal dust inside the workings but, in surface mining, the air pollution problem is much more acute, particularly with respect to dust pollutants. In opening an opencast mine, massive overburden (OB) has to be removed to reach the mineral deposit (Ghose 1989). This may require excavators, loaders, dumpers, and conveyor belts, which results in massive discharge of fine particulates from OB material. Similarly, normal operation will require excavation, size reduction, waste removal, transportation, loading, and stockpiling. All will release particulate matter. Closure of the mine is similar to that of opening, but for a shorter period. It is reported (Cowherd 1979) that vehicular traffic on haul roads of mechanized opencast mines could contribute as much as 80% of the dust emitted. It

2 has been estimated (Chadwick et al. 1987) that about 50% of total coal dust released is during journey time on an unpaved haul road, while 25% is released during loading and unloading of dumpers. Drilling is perhaps the next important source of fugitive dust (Nair and Sinha 1987). Finally, another major source of fugitive dust is due to wind erosion from coal stockpiles. Generally, the fines produced by surface coal mining operations contain coal particles, shale and dust particles (Addis et al. 1984). The average size of fines produced depends on different working sites. It is reported (CMRS 1961) that the specific gravity of fines produced in coal mining vary from 1.23 to 1.7 g/ cm 3, average loss on ignition was 8 10% and free carbon was 15 20%. It has also been reported that coal mining particulates are respirable in nature and hazardous to human health. The benzene soluble matter and lead concentration in total suspended particulate matter (TSP) were also found to be hazardous to human health. As the production of coal by opencast mining is growing, it is essential to evaluate its impact on the air environment and also to assess the characteristics of the emitted airborne dust, which is harmful to human health and vegetation. These data are essential for the effective design of air pollution control equipment, such as cyclone separators, scrubbers, and sprayer nozzles, which are generally used in mining, and also for setting a rational air quality standard for coal mining areas. This paper reports the fact-finding survey for the evaluation of the characteristics of the air-borne dust emitted by one of the largest opencast coal projects in the Jharia Coalfield. 1.1 Coal mining in Jharia coalfield (JCF) The Indian reserve of coking coal is mainly located in the JCF of Bharat Coking Coal Ltd (BCCL). This is situated in the Dhanbad district of Jharkand state. Coal exploration started intensively in this coalfield in 1925 (Fox 1930). Soon after the exploration period, it gained its pre-eminent position because it was the main producer of prime coking coal in India. There are 25 workable coal seams, each of 1.2-m-thick making up a total thickness of about 70 m. The bulk of the coking coal used in the steel and iron industry in the country is obtained from these seams. The Coal Council of India estimated (1963) that 13,402 Mt of coal are present in seams 0.5 m and above in thickness and to a depth of 610 m. Of this, about 5,160 Mt are classified as prime coking, 2,100 Mt are medium coking, and the rest are non coking coal. JCF is about 38 km long in the east west and 19 km wide in the north south direction. Mining in this coalfield is intensive, because of the availability of thick coal at shallow depth. This field is divided into 14 areas. The field accounts for more than 30% (27,000 t of prime coking coal per day) of the total Indian coal production. It is one of the most air-polluted coalfields due to intensive mining activities and mine fire. 2 Details of the Opencast Coal Project (OCP) Under Study The study area is one of the largest OCP for coking coal in JCF and has 34.6 Mt of quarriable reserves of coal. The project report was sanctioned in the year 1982 for a targeted production of 2.5 Mt/year, and the life of the project was 17 years. The quarry was being worked in two patches through separate box cuts. Working depth during the study period was about 60 m in box cut section and work was going on in X (No. 10) seam, having a thickness of 9.62 m. The project is located in the north-west of JCF in Dhanbad, Jharkhand, and covers an area of about 6.8 sq km. Many other opencast and underground coal mines surround it. The main drainage of the region is through the Jamuni River. The region has a tropical monsoon type climate. The general wind direction is from the west with few clouds from December to February. Air originating from the sea to the east and south brings about 80 85% of annual rainfall in June through August. The winter season extends from November to February with temperatures as low as 5 C, and the summer season is from March to June with the highest temperature experienced 48 C. The rainy season starts in late June and ends in September, with the southwest monsoon bringing the major precipitation. The annual rainfall in this region is 1,197 mm. The potential sources of air pollution in the area are Drilling and blasting Loading and unloading of coal and overburden (OB)

3 Table 1 Location of work zone monitoring stations Station no. Station site Location BW1 Feeder breaker Roof of feeder breaker control room at about 3 m above the ground BW2 Haul road (HR1) At a height of about 2 m on the debris at one side of the haul road BW3 Haul road near box cut 3 section (HR2) On the other side of haul road near the box cut 3 office at about 3 m above the ground BW4 Dragline section At a distance of 100 m from the dragline and at about 2 m above the ground BW5 Shovel/dumper loading Immediately above the working bench BW6 Workshop Roof top of a room near the workshop area which was about 3 m above the ground The movement of heavy vehicles on haul roads Dragline operations Crushing of coal in feeder breakers Wind erosion Presence of fire Exhaust of heavy earthmover machinery (HEMM). 3 Methodology Work zone air quality monitoring stations were selected near the operating sources of air pollution (Ghose and Banerjee 1995). Work zone (around the source of air pollution) air quality had been studied to assess the impact on the workers performing their duties in the work zone and also to see how much dust generated is getting dispersed into the atmosphere to increase levels of ambient air pollution. As the project is surrounded by a number of coal mines and their allied activities it is essential to know the background air pollution level in order to assess the actual contribution of pollutants by this project. In the present context, attempts had been made by monitoring of air pollution at upwind and downwind sampling locations within the coal-mining complex. Plumes are transported in downwind directions, so samplers placed immediately upwind and downwind of the project can measure pollutants emanating from OCP. The upwind sampler measures the background concentration of the pollutants of interest and the downwind sampler measures the impacts due to the dispersion of the pollutants originating within the OCP. Simultaneously, an identical sampler located at the centre of the project measures the total concentration of pollutant emanating from both the project and the background. The difference in concentration of pollutants between the central and upwind (background) measurements may be considered as the actual contribution of pollutants by the project activities in question. The difference between the central and downwind measurements may be considered as a measure firstly of the impacts of the Table 2 Locations of different ambient air monitoring stations Station no. Station site Nature of area Direction from Block II OCP Location BA1 Block II OCP Industrial Centre On the roof top of the Block II pit office about 4 m above the ground level BA2 Benidih OCP survey office Industrial E On the roof top of the survey office about 4 m above the ground and 2 km away from BA1 BA3 Nudkhurkee Residential W On the roof top of a villager s house about 7 m above the ground and 2.5 km away from BA1 BA4 Madhuband Residential SE On the roof top of a villager s house about 3 m above the ground and 2.5 km away from BA1 BA5 Benidih hospital Sensitive NW On the roof top of the hospital about 4 m above the ground and 2 km away from BA1

4 Fig. 1 Locations of the ambient air monitoring stations in the study area project activities in the surrounding locations outside the mine and secondly of the dispersion characteristics of the pollutants. The details of the work zone and ambient air monitoring stations are given in Tables 1 2, and the locations are shown in Fig. 1. Ambient air monitoring stations were selected to the west and northwest of the areas based on the prevailing winds (Ghose et al. 1999; Ghose and Sinha 1990). One ambient air monitoring station was located in the project office of OCP. During the selection of ambient air monitoring stations, the approach was to put two monitoring instruments upwind (west and northwest) and two instruments downwind (east and southeast). The approach was also to see that these monitors would sample within the industrial and residential areas, as well as sensitive areas such as the hospital, as different standards have been laid by the Central Pollution Control Board (CPCB), Government of India, for these areas (Banerjee et al. 1996). The sampling was continued twice a week for 4 weeks per month of each season covering winter (January), summer (May June), monsoon (August) and post Table 3 Work zone air quality at different sampling stations during different seasons, 24-hr average in μg/m 3 Station no. Winter season Summer season Monsoon season Post monsoon TSP PM10 TSP PM10 TSP PM10 TSP PM10 BW1 1, , BW2 2, , , BW3 1, , , BW4 3, , , , BW5 1, , , BW6 1, , Note. TSP = suspended particulate matter; PM10 = respirable particulate matter

5 monsoon (October) during the year 1996 (Ghose and Majee 2000a). Air samples were collected for 24 h in three 8-h periods ( , , hours) corresponding to daytime, evening and night time (Merefield et al. 1995). Micrometeorological data were collected on sampling days, including wind direction, wind velocity, humidity, and temperature. (Ghose and Majee 2000b, c) For the collection of TSP samples, glass fiber ambient (GF/A) filter paper was used in a high volume sampler (HVS) (Pless-Mulloli et al. 2000) manufactured by M/S Envirotech, New Delhi. The flow rate for collection of samples was maintained at m 3 /min that allows the TSP (particulate matter within the size range of 0.1μ to 100μ) to deposit on the filter paper. The mass concentration of the TSP was computed by measuring the mass of the collected particulates and the volume of the air sampled. The collected TSP was analyzed for physico-chemical characteristics, and the parameters selected for analysis were (a) particle size, (b) benzene soluble matter (tarry matter) and (c) inorganic constituents (concentration of watersoluble ions SO 4 =,NO 3,Cl ). Particle size of TSP was analyzed by Micron Photosizer, manufactured by Seisin Enterprise, Japan (Model SKN 1000), the operation based on sedimentation and the photo extinction principle. Attachment of a centrifuge to the unit made it possible to determine the size distribution down to 0.02 μm. The main principle governing the technique is the Stoke s equation, which determines the relation between size and sedimentation time of a particular sample if the specific gravity of the sample as well as medium and viscosity of the medium is known. A fine beam of light passing through a suspension is used as the measuring tool. The attenuation of light produced by the suspended particles is a function of the concentration of the particles. In the Micron Photo Sizer, homogeneously disbursed particles in a liquid medium are placed in a sample cell and a beam of light is allowed to pass through it at a fixed height from the surface of the liquid. A respirable dust sampler (RDS) manufactured by Envirotech, New Delhi, was used to determine respirable particulate matter (PM10). In the RDS, particles larger than 10 μm are removed by a cyclone, and the air containing the PM10 travels up and is collected on GF/A filter paper (Pless-Mulloi 1995). Particle size analysis was also done by Cascade Impactor (Graseby, Anderson, UK). Table 4 Ambient air quality at different sampling stations during different seasons Winter season Summer season Monsoon Post monsoon Yearly Sampling station Range Mean SD Range Mean SD Range Mean SD Range Mean SD Average TSP Concentration in μg/m 3 BA BA BA BA BA PM10 concentration in μg/m 3 BA BA BA BA BA

6 Benzene soluble matter was estimated according to IS:5182 (Part XII) (1974) For this analysis, part of the TSP deposited on the filter paper was placed in a thimble and the benzene extract was prepared using soxhlet apparatus and redistillation method. The extract was concentrated to 5 ml and the remainder of the solvent was removed by heating. The mass difference of the container with the residue and the blank gave the benzene soluble matter in the sample. The inorganic constituents of TSP were analyzed by standard methods. Water-soluble nitrate content was analyzed by xyenol method, chloride by turbidimetric method and sulphate content by glycerol-alcohol method. 4 Results and Discussion The results of the work zone air quality measurements are given in Tables 3. The highest concentration of SPM was found in the dragline section (BW4). The next lower concentration was observed at the haul road (BW2). Due to wind erosion these dusts cause more problems in opencast projects. Box cut 3 office near the haul road (BW3) showed somewhat lower TSP concentration than the haul road (BW2). It may be due to the spraying of water on the haul road near this office. The feeder breaker unit also showed higher TSP concentration. During the monsoon, the TSP concentration was found to be the lowest, but even so TSP concentration exceeded the permissible limit specified by CPCB for industrial zones (500 μg/m 3 )atnearlyall locations. The TSP concentration during daytime was found to be the highest compared to the other two time periods. This may be due to the fact that major activities were done during general shifts (i.e., from 0800 to 1700 hours). The results of the respirable particulate matter (PM10) measurements also showed a higher concentration during different seasons with the highest during the summer. The results of the ambient air quality of different samples are given in Table 4, which provides the status of air pollution during the year. These data reveal that Fig. 2 Locations of the air monitors on wind rose diagrams at different seasons

7 Table 5 Benzene soluble fraction in TSP Ambient zone Work zone Station BSF% Station BSF% BA BW BA BW BA BW BA BW BA BW Fig. 3 Average particle distribution of TSP in ambient air and work zone air TSP concentration at almost all the locations exceeded the permissible limits specified by CPCB during winter, summer and post monsoon periods. In fact, they exceeded the permissible limits specified for industrial (500 μg/m 3 ), residential (200 μg/m 3 ) and hospital (100 μg/m 3 ) areas. During the monsoon period, TSP concentration was found to be within the permissible limit due to the removal of dust particles with rainwater. PM10 concentration in the industrial location (BA1) also exceeded the permissible limit (150 μg /m 3 ). Ambient dust information showing the total distance that ambient dust disperses at different seasons is shown on the wind rose diagrams (Fig. 2). The distances between the different monitors and the total distance of dust transport are given in Table 2. TSP collected during summer (May June), monsoon (August), post monsoon (October) and winter (January) from both ambient zone and work zone air were analyzed for particle size distribution with a Seishin Micro Photosizer. The actual physical diameter can also be related to aerodynamic diameter. Results of average size distribution of TSP in work zone air and ambient air are shown in Fig. 3. Itis evident that particle size less than 10 μm was 20 26% of total SPM in work zone air and 18 23% in ambient air. Thus, work zone air is more dangerous in respect of the respirable fraction of dust. It was found that both the zones had a very small weight percentage of particle size above 60-μm size (Fig. 3). The particle size analysis of work zone TSP samples revealed that the weight percentages lying within different size ranges were a function of mining activity. The weight percentage of respirable fraction in haul road TSP was found to be higher than that of feeder breaker TSP. This may be due to continuous crushing and release of fine dust in the haul road while only one crushing was done in the feeder section. The dragline section and loading section also showed a higher fraction of respirable dust in comparison to feeder breaker and the workshop. PM10 results revealed that work zone air had a higher concentration of RPM than the ambient air. The dragline section had the highest annual average of PM10 concentration (604 μg/m 3 ). The annual average PM10 concentration was 463 μg/m 3 at the haul road, 205 μg/m 3 at the feeder breaker, 195 μg/m 3 at the shovel/dumper loading, and 298 μg/m 3 at the workshop. The concentration of PM10 exceeded the permissible limit (150 μg/m 3 ) during the winter with the average of 169 μg/m 3 at station BA1. Particle size analysis by Cascade Impactor indicated that at the ambient air station BA1 (industrial) the size range 0 2 μm had a weight percentage of 48.2% and at Table 6 Anions in ambient air TSP Station Average anion concentration (%) SO 4 = NO 3 Cl BA BA BA BA BA

8 BA4 (residential), at a distance of 2.5 km from BA1 (Table 2), it was 54.5%. This may be due to dispersion of finer particles over longer distances to residential zones. The results of particle size analysis obtained by RDS, Micron-Photosizer, and Cascade Impactor are comparable. It was observed that the median diameter of TSP was around 20 μm, which indicates that the particles are finer (Ghose and Banerjee 1997). The study also reveals that due emphasis should be given to particle size distribution when adopting air pollution control measures, and these data may be useful for the proper design of air pollution control equipment for coal mining areas. Benzene soluble matter indicates that exposure to PAH can occur. The sources of benzene soluble matter in coal mining areas are due to mine fire, burning of coal, blasting, movement of vehicles, etc. Benzene soluble matter ranged from 11 to 30% in ambient air samples and 16 to 32% in work zone air (Table 5). The maximum concentration was found at the industrial location (BA2) and at the haul road (BW2). These high values indicate the possibility of serious health hazards, as this material is carcinogenic (Ghose and Banerjee 1997). The results of anion concentration measurements in ambient air (Table 6) showed that the sulphate content varied from 1.6 to 4.4%, nitrate content from 0.06 to 2% and chloride content from 0.4 to 1.9%. Maximum concentrations were observed at the industrial location BA2. Compared to the international standard, the air quality has deteriorated to unacceptable levels. There is no epidemiological data available in India to correlate air quality with the health status of the general population. However, it can be stated that, based on available data, there could be considerable problems caused by the air pollution, especially when poverty and malnutrition are so rampant in the area. 5 Conclusion Due to opencast coal mining, the work zone as well as ambient air were found to be highly polluted with respect to dust in the study area. The respirable fraction, anion concentration, and benzene soluble matter in SPM were found to be alarmingly high and may affect human health. Dispersion of these finer particles creates serious problems in and around mining complexes. More stringent air quality standards should be adopted for coal mining areas to prevent harmful effects to human health and vegetation. These data may be useful for the effective design of air pollution control equipment for coal mining areas. Broader discussion of the problem suggests that the social and the environmental cost must outweigh the economic benefits of mining. This study should make mine officials aware of the contribution of airborne dust by opencast coal mining and their characteristics, and should enable them to take appropriate steps for environmental management. The methodology adopted can be used as a guideline on industrial scales for various sites. Acknowledgements The authors are thankful to the Ministry of Environment and Forests, Govt. of India, for supporting grants for infrastructural facilities at Centre of Mining Environment, Indian School of Mines, Dhanbad. Financial support in the form of fellowship received from University Grants Commission by the author (S.R.M.) is gratefully acknowledged. References Addis, M. C., Simons, I. G., Smart, P. L. (1984). The environmental impact of opencast operation in the forest of Dean, England. Journal of Environmental Management, 19, Banerjee, S. K., Dhar, R. K., Ghose, M. K. (1996). Air pollution due to coal washery projects and its abatement measures. Environmental Management, 20(2) Chadwick, M. J., Highton, N. H., Lindman, N. (1987). Environmental impacts of coal mining and utilization (p. 295). England: Pergamon Press. CMRS (1961). Dust problem due to washery, Central Mining Research Station, Dhanbad. Coal Council of India, Cowherd, C. Jr. (1979). Measurements of fugitive dust emissions from haul roads. Report No. EPA-600/ , Research Triangle Park. NC: USEPA, Industrial Environmental Research Laboratory. Fox, C. S. (1930). The Jharia Coalfield Memorandum. Geological Survey of India, p. 56. Ghose, M. K. (1989). Pollution due to air borne dust particles in coal mining, its monitoring and abatement measures. Minetech, 10(1), Ghose, M. K., Banerjee, S. K. (1995). Status of air pollution caused by coal washery project in India. Environmental Monitoring and Assessment, 38(19), Ghose, M. K., Banerjee, S. K. (1997). Physico-chemical characteristics of the air borne dust emitted by coal washeries. Energy Environment Monitor, 13, Ghose, M. K., Majee, S. R. (2000a). Status of air pollution in Indian opencast coal mines. Minetech, 21(2), Ghose, M. K., Majee, S. R. (2000b). Assessment of dust generation due to opencast coal mining- an Indian case study. Environmental Monitoring and Assessment, 6(2), Ghose, M. K., Majee, S. R. (2000c). Assessment of impact on air environment due to opencast coal mining- an

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