Hydro-geological and Envirollmerital Impact of coal mining in Selected Districts of Salt Range Punjab Pakistan

Abstract

Pakistan is blessed with huge coal reserves of about 185 billion tons, this black diamond has the potential to uplift the country's economic development. However, the dark side of coal, i.e., its detrimental environmental impacts always put a question mark on its consumption. Coal upon exploration via surface or sub-surface mining alters the landscape, causes subsidence, produces huge waste piles, that could raise the water table, and results in water inrush and flooding of mines. The present research has been designed in this scenario to depict the geochemical inventory of coal, coal waste, soil, and particulate matter to understand the occurrence, enrichment, distribution patterns, and mobilization mechanism of environmentally sensitive priority pollutants (including As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn). In addition, delineating the contamination status, its associated risk, and potential of coal mine damages on the water composition of aquifers was also addressed. For this purpose, extensive sampling was done from the eastern, central, and Trans-Indus range of the Salt Range Punjab, Pakistan and 59 coals samples from 15 mines, 57 soil, 131 groundwater samples, 10 mine tailings (n=10), and 8 air settleable particulate matter samples were collected and used to develop the geochemical inventory of environmentally sensitive toxicants. In addition, characterization of coal general parameters and stable isotopic (OI3C, 015N) analyses were used to rank and decipher the coal depositional environment and organic matter source. Various statistical tools such as pollution indices, principal componentmultiple linear regression analysis (PCA-MLR), and hierarchical cluster analysis (HCA) were applied to assess the possible risks, enrichment, source, and mobilization mechanisms. Groundwater samples were evaluated for hydro-geochemical evolution, water suitability for drinking and irrigation purposes. The Paleocene coals of the Salt Range in the Punjab province of Pakistan have great economic potential, but their trace element and stable isotopic archives have not been studied in detail except for a few sporadic samples. To depict the holistic picture of the coal depositional environment as well as their metallic enrichment.59 coal samples from 14 mmes have been investigated for general coal ranking, distribution, major/trace elements geochemistry, and &13C..o 15N isotopic signatures. Based on the proximate data, the studied coal samples are classified as lignite and sub-bituminous to the bituminous rank. Average contents of trace elements such as Co, Cr, Cu, Pb, Sr, Th, U, V, and Zn are 7.4, 41.7, 11.2, 12.5,90.2,4.0, 1.9, 128, and 31.1 mglkg), respectively. These values, when compared with the World Coal Clarke values, were relatively higher in lignite coals, suggesting their continuous utilization may increase concentrations of these elements in the environment. Likewise, As (20.4), Co (6.6), Cr (22.4), Cu (13.3) Pb (19.2), Sr (154.7), Th (2.5), V (47.8), and Zn (75.1 mglkg) were significantly higher in the sub-bituminous to bituminous coals of the Salt Range. Mineralogical analysis, based on X-Ray diffraction and energy dispersive X-Ray spectroscopy, revealed that the studied samples comprised illite, hematite, calcite, siderite, gypsum, pyrite, quartz, muscovite, and other clay minerals. Elemental affinity with organic and inorganic phases of coals calculated by an indirect statistical approach indicated a positive association of ash content with Ag, AI, Co, Cr, Cs, Cu, Mn, P, Rb, Pb, Th, U, and V, suggesting the presence of inorganic components in studied coals. However, As, Fe, Sr, and Zn exhibit negative correlations that imply their association with the organic fraction. The l3C and 15N isotopic range and average values for 12 coal samples were -24.94 %0 to -25.86 %0 (-25.41 %0) and -2.77 %0 to 3.22 %0 (0.96 %0), respectively, reflecting 3C type modem terrestrial vegetation as a source of peatification. In addition, the trivial variations of 0.92 %0 and 0.45 %0 among \3C and 15N values can be attributed to water level fluctuations and plant assemblies. The clusters of coal mines and waste piles considerably increase metal(loid)s concentrations in the surrounding soils and air of eastern (ESR), central (CSR), and TransIndus Salt Range (TSR). To understand the occurrence and dispersal of toxic metals from waste piles to different environmental components and their pollution load in soils and possible risk geochemical characterization of the soil, coal waste, and dust particulate matters were done. The results revealed that waste samples are highly enriched of As, Cd, Pb, Fe, and Zn with 16, 0.2, 11,51510, and 86 mg/Kg for CSR and 11,0.3, 10,37417, and 144 mglKg for TSR site, respectively. However, ESR waste samples with elemental concentrations of As (10), Pb (5), Fe (15833), and Zn (10 mg/Kg) lied within the range of the threshold limit. While soil profiles indicated that Cd, Cu, Fe, and Zn concentrations of all the sites, As of the CSR and TSR, and Pb in ESR and TSR soils were beyond the soil's background values. Based on the enrichment factor (EF), contamination factor (CF), geoaccumulation index (Igeo), and soil quality standards Fe, Cu, Cr, and Pb, and Zn were the most serious soil pollutants mainly sourced from coal associated waste piles. Further, the principal component analysis and multiple linear regression (PCA-MLR), and agglomerative hierarchical clustering (AHC) signifies that mineralization and weathering of sulfide and carbonate minerals within the coal wastes and lithological units of the present study area cause the release of environmentally sensitive trace elements, which upon volatilization, leaching, and atmospheric deposition enters the air and soils of the present study area. Such metal poisoning due to alarmingly higher As, Cd, Cu, Fe, Pb, and Zn values is a significant human health concern. Impacts of coal mining activities on groundwater quality and to understand groundwater evolution and its possible domestic and irrigation impacts groundwater samples from mining areas were collected and analyzed. Results showed that groundwater samples were alkaline with a pH range of 7.0-8.6 and 7.8-8.8 for the eastern Salt Range (ESR) and Trans-Indus Salt Range (TSR), while that of central Salt Range (CSR) was acidic to moderately alkaline ranging between 5.7 to 7.5. The water types ofCa-Mg-HC03, Ca-Mg-Cl, and Ca-Ch were the dominant hydro-chemical facies in ESR and CSR sites however, groundwater samples of the TSR site fall under Ca-Ch type water. Our new findings suggest that groundwater chemistry is mainly controlled by rock dominance and reverse ion exchange reaction, followed by evapotranspiration processes. The wells ofCSR and TSR were reported with higher levels of Fe and Zn suggesting contamination from the coal sources. Regarding the suitability for irrigation, water wells observed for sodium adsorption ratio (SAR), magnesium adsorption ratio (MAR), sodium percentage (Na%), Kelley's ratio (KR), and potential salinity (PS) suggested that all three sites (ESR, TSR, and CSR) had the potential to rise prolonged salinity hazard. The conceptual model of geochemical evolution revealed that both local and regional salinization is mainly driven by local geology and intensive coal mining activities. Besides, the neutralization capacity of parent geological formations buffers the acidity and lowers the overall trace elemental enrichment. In addition, 41 %, 57%, and 36% of the ESR, CSR, and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 50 mglL N03- Likewise, 3%, 17%, and 27% of the ESR, CSR, and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 1.5 mglL P-. These elevated values with Pollution Index (PI) and Health Risk Index (RRI) > 1 reflect a non-acceptable carcinogenic risk for drinking water N03 -and F- which should be addressed on a priority basis to protect human health. A non-acceptable carcinogenic risk associated with drinking water N03 - and F- in the Salt Range, Punjab may exist. Hence proposed extension in the mining industry in the Study area needs to be established considering the sustainable manners. Owning to the importance of economical tensions and environmental considerations, the concept of green mining and sustainable development is the need of the hour.