Impact of Open Pit Coal Mining on Groundwater in and Around Phulbari Area, Bangladesh

Abstract

This study attempts to evaluate current state of the groundwater environment considering natural and artificial system together, to better understand origin of stresses, their state, expected impact and responses made to restore healthy groundwater environment in Phulbari coal mine area. Impacts on groundwater were carried out for an open pit coal mining area located in Phulbari under Dinajpur District in Bangladesh. The exploration of coal following the open pit method will influence the ground water resources in and around the mine due to pumping of groundwater as well as precipitated water which will be accumulated in the floor of the open pit mine. Groundwater is the main source for agriculture and domestic use of that region. In this area the average groundwater level is declining 0.166m each year. During the drought season groundwater depletion rate is 0.209 m/year and during monsoon period this rate is 0.112 m/year. During the twenty-five years period (1985- 2010) total depletion of groundwater is 4.15 min Phulbari. On the other hand, during the summer season temperature ranges from 22°c to 38°C and during the winter season it varies from 5.4°C to 16°C during the 41 years period (1970-2010). The analysis reveals that due to dry up of rivers and discharge of groundwater level for irrigation, temperature increased and groundwater level decreased. Hydrographically it is also seen the close relationship between groundwater level and rainfall from the time series analysis. It is observed that temperature is increasing with time and groundwater level is decreasing with time. Here it is found a reverse relationship between groundwater level and temperature. But if open pit coal mine will be done in that area, this will abruptly change the water table, because total water of mine area has to be pumped out. As a result, drying up of wells, reduction of water in streams and lakes, deterioration of water quality, increased pumping costs and land subsidence will occur around the mine. For qualitative analysis four water san1ples out of eight showed high contamination level (Cd > 3) ranging between 4.613- 8.619 (6.6), two samples showed medium contamination level (Cd 1-3) ranging between 2.171-2.785 and two samples showed the low contamination level (Cd <1) ranging between 0.506-0.952 value before mining activities. After mining activities, the predicted concentration index for groundwater samples will show the very high contamination level (Cd > 3) ranging between 155.868- 1627.256. Before mining activities Cd ranged between 0.51 -8.62 and HPI ranged between 2.04-4.42, but after mining activities Cct values are expected to be 155.86 - 1649.7 and HPI ranges between 22.53-204.58. The DRASTIC vulnerability index is computed for evaluation of three conditions (conventional DRASTIC, Modified DRASTIC-CctHPI for before and after mining activities). For conventional DRASTIC the vulnerability index is found ranging from 81-167 of which 31 % area is highly vulnerable. Before mining activities, the vulnerability index was found ranging from 87 -182 of which 3 0% area was highly vulnerable but after mining activities the vulnerability index will be found ranging from 185 - 375 of which 24% area will be highly vulnerable, 35% will be very highly vulnerable and 41 % will be extreme vulnerable. Groundwater, temperature and rainfall were analyzed by following fitting of straight line by least square method. Selected eight heavy metals were analyzed using AAS. The prediction is done by following the data of Raniganj coal field, Maharashtra coal fired power plant in India and Poltegor coalmine, Poland. Two methods such as contamination index (Cct) and heavy metal pollution index (HPI) were used to evaluate the contamination levels. The software used for this study are Arcview 3.3 for the preparation of location map and DRASTIC vulnerability maps. Surfer software were used for 3D groundwater level map and Rockware were used for analysis of lithology and stratigraphy of the study area. The groundwater vulnerability assessment was done using DRASTIC model in GIS environment.