Hydrogeological environment not favourable for open pit mining

Asia Energy proposed to extract about 10-15 million tons of coal from Phulbari coal field adopting open-pit mining from final depth of 250 to 300 meters by removing 4400 million tons of overburden (rock, sand, mud, soil) covering an area of about 5.2 sqkm throughout the life of the mine i.e. 36 to 38 years. Mining operations will mainly consist of dweatering of aquifer, cleaning and top soil stripping, overburden removal, rehabilitation of mined out areas and overburden dumps. Coal seams (upper and main) ranging in total thickness between 20 and 65 meters are planned to be extracted. Aquifer dewatering will be continuous throughout the operation life of the mine.
Asia Energy assessed that a large quantity of groundwater ranging from 400 to 800 MnL/day will need to be discharged throughout the life of the mine i.e. 36-38 years. It plans to make discharged groundwater available to the tune of 100 to 230 MnL/day for riparian use, river discharge purpose and water for coal fired power station. Of the removable 4400 million cubic meters of overburden, 30 percent will be dumped ex-pit and the remainder deposited back into the pit. According to Asia Energy, the mine would displace 40,000 people of some 100 villages and a portion of Phulbari town. To maintain dry working condition in open-pit mine, aquifers need to be depressurised. Due to mine dewatering activities water level drawdown will lead to water level decline in excess of 10 km from the mine. This would reduce groundwater availability of Phulbari township, surrounding villages and local farming communities within the given area of influence. This will also impact on bio-diversity, wetlands and rivers in the surrounding areas.
Impact on hydrogeological environment
Potential and major groundwater reservoir of Bangladesh lies in its north-western region covering greater Dinajpur and Rangpur districts. The groundwater resource of this region is the main aquifer of Bangladesh which is about 80-120 meters thick in the DupiTila formation and situated at about 10-12 meters below the surface. A study by School of Environmental Studies, Jadavpur University, Kolkata and Dhaka Community Hospital (DCH) on "Possible Arsenic Contamination Free Groundwater in Bangladesh" reveals that groundwater of north-western region of Bangladesh is almost arsenic-contamination free. It runs low in the region during dry season and makes it difficult for the tube wells to draw water. The government and non-government organisations have been trying with tree plantation for many years to prevent desertification in the region.
The underground water level in eight districts of the northern region including Dinajpur is falling gradually posing a threat to Irri-Boro farming. About 30 percent tube wells in the area have become inoperative for declining underground water level. The badly affected districts are Dinajpur, Thakurgaon, Kurigram, Rangpur, Lalmonirhat, Nilphamari and Gaibandha.
According to an NGO consultancy firm the northern region has the possibility of turning into a desert if water is lifted from underground level in excess of 15,000 cusecs a year. But at present about one lakh cusecs of water is being lifted for irrigation which is alarmingly higher than the red mark. Most alarming is that the lifted water is not being proportionately compensated by regular seasonal rainfall. This maximum gaps may cause natural disaster at any time as cautioned by the experts.
Extraction of Phulbari coal adopting open-pit mining method can be disastrous for the north-western region in particular and Bangladesh in general due to dewatering of arsenic contamination free source of drinking and irrigation groundwater from DupiTila formation from a depth of 250 to 300 meters to the tune of 800 million liters per day over a period of 38-years. Dewatering in the Phulbari mining area may not only disturb but also damage the aquifer, making the area a desert like place.
Prof. Nazrul Islam of Department of Geography and Environment at Dhaka University says Dhaka WASA should avoid groundwater extraction and search for surface water sources in order to save groundwater environment. Groundwater extraction alone poses a grave threat to land subsidence with a potentially negative impact like that experienced in countries like Thailand and Mexico, he said. "Two decades ago land subsidence of few inches took place every year in those countries due unbridled groundwater extraction." While the benefits remain uncertain, the results to the environment could be seriously harmful, he explained. "The initiative to set up 1000-ft deep tube wells in Dhaka city is very destructive since existing 600-ft deep tube wells have already created a large vacuum within the underground level due to lack of water recharge, making the situation very vulnerable to earthquakes," he asserted. Extraction of huge quantity of groundwater at Phulbari coal basin can thus put the region to the threat of land subsidence, land sliding and earthquake. Re-injection of only 25 percent of extracted toxic and contaminated water, as per Asia Energy, will not change the situation.
Access to safe water is a fundamental human need and a basic human right. We need to safeguard the supply of pure water and ensure that everyone has excess to it. The right to water has been accepted as a natural, social fact, governments and corporations cannot alienate people from it. Water right comes from nature and creation, not from the rules of the market. We have no right to deny Phulbari People's right of access to water for coal. Water is no less important than oil, gas and coal.
According to Asia Energy, the top-soil will be removed and preserved once mining operation begins in a particular block. This top-soil will be brought back and spread on the top of the area after completion of mining at the particular block which may take 3-5 years. It will be very difficult to preserve top-soil for such a long time. Top-soil may be washed away during monsoon. At least 3-5 monsoons will be there before top-soil is used at the top of the filled out mining block. And the fertility of the top-soil will also be lost during these 3-5 rainy seasons.
During monsoon, already mined out area will be filled up by rain water, which is required to be pumped out again. During rainy season mining will be difficult and may have to be postponed to facilitate pumping of water out of the mine. Thus 2-3 months in a year may be lost due to this. Thus uninterrupted supply of coal to the power station and other coal consumers may not be possible.
Barapukuria coal mine
M/s Wardell Armstrong, a very reputed mining exploration and consulting company of UK, conducted techno-economic feasibility study of Barapukuria coal deposit during 1987-1991. They strongly rejected the idea of open-pit mining at Barapukuria. They estimated removal of 8,000-10,000 litres of groundwater per second for the whole operational life of the mine (30 years) to dewater DupiTila aquifer for open-pit mining at Barapukuria. They realised that the huge extraction of groundwater for such a long time from DupiTila aquifer may damage the most potential and major aquifer in the whole region. This is one of the reasons that M/s Wardell Armstrong opted for underground mining at Barapukuria. 35-40 percent coal can be recovered by adopting underground longwall mining method which is being practiced in most parts of the world.
Present 7 to 8 percent recovery from Barapukuria Coal Mine is not the fault of underground mining method. It is perhaps the fault of mine designer, mine builder, mine developer and mine operator. Therefore, present low recovery at Barapukuria cannot be cited as a supportive example for open-pit mining at Phulbari.
Conclusion
The government may undertake a detail hydrogeological study on major and potential aquifer in the north-western region of Bangladesh in the light of Asia Energy's proposal for open-pit coal mining at Phulbari. At the same time Asia Energy may give a second thought to their proposal and examine underground mining prospects at Phulbari. Adopting underground longwall mining method 35 to 40 percent coal recovery is very much possible also at Phulbari which can easily meet AEC's requirement to run 1000MW power station there ulbari.
Mr Forrest Cookson, in his article "Dealing with existing coal projects" published in The Daily Star on September 05, 2007 has cautioned the government about the consequences if the Phulbari contact is cancelled. But if Asia Energy's proposal of open-pit mining puts the region in the danger of desertification, earthquake, land subsidence and sliding and other natural disasters, then the government in the interest of the country very rightly ask Asia Energy to revise their proposal i.e. switching over to underground mining.
Engr. A K M Shamsuddin, a petroleum and mining consultant, is former Managing Director, Pashchimanchal Gas Co. Ltd. (PGCL), Petrobangla.