Pitfalls of open-pit mining

Underground mining is the best option. Photo: H Arif/ Drik News

Asia Energy proposed to extract about 10-15 million tons of coal from Phulbari Coal Field adopting open-pit mining method from a depth ranging from 250 to 300 metres by removing 4,400 million tons of overburden (rock, sand, mud, soil) covering an area of about 5.2 sq.km.
Mining operations will mainly consist of dewatering of aquifer, cleaning and topsoil stripping, overburden removal, rehabilitation of mined-out areas and overburden dumps.
The geological and hydro-geological environment of Phulbari coal basin is not favourable for open-pit mining, but underground mining method will be technically feasible and economically viable.
The major groundwater reservoir of Bangladesh covers greater Dinajpur and Rangpur districts. The groundwater resource of this region is the main aquifer, which is about 80-120 metres thick in the DupiTila formation and situated about 10-12 metres below the surface.
A study reveals that groundwater level is falling alarmingly in the northern districts. According to an NGO, the northern region may turn into a desert if the amount of water lifted from underground exceeds 15,000 cusecs a year. But about one lakh cusecs of water are being lifted for irrigation. Most alarming is that the lifted water is not being proportionately compensated by regular seasonal rainfall.
Extraction of Phulbari coal adopting open-pit mining method will be disastrous for the north-western region due to dewatering of drinking and irrigation groundwater from DupiTila formation to the tune of 800 million litres per day over 38-years.
Experience shows that over-extraction of groundwater can cause land subsidence and lead to creation of underground vacuums which make us all the more vulnerable to earthquake. Extraction of a large quantity of groundwater at Phulbari will expose the north-western region to the threat of land subsidence, land sliding and earthquake.
According to Asia Energy, the topsoil will be removed and preserved once mining begins in a particular block. It will be preserved before it is brought back and spread on the top of the area filled, and utilised after completion of mining -- which may take 3-5 years.
At least 3-5 monsoons will pass before the topsoil is used at the top of the filled-out mining block. During monsoon, the mined-out area will be filled up by rainwater, which will have to be pumped out. Mining will be difficult and may have to be postponed to facilitate that. Thus 2-3 months in a year may be lost, and uninterrupted supply of coal may not be possible.
About 200,000 people from 150 villages will have to be evacuated from the mine area, and they will be deprived of their livelihood. Asia Energy's proposal to rehabilitate the people phase by phase and block by block in the refilled area cannot be materialised since coal mine regulations prohibit people from living close to an operative mine.
The coal seam lies more than 200 metres below the surface. The overburden of Phulbari coal deposit is unconsolidated and water-logged. Open-pit mining is not practiced below 150-200 metres. The unconsolidated and water-logged bed above the coal seam will cause instability of the working "bench." Installation of heavy equipments will be very difficult in the loose soils at intermediate depth.
Existence of major faults in the Phulbari coal basin indicates presence of a highly disturbed zone. This will facilitate rapid draw-down of the water table, which will disturb the stability of the major aquifer in the region. Major, massive and potential water reservoirs lie above the coal seams, and open-pit mining will damage the major aquifer.
There are agricultural lands, villages, townships, forests, etc. above the coal deposit. Rehabilitation and relocation in a congested area like Phulbari will be very difficult.
Germany is one of the most developed and industrialised nations in the world, while Bangladesh is one of the most thickly populated and least developed countries. The density of population in RWE mining areas vary from 290-529 inhabitants per sq. km., whereas it is about 916 per sq. km. in Phulbari area.
The people of Phulbari area are dependent on their agricultural land while RWE people are not dependent on the land that has been under mining. RWE rehabilitated over 30,000 people in the last 50 years in barren and unused land, whereas about 2,00,000 people from Phulbari area will have to be rehabilitated in 30 years -- mostly in agricultural land or otherwise usable land.
RWE installed 1,400 wells for 100 percent re-injection of pumped out water, while Asia Energy proposes to install 80-100 dewatering tube wells for re-injection of 25 percent of the water. Phulbari coal basin lies beneath a massive and most potential aquifer, whereas RWE mine does not lie beneath one.
Open-pit mining operations causes lowering of the groundwater level, which will ultimately generate acid mine drainage (AMD). Because of large discharge area, only innovative in-situ technology can be used to reduce the AMD.
Such a technology has been developed on a laboratory scale in German and is currently being tested in an aquifer already contaminated by AMD in a bid to assess and improve groundwater quality.
We are not aware of such a bid by Asia Energy in Phulbari. The geological and hydro-geological settings of Phulbari deposit are completely different from RWE deposit. RWE mines were developed by local experts, while the Phulbari mine may be developed by foreign experts.
The present recovery of 7 percent to 8 percent of coal from Barapukuria may be increased to 35 percent to 40 percent if "Hydraulic Stowing" is undertaken. Hydraulic stowing could also minimise the subsidence that occurred at Barapukuria.
If latest underground coal extraction technology is adopted, coal recovery from Barapukuria may rise to 60 percent to 70 percent. Therefore, the present low recovery of Barapukuria coal cannot be cited as a supportive example for open-pit mining at Phulbari.
Initially, BHP Australia discovered Phulbari coal in 1997 after extensive exploration. But, in 1998, BHP assigned the job to a lesser-known company, Asia Energy, and left Bangladesh. BHP probably realised that in a thickly populated country like Bangladesh where coal seam lies beneath three valuable resources -- water reservoir, agricultural land, township and villages -- open-pit mining will be disastrous.
Exploitation of Phulbari coal deposit is a must for Bangladesh to meet the power demand of the country. Therefore, development of the Phulbari coalfield through adopting underground mining method should be immediately undertaken.
Asia Energy may be advised to examine underground mining prospects at Phulbari and submit an underground mining proposal. 35 percent to 40 percent coal recovery is possible at Phulbari through adoption of underground long-wall mining method, which can run a 1,000 MW power station at Phulbari.
Moreover, using present and latest underground mining technology, 60 percent to 70 percent recovery of coal can be made. We don't need to recover 90 percent coal for export. We need to recover for our own consumption as per requirement. That is very much possible adopting underground mining method.
Engr. A.K.M. Shamsuddin is a Petroleum & Mining Consultant. E-mail: [email protected].