Water Management in Coal Mining Project: Case Study Phulbari
Posted by phulbarinews on July 12, 2009
Water management is one of the major aspects of coal mining, specially for open pit mines. As Phulbari has been planned for open pit operation, its water management plan is a much discussed about matter. EP’s this issue cover report covers Asia Energy’s prepared detailed management plans for water management with adequate fund allocation and its clear commitment.
There is no arguing about the fact that Bangladesh has good quality coal at open pit mineable depth and has the potential to provide long term energy solution for the country. But the point is how Bangladesh would ensure safe and economic extraction of its coal resource against the experience of Barapukuria underground mine which represents a poor match of mining method for the type of thick coal deposits Bangladesh has. Bangladesh has an estimated reserve of about 2,500-3,000 million tonnes of coal but at mineable depth the amount is not more than 1,500 million tonnes as Jamaganj (>1000 million tonnes) is not considered technically and economically feasible as of today for mining for its greater depth.
This quantity of coal is pretty limited and maximization of resource recovery is a must (wherever possible) to attain long-term energy security for the country. Any wrong decision or selection of wrong mining method without taking into consideration of geological and hydro-geological reality of the coal basins will jeopardize the potentials of this sector. Barapukuria has become a very good example in this regard. Bangladesh can’t afford to leave 90% of its valuable coal resource beneath the ground as wastage only for choosing wrong mining method while the country has been in serious crisis of primary energy fuel.
Asia Energy Corporation (Bangladesh) Pty Ltd, the subsidiary of UK-based GCM Resources plc has proposed to establish and operate an open pit coal mine in Phulbari. Phulbari is one of the most well explored and credibly assessed coal fields in Bangladesh. Geological data revealed that it is the shallowest coal basin and ideal candidate for open pit mining. The proposed mine has the potential to recover more than 90% of the deposit, can deliver much needed coal at affordable prices along with other valuable co-products that will come out only as a process of open pit coal extraction. All the potential impacts associated with open pit mine development have been thoroughly assessed and management plans have been prepared with particular importance on water issues. Many of the Project documents are open for public, uploaded on Project website. It would be worth useful to look into the water management issues of Phulbari Coal Project as water management has been raised as a contentious issue for open pit mine development in Bangladesh.
Dewatering & Open Pit Mining
The overlying or underlying sediment and rocks of coal seams in a coal bearing basin may contain water bearing strata (aquifer). Open pit mine development in such situation requires dewatering and depressurization of the aquifers through continuously pumping out of water to keep the mine pit dry and maintain safe working conditions. This potentially lowers the water table within and outside the mining area and makes water inaccessible for many operational shallow and/or deep tube-wells within the influence area, mostly used for irrigation and domestic purposes. Therefore, efficient water management is a critical issue for the successful operation of an open pit mine as well as to maintain the existing water supply system to the environment and community. Open pit mining operation has been successful in different parts of the world including India, Germany, Australia, Indonesia, Greece, Thailand, USA, South Africa managing the overlying and underlying aquifer systems in complex geological and hydro-geological situations.
Underground water withdrawal is not uncommon in Bangladesh and widely practiced in Phulbari region to meet irrigation and domestic water needs. In Dhaka, some 6,480 million litres of water per day is being extracted from the underground aquifers. There are some 200 functional deep tubewells within 10 kilometres of the Phulbari mine site, and some 15,000 shallow tube-wells (STW). During the dry season, the deep tube-wells alone pump more than 1,000 million litres per day for irrigation purposes. The cumulative volume of groundwater extracted by the shallow tube-wells would be significantly greater (about 1,800 million litres per day) than the deep tube-wells. Barapukuria Power Plant and Barapukuria Mine also withdraw significant amount of water, some 78 million litres and 24 million litres per day respectively.
Hydrogeology of Phulbari
The sediment and rock in Phulbari basin contain both aquifers and aquitards that require dewatering and depressurization for open pit mine development. The main aquifer is the really extensive, Upper Dupi Tila Formation, some 100m thick. It underlies the Madhupur Clay and is the main source of domestic and irrigation water in the Project area.
Water Management Plan
All potential water issues associated with open pit mine development have been thoroughly studied and groundwater model has been developed for the Phulbari Coal Project. A Water Management Plan has been prepared to minimize the impacts of mining operations on the natural water balance of the region and offer benefit to environment and community. It is learned that experts from the vastly experienced and successful coal mining and power company, RWE of Cologne Germany, have checked various water issues especially the proposed water injection program and have been engaged to work with Asia Energy during the early years of the Phulbari Coal Project implementation to make the system full proof. Asia Energy has clearly affirmed its position that they have technical and management skills and commitment to manage all the water issues efficiently and adequate funds have been allocated to ensure it. The water management plan of the Project comprises many components, major issues include:
- Mine water balance
- Dewatering system
- Mitigation works
- On-site mine water management
- Comprehensive water monitoring program
The mine water balance has been based on various climatic and major mine and community water demand operational scenarios over the life of the mine. For community requirements, it considers irrigation, aquifer injection and town and mine potable water demands. A mine water balance is complex.
The flow chart indicates that the Project will have excess water throughout the year. During the wet season excess water will need to be discharged off-site into nearby watercourses. The amount to be discharged is not significant comparing to the bank full capacity of the local river courses. During the dry season, there is sufficient water for:
- Irrigation for agriculture.
- Aquifer injection purposes
- Water supply to Phulbari Township; and
- Water for riparian and downstream irrigation uses.
The groundwater level must be pulled down to create dry conditions in the mining area so that the generally low strength aquifer sequence materials (sands, gravel and clays) can be safely excavated. Mine dewatering is usually undertaken for a variety of geo-technical (material strength considerations), mining and safety reasons. This is a well-proven way to maintain dry working conditions, prevent flooding and ensuring the stability of the mine walls and mine haulage road pavements.
Mine dewatering can be achieved in Phulbari by pumping continuously from a ring of dewatering tube-wells around the mine and on benches, and installing pumps in special sumps on the mine floor to remove any surface water. Computer modeling indicates that some 80 to 100 dewatering tube-wells are required at any one time to cumulatively pump some 6,000 liters/second (L/s) to achieve the target.
Depending on the geological and hydro-geological conditions around the mine site, mine dewatering will induce water level draw-down away from the pit. This may restrict availability of water to the surrounding community for irrigation and household purposes. A number of well-tested mitigation measures have been planned to manage the impacts, to make water available to the impacted community. Asia Energy is confident that the proposed mitigation works (internationally reviewed) will minimize the impacts and will offer benefit to environment and community.
One of the mitigation works planned to control the impact of mine dewatering activities in the Phulbari area is aquifer injection. This involves injecting water from the dewatering operation into the Upper Dupi Tila Aquifer at around 5 kilometers from the pit. This hydrologically isolates the impacts of dewatering within and outside the injection. Experience shows up to 30% of water from the mine dewatering operation can be injected into the aquifer with this system.
Certain geological and hydro-geological criteria are required for the successful operation of an injection system. This includes:
- An really extensive, thick, sedimentary sequence;
- The target aquifer preferably overlain by a confining layer; and
- A simple geological structure.
All factors and criteria are available at Phulbari.
Aquifer injection is a proven technology and has been used successfully in many mining project in the world under strict environmental rules and regulations. For example, over 50 million metres3 of water per year is injected into 70 infiltration trenches and 150 recharge wells to protect wetlands near the Rhenish open cut lignite mines in Germany.
Water Supply for Irrigation
Groundwater is the major source of irrigation water during the dry season and a substantial number of shallow tube-wells used for irrigation purposes will not be functional within the influence area of dewatering operation. Depending on the degree of water level draw-down and distance from the mine, reticulated water will be delivered to affected farmers by large diameter pipelines and trenches/canals from the mine dewatering system; or by construction of new deep tube-wells. Sufficient water is available for the piped delivery system in the dry season (216ML/day) for two irrigated crops, thus allowing three crops per year. Another advantage of this system is that the historical dry season water level decline will be ameliorated close to the injection bore field and shallow tube-wells (STW) will be able to operate for the whole irrigation season.
Water Supply for Domestic & Ecological Uses
Groundwater is also the primary source of drinking water to the rural villages and township and Project must ensure safe drinking water to the affected households. A reticulated water supply system will be developed to supply a portion of water from the mine dewatering operation to the affected households. Deep tube-wells will be installed in isolated villages far off from the mine operation area to source water for reticulated water supply system. This will improve the water supply quality to the affected rural households.
Water may also need to discharge to surrounding water bodies from the dewatering operation to maintain current seasonal water levels and quality. Any surface water pumped from the floor of the mine will be treated to ensure it meets national water quality standards before releasing to the neighboring environment.
On- Site Water Management
The overall water management system philosophy is the preferential release of clean water for direct external use and to re-use treated dirty water on-site for mining purposes. Water released from the mine site will conform to water quality discharge standards. On site water management for the Phulbari mine site comprises the following primary components:
- progressive enlargement and linkage of noise bunds, visual mounds, flood levees and the ex-pit overburden dump around the periphery of the expanding mine;
- in-pit water collection sumps and pump system to remove groundwater seepage and rainfall runoff to treatment/storage ponds
- rainfall runoff collection system from disturbed surface works areas (such as haul roads, ex-pit overburden dump, mine service areas) to detention and sediment basins;
- rainfall runoff collection system from undisturbed and rehabilitated surface works areas for release to watercourses outside mine bund areas;
- collection of drainage seepage from ex-pit overburden dump to treatment facilities;
- collection of sewage and treatment by facultative lagoons, then discharge to local wetland;
- collection of industrial liquid waste in a dedicated oily waste treatment facility;
- preferential re-use of ‘dirty’/treated water for mine purposes (dust suppression, plant wash down, landscape and rehabilitation, coal washery and fire fighting);
- controlled water volume and quality discharge from the site; and
- a comprehensive water monitoring program
Monitoring is the key to assess the impacts of mining operations and appropriate mitigation measures to be implemented to rectify the impacts. Asia Energy has developed a comprehensive monitoring system to monitor dewatering effectiveness, batter stability, aquifer injection performance, water chemistry, off-site discharges etc and to assess the requirement for local and regional mitigation works. A telemetric system for automatic ‘real-time’ measurement of key parameters (water levels around the mine, local and regional impacts; dewatering discharge and water injection volumes; water chemistry; etc) will be installed and operated 24 hours/day. In addition, a regular manual monitoring program will also be operational.
Myths of Desertification Due to Dewatering
Desertification is the degradation of land in arid, semi arid and dry sub-humid areas resulting from various factors including climatic variations and human activities. Phulbari is not located in an arid to semi-arid environment and the concern for desertification doesn’t have any scientific basis. The proposed land clearing and deforestation at Phulbari will temporarily occur but will be progressively replaced by nutrient enriched topsoil and 1,946 hectares of forests. Low salinity irrigation water will be supplied to agricultural land and the Madhupur Clay will support vegetation during the dry season. Desertification does not occur in Dhaka City, where, with similar geology, some 75,000 L/s of groundwater is extracted and water levels have declined in excess of 50m. Signs of desertification do not appear at the Barapukuria Mine nor Power Station nor open lignite mines after 50 years dewatering in Germany. There is no single evidence in the world where desertification happened due to mine dewatering.
Water management is one of the major aspects of Phulbari open pit mining operation. Asia Energy has prepared detailed management plans with adequate fund allocation and has made its commitment clear that the company will deal with care the various water aspects of the Project and its incumbent technical and environmental risks. All management plans prepared for any mining project is a living document as the case with Phulbari and are expected to be continuously reviewed and updated and measures taken accordingly. Despite having a comprehensive water management plan for the Project, people still have concern about the management of various water issues especially mine dewatering issue and its impacts on surrounding environment and community. Besides the Project Proponent, the Government has a role to play to eliminate people’s concern and to assure that all water issues are well addressed and well managed and mining operations are environmentally and socially responsive. An independent monitoring system can be developed with data reviewed by some of Bangladesh’s renowned hydro geologists or by a panel of national and international experts to ensure the impacts of water level lowering are being managed and the benefits of the abundant water supply are being delivered.
Zubayer Zaman: Geologist
Date: 01 July 2009, Bangladesh