The technology of managing underground water is simple yet intelligent and adopting it will not just help good mining in Bangladesh, but also improve the depleted water tables of Dhaka and save the city from an impending disaster.

Germany's largest coal mining and power company RWE systematically pumps out 550 million cubic meters of water from underground at places where it would start open-pit mining in the near future. This ensures a clean and safe mining--but it also makes the land so dangerously dry that the nearby underground water tables start depleting. It can hurt agriculture and drinking water.

That is why the RWE does not waste this water like the Barapukuria Coal Mine and power companies, which pump out 22 million cubic meters of water annually and waste it entirely in the most polluted form. Consequently the villagers around the Barapukuria mine area are deprived of fresh drinking and irrigation water.

The Barapukuria coalmine was originally designed to extract 60 million tonnes of coal in 30 years but due to a flaw in assessing the water reservoir beneath the ground, the mine was flooded in 1998. This forced the mine authorities to revise the mining plans, which drastically reduced the forecasted production to 30 million tonnes in 30 years. Despite this, the water situation at the mine remained unmanageable and the mine authorities now say that 21 million tonnes of coal would be extractable in 30 years.

In a stark contrast, the RWE annually pumps back 50 million cubic metres (mcm) of water back into the underground-water reservoir through simple, cheap and effective infiltration wells. This ensures that the ground water table is not depleted in a way that nature cannot adequately replenish with water. The farmlands are happy and the nature in the mining area is bustling with trees.

The RWE also supplies 40mcm of water annually to the communities in the 282sqkm North Rhine Westfalia (NRW) coal mining zone of Germany, sends another 60mcm water to the highly-sensitive local wetlands, 170mcm to the power plants that generate 11,000 megawatt (MW) power and the remaining to the lakes and the local rivers.

The Daily Star correspondent visited the mines and coal power plant installations near Cologne at the invitation of Asia Energy Bangladesh between July 25 and July 28. The Daily Star funded the trip and stay of its correspondent, while Asia Energy--that has stakes in the Phulbari Coal Mine--facilitated the visit in collaboration with Germany's biggest mining and power company RWE.

The RWE is a consultant company for Asia Energy for handling Phulbari project's most sensitive area--water tables. The Asia Energy had proposed pumping out 180mcm of water annually in Phulbari to produce 15 million tonnes of coal (Barapukuria producing only half a million tonnes of coal); one third of it will be pumped back into the ground, one third to 1,000MW power plant and the rest for serving the community.

The RWE operates three large lignite coalmines in the NRW area and annually produces 100 million tonnes. This home-grown company takes responsibility for addressing environmental, agricultural and human settlement issues and has developed many technologies over the years.

"The RWE now has 20 to 30 years of experience of de-watering. The idea of de-watering came after the 50's with the advent of technology and mining needs," says RWE's senior hydro-geologist Dr Thomas Von Schwarzenberg. "We have invested 60 million Euros for installing 1,400 wells and we have spent 120 million Euros for their operation. The cost of this water comes at 0.18 cents per cubic meter," he said.

Schwarzenberg notes that the company is legally bound to protect the local wetland, which is located at least 20km off any of the mines. The RWE not only pumps water to this wetland directly, but it must also pump in water underground to keep the water tables healthy enough. A monitoring group measures the water level of the wetland. If it detects a drop in the water level by even a few millimetres, the RWE must act instantly.

The RWE has built 130km of water pipeline, 14km of water infiltration ditches, 150 supporting barriers, 50 direct water rechargers and 175 infiltration wells.

Pumping out of huge water also causes land subsidence. In the NRW area, there had been maximum land subsidence of 4 metres due to de-watering.

HOW WATER IS PUMPED BACK UNDERGROUND

Schwarzenberg showed this correspondent how water is pumped back into the underground reservoir using simple yet intelligent technology--infiltration wells and ditches.

The topsoil of the land that grows trees retains water. As a result rainwater cannot recharge a depleting sub-soil water level. Similarly, the topsoil retains river water or ponds.

Beneath this level of soil is the sand and silt zone, which easily absorbs water and sends it to the water reservoir beneath.

The RWE's infiltration wells are dug like a traditional well through this topsoil, which may be typically 20-30 feet deep. Once the well hits the sand zone, it fills up the well with sand. When water is poured, this sand absorbs it instantly and sends it to the sub-soil water reservoir. Schwarzenberg showed that such a well could pump in millions of cubic metres of water every year.

Schwarzenberg who had visited the Barapukuria coalmine area in the recent past notes, "The Barapukuria water tables can be recharged easily by making such infiltration trenches."

This method can also greatly help fast recharging Dhaka's water tables during the rainy seasons, geologists say.

Dhaka Water and Sewerage Authority (Wasa) says Dhaka's underground water table is depleting by five feet every year, while the city of 10 million people is consuming 75,000 litres of water per second using a total of 2,500 deep tube-wells (Wasa owns 800 to 1,000 deep tube-wells). The present sub-soil water level of Dhaka is at a depth of 210 feet at its highest level, which used to be less than 50 feet two decades ago.

The Bangladeshi topsoil (called Modhupur Clay Layer) is 10 feet to 45 feet deep. Beneath it lies sand and silt zone (called Dupi Pila). Infiltration wells can be dug at a very cheap cost and these could greatly speed up the water recharge system.