Mariappa, a daily wage worker from Mutharayanapura in Kanakapura taluk, recently made a startling discovery. He found that the 160-foot borewell that irrigated the farm he works on had suddenly gone dry. Groundwater, which had once been in abundance here, was finally struck only at 350 ft. The insatiable demand from Bangalore's construction industry has spawned large-scale illegal sand extraction in this area, which has permanently changed the landscape of scores of villages in Kanakapura and depleted the groundwater here. The cratered terrain may be the most visible impact of this highly water-intensive activity, but it has dealt a serious blow to agriculture. Sand extraction has depleted an important source of irrigation and stripped away vast tracts of fertile topsoil, where ragi, field beans, coconut and mulberry were once cultivated. And now farmers are abandoning agriculture for sand extraction, an activity that may be lucrative in the short term, but one that could, in the long run, bring economic ruin. As riverbed sand has been virtually exhausted, contractors are now turning to agricultural areas as easy sources, an official from the Department of Mines and Geology told The Hindu. "But filter sand cannot be considered sand at all. The grain size and silica content is too small to meet construction specifications. We do not give leases for this form of sand extraction. It violates the Mines and Minerals (Regulation and Development) Act,' he says. According to a study on the impact of sand extraction in agricultural fields around Bangalore, published in Current Science on July 25, every lorry load of sand requires nearly 1,32,000 litres of water, and 120 cubic metres (four tractor loads) of top soil. At a sand-filter here, Kumar (name changed) instructs his employees as they wash down the soil with a generator-powered hose and sieve it to separate the silt-clay from sand. Kumar, once a farmer, says: "There is no money in agriculture any more.' Sand, on the other hand, is profitable business: a truck-load of good quality riverbed sand costs up to Rs. 15,000. Even this low-grade soil that Mr. Kumar has extracted will be sold for Rs. 4,500. If one acre of ragi yields the farmer an annual income of Rs. 5,000, the same land fetches up to Rs. 50,000 an acre per year if leased to a contractor.