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'''Arsenic contamination of groundwater''' is a natural occurring high concentration of [[arsenic]] in deeper levels of groundwater. It is a high-profile problem due to the use of deep tubewells for water supply in the Ganges Delta, causing serious [[arsenic poisoning]] to large numbers of people. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water.