A new study has found that 60 percent of the groundwater in the massive Indo-Gangetic river basin, named for the Indus and the Ganges Rivers is contaminated and not fit to drink or use to irrigate crops.
In the study published in the journal Nature Geoscience on August 29, 2016, the authors reveal that to a depth of 200 meters (650 feet), some 23 percent of the groundwater stored in the basin is too salty, and about 37 percent “is affected by arsenic at toxic concentrations.”
The Indo-Gangetic Basin accounts for a quarter of the Earth’s groundwater reserves. Groundwater is freshwater stored underground in crevices and spaces created by soil and rocks, fed by rivers, streams and rainfall.
And while the problem at hand is not one of depletion, the knowledge that some 15 to 20 million wells extract water from the basin every year is raising concerns about future usage. Now the pressing concern is the widespread salt and arsenic contamination.
The study used ground-based data for the period 2000 through 2012, including yearly water-table trends, groundwater abstraction, groundwater chemistry and groundwater storage. In addition, a data set of 3,429 multi-year water-table records was developed.
The research team discovered that in 70 percent of the basin, groundwater levels were rising. Water levels in the remaining 30 percent of the basin, around large metropolitan areas, appeared to be falling, reports The Guardian.
Causes of the contamination
Salt and arsenic can seep into groundwater through natural and man-made causes. The U.S. Environmental Protection Agency (EPA) has set an arsenic maximum contaminant level (MCL) for public water supplies at 0.010 mg/L. This is equivalent to 0.010 parts per million (ppm) in drinking water.
At the present time, the EPA guidance level for sodium in drinking water is 20 mg/L. This takes into account those individuals on a restricted sodium intake of 500 mg/day.
The arsenic found in the basin is most certainly man-made, even though natural levels do occur, the amounts reported by the research team are indicative of fertilizer and mining operations. There has been an arsenic poisoning crisis going on in southern Asia since at least the mid-1970s when water sources changed from surface to groundwater. As more and more wells were dug, the arsenic began accumulating in the deeper confines of the aquifers.
