Water from the city’s polluted “rivers” is seeping into the ground, contaminating borewells, according to a study.
More than 95% of borewell samples from villages along the Arkavati show contamination exceeding prescribed standards for drinking, says a study by the Department of Environment Science, Bangalore University.
The study, published recently in the International Journal of Research and Analytical Reviews, adds to the growing scientific literature that have warned of the continued sewage inflow into the Arkavati and Vrishabhavati, seeping into groundwater.
Nandini N., a professor at BU, along with Raghavendra M., and Kumar M., took 50 groundwater samples — from tubewells, borewells and hand pumps — and tested them against 12 physicochemical parameters. These samples represent 20 villages along the river that courses close to the city.
With the Total Dissolved Solids (TDS) value ranging from 300 to 2,189 milligram per litre, researchers found that 95% of the samples exceeded the acceptable limit of 500 mg/l. If consumed directly, this can lead to gastrointestinal diseases, stated the report.
Similarly, while the total hardness has an acceptable limit of 600 mg/l, the samples had a maximum of 1,390 mg/l.
Nitrates, which are the sign of sewage contamination and agricultural runoff, were found to be in the range of 7.33mg/l to 66.93mg/l, and “most samples” exceeded 45 mg/l set as the acceptable limit for drinking water.
While the contaminants do reduce slightly post-monsoon, when rainwater dilutes domestic and industrial sewage, the research notes that the groundwater quality is extremely hard and highly saline and absolutely unfit for consumption and domestic use.
“In most of these places, they do not treat groundwater before consumption. As sewage flow increases, it will continue to seep into the groundwater. The only way to stop this is through treatment at source itself,” said Ms. Nandini.
Last year, researchers from Trans-Disciplinary University and Manipal University looked at bacterial counts, particularly around the Vrishabhavati and Byramangala lake. Nitrate count was as high as 172 mg/l, while they found that 20.6% of water samples tested complied with World Health Organisation’s permissible limits for E.coli microbial count.
