Nitrate contamination of riverbank filtrate at Srinagar, Uttarakhand, India: A case of geogenic mineralization

- Riverbank filtrate in Srinagar highly mineralized compared to the river water.
- Bank filtrate and groundwater in parts of the town have high nitrate contamination.
- Leaching from nitrate-bearing rocks likely responsible for high nitrate in the waters.
- Rare case of nitrate contamination from geogenic mineralization.

SummaryIn place of direct pumping, river bank filtration (RBF) is increasingly being used for collecting surface water for municipal supplies. However, as each site is different, every such scheme needs evaluation and adds to our knowledge about RBF. This work aimed at evaluating the efficacy of a well commissioned in May 2010 on the bank of River Alaknanda in Srinagar (Uttarakhand), India. The well water was monitored for coliform removal and mineral content with reference to the river and surrounding groundwater since the construction of the well. Study showed that the well water is much better in terms of bacteriological quality and turbidity, but is highly mineralized with respect to the river water. The ionic concentrations in the well water were comparable to the groundwater in the region. Stable isotope δ2H and δ18O values, however, showed that the well water is predominantly river bank filtrate. In addition, the water from the well has been containing unusually high concentrations of nitrate (53-138 mg/L)-much higher than permissible limit for drinking water supply while the river water had much lower concentrations (0.3-4.2 mg/L). Investigations were conducted on groundwater, wastewaters, soils, and rocks in the area to identify the source of excess nitrate. The results suggest the occurrence of phyllite and quartzite bedrocks as the origin of nitrate. These findings underline the need for extensive hydrogeochemical studies before designing a RBF scheme.