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Groundwater over exploitation and depletion in groundwater table in many parts of the World posing a serious problem and there is a pressing need to find out the responsible factors^1-3. In addition to the fall in water table, quality of usable groundwater is also deteriorating due to the natural or anthropogenic contaminations^4-6. Some of the factors for depleting groundwater levels and groundwater quality degradation are ever increasing populations; industrial discharges; surface pavements, deforestation etc are affecting recharge zones and recharge sources of groundwater^7-8. Therefore, identifying, conservation and safeguarding of recharge sources and recharge zones is essential through appropriate measures.

Groundwater gets recharged through precipitation, surface water resources, and irrigation return flows. Recharge primarily depends upon its sources, soil characteristics, surface topography, aquifer depth etc⁹. Deep aquifers are potential sources of groundwater as in most of the places shallow aquifers are either dried up or contaminated¹⁰. Data limitations are there about recharge areas, flows and flow rates of groundwater in deeper aquifers. Groundwater age determination provides useful information to investigate flow and flow rates in deeper aquifers.

Groundwater age dating techniques^11-12provides residence time of groundwater from few years to few thousand of years and help in identifying recharge zones as the age of water in recharge zones will be near to the age of recharging water. Once the water is recharged, the values of the isotopes used for age determination will start decreasing according to the half life. Therefore, the age of the groundwater will increase with the downward movement of water from recharge zone to discharge zone.

Groundwater age has also been encouraged as measures of assessing groundwater quality, its sustainability, renewability, identifying flow systems and paleochannels¹³. Therefore, age dating of groundwater is of immense help in planning of the water conservation and advocating management measures in problematic areas.

References

1. MacDonald A et al. 2016. Groundwater depletion and quality in the Indo-Gangetic basin mapped from in situ observations. Nat Geosci 9:762–766.
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2. Rodell M, Velicogna I, Famiglietti JS, 2009, Satellite-based estimates of groundwater depletion in India. Nature 460:999–1002.
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3. Foster, S., Pulido-Bosch, A., Vallejos, Á. et al. 2018. Impact of irrigated agriculture on groundwater-recharge salinity: a major sustainability concern in semi-arid regions. Hydrogeol J 26, 2781–2791.
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4. Lapworth DJ, Krishan G, MacDonald AM, Rao MS. 2017. Groundwater quality in the alluvial aquifer system of northwest India: new evidence of the extent of anthropogenic and geogenic contamination. Sci Total Environ. 599–600 (2017) 1433–1444.
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5. Krishan, G, et al. 2020. Identifying the seasonal variability in source of groundwater salinization using deuterium excess- a case study from Mewat, Haryana, India. J Hydrol- Reg Stud, 31: 100724 https://doi.org/10.1016/j.ejrh.2020.100724.
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6. Krishan G, et al 2021. Role of Ion Chemistry and Hydro-Geochemical Processes in Aquifer Salinization—A Case Study from a Semi-Arid Region of Haryana, India. Water. 13(5):617. https://doi.org/10.3390/w13050617.
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7. Krishan, Gopal, Sudersan, N, Sidhu BS, Vashisth, Rajesh. 2021. Impact of lockdown due to COVID 19 pandemic on Groundwater salinity in Punjab, India: some hydrogeoethics issues, Sustainable Groundwater Resources Management 7, 27 (2021).https://doi.org/10.1007/s40899-021-00510-2.
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8. Siebert, S., J. Burke, J. M. Faures, K. Frenken, J. Hoogeveen, P. Döll, and F. T. Portmann 2010, Groundwater use for irrigation—A global inventory, Hydrol. Earth Syst. Sci., 14, 1863– 1880.
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9. Krishan, Gopal, Ghosh, NC, Chaudhary, Anju and Singhal, Vikas. 2020. Impact assessment of viaduct construction on groundwater recharge in NCT Delhi. E-journal of geohydrology. 1(1):56-59.
10. Krishan et al., 2021. Expansion of salinization in aquifers of Punjab. Report submitted to Punjab State Farmers and Farm Workers Commission, Punjab. 155pp
11. Lapworth DJ, et al. 2015. Groundwater recharge and age-depth profiles of intensively exploited groundwater resources in northwest India. Geophys. Res. Lett., 42 (18): 7554-7562.
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12. IAEA. 2013. Isotope methods for dating old groundwater. Ed by A. Suckow, P.K. Aggarwal and L. Araguas-Araguas.
13. Ferguson, G., Cuthbert, M., Befus, K., Gleeson, T., Noyes, C., and McIntosh, J. 2021. Renewed thinking on groundwater age, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3479, https://doi.org/10.5194/egusphere-egu21-3479, 2021.
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