Geophysical electrical survey for aquifer detection, and carbon footprinting for groundwater abstraction in India

Groundwater in India is a critical resource, particularly in semi-arid regions of the country like Rajasthan. The deteriorated quality of surface water has led to the over-exploitation of groundwater, resulting in the drying up of shallow wells and deepening of groundwater levels. The increasing demand for water and drilling cost for boreholes have generated a prior need for exploration, monitoring, and assessment of groundwater aquifers in water-scarce agriculture-intensive areas. Identifying suitable aquifers is important; however, the emissions associated with the extraction of water from these aquifers should not be overlooked as fuel-aided extraction is a significant source of carbon emissions. A geophysical investigation based on electrical resistivity imaging using the dipole–dipole configuration was conducted in the agricultural belt of Alwar district, Rajasthan to detect aquifer depth and its hydrogeological characteristics. Resistivity survey data indicate the presence of a shallow alluvial aquifer at a depth of 9 m. The resistivity of the aquifer ranges from 15 to 84 Ωm, indicating that the soil is saturated with water in its weathered layer with a thin clay layer surrounding the saturated water zones. The groundwater and surface water represent high chemical variability which depicts that groundwater has deep meteoric percolation and subsurface geology has played a key role in regulating the water quality. Further, it was observed that electric and diesel pumps contribute significantly to carbon footprint with the values ranging from 249 to 1476 kgC/ha-yr and 60 to 266 kgC/ha-yr, respectively. Solar pumps can be a sustainable option to meet the target toward decarbonization with no emissions involved. The study concludes that solar pumping of groundwater is an important intervention for decarbonisation in agriculture sector along with judicious management interventions, improved methods of irrigation, and sustainable use of groundwater to ensure water availability and environmental quality in the region.