Integrated hydrogeochemical, isotopic and geomorphological depiction of the groundwater salinization in the aquifer system of Delhi, India. (1st November 2015)

• Record Type: Journal Article
• Authors: Kumar, Manish; Rao, M. Someshwar; Deka, Jyoti Prakash; Ramanathan, AL.; Kumar, Bhishm
• Is Part Of: Journal of Asian earth sciences. Volume 111(2015)
• Page Start: 936
• Page End: 947
• Publication Date: 2015-11-01
• Subjects: Salinization -- Hydrogeology -- Stable isotope -- Tritium dating -- Groundwater -- India; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2015.08.018
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Integrated investigation of salinization using water quality, age and isotopic fingerprinting. Closed inland marine conditions developed in the geological past have led to the salt bed deposition. Anthropogenic activities and evaporative enrichment is increasing the salinity. Salinity flushing is possible and proceeds in the areas with freshwater recharge. Abstract: The problem of salinization in the Delhi aquifer, that currently exhibits rapid landuse change, is conspicuous and severe. Salinization may be caused either by a single process, or a combination of different processes; including anthropogenic related activities, water logging and evaporative concentration of salts, influx of natural saline water, upconing of brines from the deeper parts of the aquifer, and airborne salts depositions. However, there is a lack of well-proven theory that can explain the salinity of the order of 5000 μS/cm in the deeper aquifers of Delhi. This work identifies inconclusiveness in the previous theories of marine ingression, evaporation enrichment and subsequent leaching of salt. Further, the study depicts a conceptual understanding of the origin of salinity in groundwater based on the integrated investigations of groundwater quality, age and stable isotopic fingerprinting as well as GIS based mapping of geomorphic features. In order to explain the salinity observed in groundwater of NCT Delhi, a phenomenological scenario is illustrated and supported by additional evidences. The highest average EC value was for the shallow aquifer and is strongly symptomatic of anthropogenic influences on groundwater chemistry. Piper diagram showed heterogeneous water type and sufficient recharge/mixing of the groundwater from different aquifers. The relationship between Cl − /Br − ratios vs. Cl − indicated dissolution of salt deposits containing evaporative fraction present in the unsaturated zones or in the sediments of deeper aquifers and leaching of evaporative minerals from dunes of the adjacent Thar Desert. Cl − /SO4 2− ratio suggested the presence of connate seawater, halite dissolution and concentration of dissolved salts by evapo-transpiration of river water diverted for irrigation. The results show, that the closed inland marine conditions developed and buried with the active sedimentation in the geological past in this region, and further intensive exploitation of groundwater, and enhanced evaporation have together resulted in saline playa condition in some part of the region. The scenario was further verified by matching the required condition for the formation of salt pan or playa with the existing geo-morphological conditions of the area. Isotopic results indicate that salinity flushing is possible and proceeds in the areas of freshwater recharge.