Volumetric advance estimation ...

Volumetric advance estimation of the exact quantity of regional groundwater in a region is difficult, and no method is foolproof. Conventionally, studies on regional groundwater systems adopt the approach based on gravity induced flow from high to low hydraulic head. Conventional hydro-geologic characterization methods learn about the aquifer by looking at data from well pumping tests to learn about the porosity, permeability, and other properties of the aquifer. Drawback of conventional methods is that the natural heterogeneities in an aquifer are difficult to characterize without detailed geologic information. Additional data can be gathered only by drilling more wells. Drilling costs are particularly high in an arid region where the water table is sometimes very deep below the surface. Moreover, if the test site is cover several square kilometers, it could necessitate hundreds of drilling sites. However, sometimes in the absence of adequate hydraulic data, it is difficult to estimate key parameters by numerical simulations techniques. Moreover, the water table distribution analyses provide a short-term feature. Modeling can be useful to some extent to estimate GW quantity approximately in the pursuit of sustainable solutions, only if it addresses not only economic efficiency and technical merits, but also the preferences and priorities of stakeholders. The isotope tracers occupy a special place, in this context, since, tracers only can give a detailed direct insight into many of the long-term processes of the water movement and distribution within the hidden groundwater system, in integration with hydro-chemical information, GIS, etc. In India, isotope tracer techniques have been used extensively for over three decades, to study groundwater occurrence, "age", recharge mechanism, flow regime, pathways, stratification, hydrodynamic zones, contamination characteristics, groundwater-surface water interactions, and mixing processes in groundwater system; and has been proved to be quite helpful, through some of the internationally acclaimed case studies.