ABSTRACT
Groundwater is recharged naturally by rain and to a lesser extent by surface water bodies like rivers and streams. The isotopes employed for the purpose are both radioactive and stable in nature, the latter taking a major role compared to the radioactive isotopes owing to their inherent limitations to employ them in open field experiments. The tracer technique based on environmental and radioactive isotopes of water is extensively used to get the point value of recharge in a particular location. Chloride ion is a well known chemical tracer, as it is practically conservative in all environments. The application of its isotope in hydrology is limited thus far because there is no suitable isotope of chlorine for convenient application in isotope hydrology. The isotopes are divided into two groups—stable and radioactive isotopes. Further, based on their origin, they can be classified as environmental and artificial isotopes.
