Groundwater (deep and shallow) in Islamabad particularly in vicinity of Lei Nala were characterized by environmental stable ( 13C) and Radioactive (tritium) isotopes as well as hydrogeochemical parameters such as physiochemical (pH, EC, TDS, DO and temperature), major cation (Ca+2, Mg+2, Na+1, K+1), anion (NO3-1, SO4-2, CO3-2, HCO3-1, Cl-1) and toxic metals (Zn, Cd, Cu, Pb, Ni, Fe, As, Cr and Co). Piper diagram reveals that Ca-Mg- type of water is dominant in the studied area. The percentage of samples falling under Ca-Mg-type was 53.86 %. For anion concentration, HCO3-type of water...