Isotopic And Geo chemical Characteristics Of Groundwater In Islamabad

Abstract

Groundwater (deep and shallow) in Islamabad particularly in the vicinity of Lei Nala was characterized by environmental stable( (813C) and Radioactive (tritium) isotopes as well as hydrogeochemical parameters such as physiochemical (pH, electrical conductivity. total dissolved solid, dissolved oxygen and temperature), major cation (Ca*2, Mg2. Na*1, K*1), anion (NO,1. So,2, CO22, HCO,1. Cr1) and toxic metals (Zn, Cd, Cu, Pb, Ni, Fe, As, Cr and Co). Stable isotope techniques in combination with conventional classical techniques have been applied to the study. Lei Nala was sampled at four (4) different locations, ten (10) shallow groundwater samples (200 feet) and twelve (12) deep groundwater (>200 feet) were collected within the jurisdiction of Islamabad for stable isotope and hydrogeochemical parameters. Physiochemical parameters were measured in situ with the help of portable meters. Water samples for chemical analysis were collected in cleaned plastic bottles as per standard methods. Major cations and anions were analyzed by ICP, HPLC, Spectrophotometer, and titration, Toxic metals were analyzed by Polarograph. Stable isotopes were analyzed by Mass Spectrometer and tritium was measured by liquid scintillation counter. The results of physiochemical parameters of water quality are well within the guidelines/recommended limits as stated by the WHO (World Health Organization), European Union (EU), and Pakistan Environmental Protection Agency (Pak-EPA). CO, are absent in all groundwater samples which indicates the presence of limestone dissolution giving rise to bicarbonate and ultimately Ca-Mg type waters. NO,2 contents in the shallow wells particularly in the vicinity of Lei Nala or waste drains are much higher than the recommended values which indicate infiltration from domestic input. 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, HCOS-type of water predominated with 96.15 % samples. However, there is no significant change in the hydro-chemical facies noticed in the study area, which indicates that most of the major ions are natural in origin. The reason is groundwater passing through sedimentary rocks (most specifically Margalla Hill Limestone) dissolves limestone thus dominating HCO and Ca-Mg facies. Toxic metals results revealed that concentrations of Zn, Cd, Cu, Pb, Ni, Cr, Fe and Co in groundwater samples are well within WHO, EU, and Pak-EPA guidelines for drinking water in all samples except one in which Zn, and Pb were quite high which may possibly due to poor quality pipes used in bore. Arsenic is absent in most of the samples except for two samples. Stable carbon isotope techniques have helped to understand the level and source of contamination in groundwater. The more depleted &"Croic values around -8 to -11 %0 PDB are mainly indicative of inventory of domestic sewage pollution. In present investigation none of groundwater samples indicate significant mixing of domestic waste water (sewerage) and/or septic tank water with the groundwater. As such, this study indicates the potential of 8"3Croic technique in relation to physiochemical techniques for assessment of the sources of pollution. The tritium content of the Lei Nala (8.9 TU) is high. Thus, indicating the mixing of rainwater. Shallow groundwater has tritium values between 7.4 to 8.7 TU which also indicates recharge from rain water however deep groundwater has relatively low tritium values around 6.5 TU showing no recent recharge from rainwater. One of the shallow groundwater samples (IBD13) is very close to Lei Nala, and has a tritium value of 8.7 TU which strongly suggests infiltration from rain and/or from a nearby tributary of Lei Nala. The results of all the analysis show that the wells lying within 20-30 m of Lei have maximum contaminant transport from Lei Nala while those away from Lei Nala are free from any sort of contamination.