Environmental evaluation of surface water sources recharging Rawal Dam- Islamabad

Rawal Dam is fed mainly by Kurang River water and partly by streams emanating from the foothills in Islamabad. In addition to discharge from local spring discharges, these streams/ water courses receive some diverted sewage water and occasionally polluted run-off water (from landfills, agricultural fields and poultry farms) during rainy season. This paper presents chemical, biological and stable isotope analysis of water samples collected from Rawal Lake and streams that recharge the Lake. Chemical analysis includes measurements of conventional physiochemical parameters (temperature, pH, redox, electrical conductivity, total dissolved solids, suspended solids, settable solids, turbidity, dissolved oxygen), major ion analysis in (Na, Ca, Mg, K, Cl, NO/sub 3/, SO/sub 4/, PO/sub 4/, ammoniacal nitrogen, carbonate alkalinity) and toxic metals (Cu, Fe, Cr, Ni, Pb). The biological analysis includes determination of BOD/sub 5/ COD as well as Coliform Bacteria (total and fecal) by membrane filtration technique. Results indicate presence of significant counts of fecal Coliform both in the lake water and the feeding streams. However, after filtration of lake water at the supply point, the Coliform bacteria are completely eliminated by chlorination. Stable Isotope analysis includes mass spectrometric determination of stable isotopes of hydrogen and oxygen in water molecule (referred to as: delta /sup 2/H and delta/sup 18/O values per mill V-SMOW) and stable carbon isotope ratios (referred to as delta/sup 13/C values per mill PDB) in total dissolved inorganic carbon (TDIC). The delta/sup 2/H and delta /sup 18/O analysis of water indicate that Rawal Lake is not a well mixed reservoir. Delta/sup 13/ C/sup TDIC/ values of stream water feeding Rawal Lake are quite distinctive: 5 per mill for Stream-II and -10.4 per mill. PDB for Stream-III. The more depleted delta/sup 13/ C/sub TDIC/ values indicate pollution inventory from domestic sewage inputs in the feeding streams. Delta /sup 13/ C/sub TDIC/ values of top surface waters in Rawal Lake range between -3.1 per mill. PDB to -5.4 mill PDB. The depth waters in Rawal Lake show variation of up to 3 per mill PDB. The more negative delta /sup 13/ C/sub TDIC/ variations with depth indicate that isotopically depleted /sup 13/CO/sub 2/ is being dissolved in the lake bottom water as a consequence of biological decay of organic mater in bottom sediments. The study indicates potential of environmental stable isotope techniques to assess changes in pollution dynamics of drinking water reservoirs due to inventories of pollutants from landfill sites and sewage systems. Studies will help authorities to manage clean drinking water supply in Rawalpindi. (author)