Application of Environmental Isotope Techniques in Groundwater Study

Kamarudin Samuding, Mohd Tadza Abdul Rahman and Roslanzairi Mostapa Environmental Tracer Application Group, Malaysian Nuclear Agency, Bangi, 43000 Kajang, Selangor, MALAYSIA. Tel: 03-89250510 Fax: 03-89250907 Email: [email protected]

ABSTRACT

The application of environmental isotope as a tracers in groundwater study is presented. The isotope technology is useful tool in determining the groundwater recharge sources, ages of water bodies, the interaction between surface water and groundwater, the source of groundwater contamination, the degree of mixing and for estimating subsurface residence times (Sidle, 1995 and Sidle, 1998). Previous studies have successfully used 13C-DIC, 2H-water and 18O-water measurements of groundwater from landfill monitoring wells to detect leachate influence (Hackley, et al., 1996, North, et al., 2007). The environmental isotopes particularly stables isotopes (18O, 2H and 13C) are measured using Continuous Flow Isotope Ratio Mass Spectrometer (CF-IRMS). Oxygen and hydrogen isotope compositions are expressed as units of parts per thousand or delta per mill (δ ‰) deviation from standard mean ocean water (SMOW). Whilst, 13C of dissolved inorganic carbon (DIC) data analysis reported in δ- notation with regard to National Bureau of Standards (NBS). The precision of the analytical measurement is ±0.05‰, ±1‰ and ±0.1‰ for δ2H and δ18O, and 13C respectively. For the isotope analysis, the samples were measured in triplicates in each analytical run for better results. The usual way to interpret stable isotope data is on a plot of 2H versus 18O from the precipitation isotopes values. In hydrological cycle, precipitation is considered as the input for surface water and groundwater. Hence the importance of establishing Local Meteoric Water line thus establishing weighted mean precipitation was adopted (Ayub, 2005).

These techniques have been used to study the groundwater contamination within the landfill area, riverbank infiltration study as well as to determine groundwater resources. Result from the

2 18 13 landfill site study shows that the d H–H2O, d O–H2O and d C–DIC ranged from +7.70‰ to – 48.57‰, –0.05‰ to –7.56‰ and +10.60‰ to –23.17‰ respectively with unique distinct isotopic signature for some surface waters (leachate and pond) and groundwater. This technique demonstrated the ability to distinguish the leachate impacted water samples compared to the conventional technique and thus can be used in determining landfill leachate contamination. The isotope results also clearly delineated the interconnection, recharge process and transport mechanism of the contaminant between the water bodies particularly during the dry period.

Results from the riverbank infiltration study indicate that the δ2H and δ18O compositions for the groundwater that is closed to the river is relatively depleted and similar to that of the river water. This indicates that infiltrating river water is the main source for the groundwater that is closed to the river especially during high flow conditions. On the other word, recharge of these confined aquifers is currently taking place by direct infiltration through the river. Meanwhile, the isotopic composition of groundwater that is located about 500 m and 700m from the river is relatively enriched and similar to the pond nearby. This can explained that there are interconnection between groundwater and surface water. As a summary, the application of these techniques has shown that they not only confirm the results obtained by classical hydrological methods but as an alternative to provide more information and immediate answers to some hydrological problems.

Keywords: Environmental isotopes, groundwater, surface water, contamination, recharge area

References

North, J. & Frew, R.D. 2007. Isotopic Characterization of leachate from seven New Zealand Landfill. In: Landfill Research Focus. Nova Science Publisher. pp. 199-261.ISBN 1-60021-7753

Hackley, K.C., Liu, C.L., and Coleman, D.D., 1996. Environmental isotope characteristics of landfill leachates and gases. Ground Water, 34: 827-836

Sidle, W.C. 1995. Diagnosis of Ground Water–Surface Water Interactions and Their Impact on Drinking Water Supplies from the Analyses of Oxygen18, Deuterium, and Tritium Isotopic Processes, USDOE/EM Technical Memorandum Report: No.11–27, 25pp.

Sidle, W.C. 1998. Environmental Isotope For Resolution of hydrology problems. Environmental Monitoring Assessment 52: 389-410 Academic Publishers Printed in Netherlands.

Ayub, M.S. 2005. Malaysian Meteoric Water Line: An Input to Isotope Hydrological Studies. MINT R&D.