Use Of Hydrogen Isotopes In Ground-Water Studies
- Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons.
- Natural isotopes
- Synthetic isotopes
Stable oxygen and hydrogen isotopes have been used in ground water studies to investigate – recharge, mixing, ground water/surface water interaction, advective-diffusive transport,paleohydrogeologic interactions and to estimate ground water ages.
Flow Regime at Wellhead
- As issues of source water protection of drinking water supplies have come to the forefront, the methodology to effectively manage semi-confined aquifers is still unclear.
- Commonly, the area around the wellhead is considered the most risk sensitive area, but in semi-confined settings the most sensitive areas may be located some distance away from the wellhead.
- Confined aquifers are typically less susceptible to anthropogenic contamination than unconfined aquifers;
- however, their vulnerability should not be ignored due to the fact that confined aquifers are not always perfectly isolated systems.
- Aquitard windows, regions of focused recharge through an aquitard, can provide a direct conduit for potential contaminants from anthropogenic sources and elevated risk in otherwise confined hydrogeologic settings.
Tracing Of Water Movement In The Unsaturated Zone Using Stable Isotopes Of Hydrogen
- The model adequately represents experimental observations of isotope profiles during evaporation from saturated or unsaturated soils, under both non-isothermal and non-steady conditions.
- Groundwater replenishment occurs by both indirect (or localized) recharge through streambeds, depressions, etc., and direct (or local) recharge through the surfacial materials.
- It is this latter form of recharge which often leads to a difference in the isotopic signature between rainfall and the unconfined groundwater.
Case study: Comparison – 3H balance and displacement methods
Managing water resources using isotope hydrology
- Of all the water on Earth, only 2.5 per cent is freshwater, the rest is salty. Of this freshwater, most is frozen in icecaps present as soil moisture, or inaccessible in deep underground aquifers, leaving less than 1 per cent accessible for use.
- It is estimated that more than one third of the global food production is based on irrigation, a significant portion of which may rely of unsustainable groundwater sources.
- Isotope hydrology is a nuclear technique that uses both stable and radioactive environmental isotopes to trace the movements of water in the hydrological cycle.
- Isotopes can be used to investigate underground sources of water to determine their source, how they are recharged, whether they are at risk of saltwater intrusion or pollution, and whether they can be used in a sustainable manner.
- During evaporation and condensation, the concentration of oxygen and hydrogen isotopes in a water molecule undergoes small changes.
- When water from the ocean evaporates, the heavier isotopes will condense first and fall as rain before the lighter ones.
Ground Water Dating
The residence time of groundwater in an aquifer or the groundwater age is an important parameter in any palaeo-hydrologic and geo-hydraulic study.
Water-rock interactions occur during groundwater recharge within days/ weeks and during flow in the aquifer within years to even millions of years. Isotope hydrological studies give at least an idea about approximate ages of the various ground waters.
- van den Akker, C. T. Simmons, J. L. HutsonThe use of stable isotopes, deuterium and oxygen – 18 to derive evaporation from flood irrigation on the basis of pan evaporation techniques Journal of Irrigation and Drainage Engineering. Submitted July 5, 2010; accepted February 23, 2011; posted ahead of print March 4, 2011. doi:10.1061/(ASCE)IR.1943-4774.0000361 Stephanie S. Ivey, M.ASCE1; Randall W. Gentry, M.ASCE2; Dan Larsen3; and Jerry Anderson, F.ASCE4, Inverse Application of Age-Distribution Modeling.
Using Environmental Tracers 3H/3He( 1002 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / NOVEMBER 2008) Downloaded 13 Sep 2011 to 18.104.22.168. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org
Maloszewski, P. and Zuber, A., 1993. Principles and practice of calibration and validation ofmathematical models for the interpretation of environmental tracer in aquifers. Advances in Water Res., 16: 173-190.
Libby, W.F., 1953. The potential usefulness of natural tritium. Proc. Nat. Acad. Sci., 39: 245-247.