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radio isotope in ground water study

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preethi durairaj

This document discusses the use of radioisotopes in groundwater research. It begins by providing background on groundwater and then discusses why further research is needed due to poor understanding and management of groundwater resources. It describes how stable and radioactive isotopes can be effective tools for hydrological investigations by helping to study recharge sources and rates, groundwater ages, aquifer interactions, and groundwater quality issues like salinization and pollution. Specific isotopes discussed include radiocarbon, tritium, and environmental isotopes. Applications and current uses in developing countries are also summarized.

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radio isotope in ground water study
Radioisotopes in ground water research SUBMITTED BY PREETHI.K.D 2014602009, I M.Sc. Soil Science
Introduction • Groundwater is one of the smallest components of the hydrosphere • Most groundwater is of meteoric, i.e. atmospheric origin • Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.
Composition of total global water
Reasons for research • There is a lack in comprehensive assessment of the quality and availability of groundwater resource. • Resource is often poorly understood and poorly managed.
Effective tool for research • Stable and radioactive isotope techniques are cost effective tools in hydrological investigations and assessments, and are critical in supporting effective water management.
Isotopes • Environmental isotopes – unique in regional studies of water resources. • Artificial isotopes – effective for site specification and local application
Environmental isotopes Stable isotopes 2H, 13C, 18O Radioisotopes 3H, 14C • SI – measured by isotope ratio mass spectrophotometer • RI – measured by counting of their radioactive decays.
Radiocarbon • Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. • Carbon-14 was discovered by Martin Kamen and Sam Ruben. • Half life – 5370 years • Beta - 0.156476 MeV • Radiocarbon dating is a radiometric dating method that uses (14C) to determine the age of carbonaceous materials up to about 60,000 years old.
SAMPLING PROCEDURES There are two techniques used in radiocarbon dating: (1) the radiometric technique for normal size samples, which counts the beta radiation coming from a prepared material, and (2) the AMS (Accelerator Mass Spectrometry) technique, which is suited for very small amounts of samples. Beta Analytic Inc. uses the AMS technique.
• For ground water dating, the AMS technique is most common due to the reduced physical labor for the collection of the sample in the field and, afterwards, the laboratory. • With a sample sent for AMS dating, we need one liter of the well water. • A standard wide-mouth plastic bottle available in all chemical supply firms is generally used. • Please note that the persons sampling the well or working in the laboratory should not be wearing luminous watches - this can cause tritium contamination.
Radiocarbon The basic radiocarbon age determination calculation is as follows: t = - 8035 ln (δC14final / δC14initial ) • t = the radiocarbon age of the sample • 8035 = the decay constant of radiocarbon, i.e., the half-life divided by ln 2. A half-life of 5730 years for carbon 14 is used, as per international convention • ln = the natural logarithm • δC14final = the measured net radiocarbon content of the sample • δC14initial = the net radiocarbon content of the modern standard
Tritium • Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays. • Tritium (3H), and other chemical and isotopic substances in ground water, can be used to trace the flow of young water (water recharged within the past 50 years) and to determine the time elapsed since recharge. • Information about the age of ground water can be used to define recharge rates, refine hydrologic models of ground- water systems, predict contamination potential, and estimate the time needed to flush contaminants from ground-water systems.
Cont.. • In water it is expressed in TU • Half life – 12.43yr • Concentration is generally low in natural water • Electrolytic enrichment is often carried out prior to decay counting using liquid scintillation or proportional counters. • In precipitation – 2 to 5 TU
Cont… • It is difficult to evaluate age information from tritium data alone, age commonly can be reliably determined from data on tritium (3H) and its decay product, helium-3 (3He). • The 3H/3He age is based on a calculation that determines the amount of 3He derived from radioactive decay of 3H in the water. • Several conditions are necessary to solve the calculation and interpret the age: (1) The sample must contain detectable 3H (greater than approximately 0.5 tritium unit, or TU, which is defined as one 3H atom in 1018 hydrogen atoms) and (2) if the sample contains terrigenic helium from the Earth’s crust and mantle sources, the relative abundances of helium-3 and helium-4 isotopes in the terrigenic helium must be known, and data on dissolved neon concentrations in the sample are needed to help determine how much helium-3 is derived from tritium decay.
Tritium dating • In principal, the determination of the tritium/3He age of groundwater is simple. If both the tritium and 3He concentrations are measured in TU, it can be calculated as
Tritium dating • Tritium (H-3) dating of ground water is sometimes used as ancillary data for the radiocarbon dating study. It is less successful than radiocarbon dating for two reasons: • (1) the half-life of tritium is merely 12 years (versus approximately 5568 years for radiocarbon), meaning that only young ground water would show measurable values, and • (2) the contamination of the atmosphere with nuclear testing fallout tritium was extensive, reaching thousands of times the normal amount, resulting in a serious ambiguity.
Applications Isotopes are commonly employed to investigate: • sources and mechanisms of groundwater recharge • groundwater age and dynamics • interconnections between aquifers • interaction between surface water and groundwater • groundwater salinization and • groundwater pollution.
Source and mechanism of groundwater recharge • To ensure the sustainable development and management of groundwater resources. • Isotopes - used to identify and evaluate present day groundwater recharge
Groundwater recharge • The isotopic composition of groundwater (oxygen-18 and deuterium) is determined by the isotopic composition of recharge. • If most of the recharge is derived from direct infiltration of precipitation, the groundwater will reflect the isotopic composition of that precipitation • Differences in isotopic composition of groundwater resulting from different recharge sources, there can be differences due to how recently recharge occurred.
Cont… • It is possible to identify, quantify, modern recharge — within 40 to 50 years — by measuring isotopes and dissolved gases (e.g. tritium, tritium and helium-3, chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF6)) in soil water in an unsaturated zone or in groundwater from shallow. • The tritium–helium-3 method used to estimate groundwater recharge rates by determining the residence time of different groundwater samples collected at different depths.
Recharge rate determination by tracer peak displacement • The assumption of the piston-flow model is that the tracer and all water in the soil move simultaneously. • The tracer peak at the position z and the time t is the integrated result of the downward (infiltration) and upwards (evaporation) movement that occurred during the period t – to (to — starting time). • The amount of water stored in the soil section between z and zo represents the actual recharge (or the actual evaporation loss if z is above the initial position zo).
Groundwater age • Residence time, also called groundwater age, is the length of time water has been isolated from the atmosphere. • unconfined aquifers – a vertical gradient of groundwater ages (increasing age with depth). • Gradient α inverse of the recharge rate (volume/time) • confined aquifers – horizontal or lateral gradient (age increasing with distance from area of recharge). • Gradient α inverse of the flow velocity
Cont… • Groundwater movement – few meters per yr • Km/yr - hundreds or thousands of years old In large aquifers with long flow paths : • carbon-14 (5730 years ) - a suitable tool for the dating of groundwater in an age range of about 2000 to 40,000 years. In deep confined aquifers : ages of tens and even hundreds of thousands of years •krypton-81, chlorine-36 and iodine-129
Interconnections between aquifers • stable isotopes, can be used to investigate such interconnections (isotopic composition of groundwater in the aquifers being measured is different.) • Stable isotope data can be used to estimate the flow of groundwater from adjacent aquifers.
Interaction between surface water and groundwater • Groundwater often consists of a mixture of recharge from surface water (lakes or rivers) and local precipitation. • A simple isotopic balance equation can then be used to estimate the relative proportions of surface water and precipitation in recharge
Groundwater salinization In areas where salinization of groundwater is occurring, it is necessary to identify the mechanism of salinization in order to prevent or alleviate the cause. Isotope techniques can be used to distinguish the importance of the following processes which may lead to the salinization of groundwater: • leaching of salts by percolating water • intrusion, present or past, of salt water bodies such as sea water, brackish surface water or brines and • concentration of dissolved salts through evaporation
Groundwater pollution • Environmental isotopes can be used to trace the pathways of pollutants in aquifers and • predict spatial distribution and temporal changes. • Concentration and stable isotope composition of hydrocarbons – a powerful tool for pollution assessment and remediation.
Current use • The isotope hydrology program at the International Atomic Energy Agency works to aid developing states (including 84 projects in more than 50 countries) and to create a detailed portrait of Earth's water resources. • In Ethiopia, Libya, Chad, Egypt and Sudan, the International Atomic Energy Agency used such techniques to help local water policy deal with fossil water. • An arsenic pollution crisis in Bangladesh that the World Health Organization calls the "largest mass poisoning of a population in history" has been investigated using this technique.
Reference • www.iaea.org • www.iisc.ernet.in • www.ijird.com • Bohlke, J.K., and Denver, J.M., 1995, Combined use of groundwater dating, chemical, and isotopic analyses in two agricultural watersheds, Atlantic coastal plain, Maryland: Water Resources Research, v. 31, p. 2319–2339.
Thank you

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radio isotope in ground water study

  • 2. Radioisotopes in ground water research SUBMITTED BY PREETHI.K.D 2014602009, I M.Sc. Soil Science
  • 3. Introduction • Groundwater is one of the smallest components of the hydrosphere • Most groundwater is of meteoric, i.e. atmospheric origin • Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.
  • 4. Composition of total global water
  • 5. Reasons for research • There is a lack in comprehensive assessment of the quality and availability of groundwater resource. • Resource is often poorly understood and poorly managed.
  • 6. Effective tool for research • Stable and radioactive isotope techniques are cost effective tools in hydrological investigations and assessments, and are critical in supporting effective water management.
  • 7. Isotopes • Environmental isotopes – unique in regional studies of water resources. • Artificial isotopes – effective for site specification and local application
  • 8. Environmental isotopes Stable isotopes 2H, 13C, 18O Radioisotopes 3H, 14C • SI – measured by isotope ratio mass spectrophotometer • RI – measured by counting of their radioactive decays.
  • 9. Radiocarbon • Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. • Carbon-14 was discovered by Martin Kamen and Sam Ruben. • Half life – 5370 years • Beta - 0.156476 MeV • Radiocarbon dating is a radiometric dating method that uses (14C) to determine the age of carbonaceous materials up to about 60,000 years old.
  • 10. SAMPLING PROCEDURES There are two techniques used in radiocarbon dating: (1) the radiometric technique for normal size samples, which counts the beta radiation coming from a prepared material, and (2) the AMS (Accelerator Mass Spectrometry) technique, which is suited for very small amounts of samples. Beta Analytic Inc. uses the AMS technique.
  • 11. • For ground water dating, the AMS technique is most common due to the reduced physical labor for the collection of the sample in the field and, afterwards, the laboratory. • With a sample sent for AMS dating, we need one liter of the well water. • A standard wide-mouth plastic bottle available in all chemical supply firms is generally used. • Please note that the persons sampling the well or working in the laboratory should not be wearing luminous watches - this can cause tritium contamination.
  • 12. Radiocarbon The basic radiocarbon age determination calculation is as follows: t = - 8035 ln (δC14final / δC14initial ) • t = the radiocarbon age of the sample • 8035 = the decay constant of radiocarbon, i.e., the half-life divided by ln 2. A half-life of 5730 years for carbon 14 is used, as per international convention • ln = the natural logarithm • δC14final = the measured net radiocarbon content of the sample • δC14initial = the net radiocarbon content of the modern standard
  • 13. Tritium • Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays. • Tritium (3H), and other chemical and isotopic substances in ground water, can be used to trace the flow of young water (water recharged within the past 50 years) and to determine the time elapsed since recharge. • Information about the age of ground water can be used to define recharge rates, refine hydrologic models of ground- water systems, predict contamination potential, and estimate the time needed to flush contaminants from ground-water systems.
  • 14. Cont.. • In water it is expressed in TU • Half life – 12.43yr • Concentration is generally low in natural water • Electrolytic enrichment is often carried out prior to decay counting using liquid scintillation or proportional counters. • In precipitation – 2 to 5 TU
  • 15. Cont… • It is difficult to evaluate age information from tritium data alone, age commonly can be reliably determined from data on tritium (3H) and its decay product, helium-3 (3He). • The 3H/3He age is based on a calculation that determines the amount of 3He derived from radioactive decay of 3H in the water. • Several conditions are necessary to solve the calculation and interpret the age: (1) The sample must contain detectable 3H (greater than approximately 0.5 tritium unit, or TU, which is defined as one 3H atom in 1018 hydrogen atoms) and (2) if the sample contains terrigenic helium from the Earth’s crust and mantle sources, the relative abundances of helium-3 and helium-4 isotopes in the terrigenic helium must be known, and data on dissolved neon concentrations in the sample are needed to help determine how much helium-3 is derived from tritium decay.
  • 16. Tritium dating • In principal, the determination of the tritium/3He age of groundwater is simple. If both the tritium and 3He concentrations are measured in TU, it can be calculated as
  • 17. Tritium dating • Tritium (H-3) dating of ground water is sometimes used as ancillary data for the radiocarbon dating study. It is less successful than radiocarbon dating for two reasons: • (1) the half-life of tritium is merely 12 years (versus approximately 5568 years for radiocarbon), meaning that only young ground water would show measurable values, and • (2) the contamination of the atmosphere with nuclear testing fallout tritium was extensive, reaching thousands of times the normal amount, resulting in a serious ambiguity.
  • 18. Applications Isotopes are commonly employed to investigate: • sources and mechanisms of groundwater recharge • groundwater age and dynamics • interconnections between aquifers • interaction between surface water and groundwater • groundwater salinization and • groundwater pollution.
  • 19. Source and mechanism of groundwater recharge • To ensure the sustainable development and management of groundwater resources. • Isotopes - used to identify and evaluate present day groundwater recharge
  • 20. Groundwater recharge • The isotopic composition of groundwater (oxygen-18 and deuterium) is determined by the isotopic composition of recharge. • If most of the recharge is derived from direct infiltration of precipitation, the groundwater will reflect the isotopic composition of that precipitation • Differences in isotopic composition of groundwater resulting from different recharge sources, there can be differences due to how recently recharge occurred.
  • 21. Cont… • It is possible to identify, quantify, modern recharge — within 40 to 50 years — by measuring isotopes and dissolved gases (e.g. tritium, tritium and helium-3, chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF6)) in soil water in an unsaturated zone or in groundwater from shallow. • The tritium–helium-3 method used to estimate groundwater recharge rates by determining the residence time of different groundwater samples collected at different depths.
  • 22. Recharge rate determination by tracer peak displacement • The assumption of the piston-flow model is that the tracer and all water in the soil move simultaneously. • The tracer peak at the position z and the time t is the integrated result of the downward (infiltration) and upwards (evaporation) movement that occurred during the period t – to (to — starting time). • The amount of water stored in the soil section between z and zo represents the actual recharge (or the actual evaporation loss if z is above the initial position zo).
  • 23. Groundwater age • Residence time, also called groundwater age, is the length of time water has been isolated from the atmosphere. • unconfined aquifers – a vertical gradient of groundwater ages (increasing age with depth). • Gradient α inverse of the recharge rate (volume/time) • confined aquifers – horizontal or lateral gradient (age increasing with distance from area of recharge). • Gradient α inverse of the flow velocity
  • 24. Cont… • Groundwater movement – few meters per yr • Km/yr - hundreds or thousands of years old In large aquifers with long flow paths : • carbon-14 (5730 years ) - a suitable tool for the dating of groundwater in an age range of about 2000 to 40,000 years. In deep confined aquifers : ages of tens and even hundreds of thousands of years •krypton-81, chlorine-36 and iodine-129
  • 25. Interconnections between aquifers • stable isotopes, can be used to investigate such interconnections (isotopic composition of groundwater in the aquifers being measured is different.) • Stable isotope data can be used to estimate the flow of groundwater from adjacent aquifers.
  • 26. Interaction between surface water and groundwater • Groundwater often consists of a mixture of recharge from surface water (lakes or rivers) and local precipitation. • A simple isotopic balance equation can then be used to estimate the relative proportions of surface water and precipitation in recharge
  • 27. Groundwater salinization In areas where salinization of groundwater is occurring, it is necessary to identify the mechanism of salinization in order to prevent or alleviate the cause. Isotope techniques can be used to distinguish the importance of the following processes which may lead to the salinization of groundwater: • leaching of salts by percolating water • intrusion, present or past, of salt water bodies such as sea water, brackish surface water or brines and • concentration of dissolved salts through evaporation
  • 28. Groundwater pollution • Environmental isotopes can be used to trace the pathways of pollutants in aquifers and • predict spatial distribution and temporal changes. • Concentration and stable isotope composition of hydrocarbons – a powerful tool for pollution assessment and remediation.
  • 29. Current use • The isotope hydrology program at the International Atomic Energy Agency works to aid developing states (including 84 projects in more than 50 countries) and to create a detailed portrait of Earth's water resources. • In Ethiopia, Libya, Chad, Egypt and Sudan, the International Atomic Energy Agency used such techniques to help local water policy deal with fossil water. • An arsenic pollution crisis in Bangladesh that the World Health Organization calls the "largest mass poisoning of a population in history" has been investigated using this technique.
  • 30. Reference • www.iaea.org • www.iisc.ernet.in • www.ijird.com • Bohlke, J.K., and Denver, J.M., 1995, Combined use of groundwater dating, chemical, and isotopic analyses in two agricultural watersheds, Atlantic coastal plain, Maryland: Water Resources Research, v. 31, p. 2319–2339.