Grand entry in nothing good.

1. Radioisotopes in ground
water Studies
SUBMITTED TO:-
Dr. D. K. DEOLIA SIR
SUBMITTED BY:-
PRABAL SHRIVASTAV
GOVT. SCIENCE COLLEGE JABALPURM.P.

2. Introduction
• Groundwateris one of the smallestcomponentsof
the hydrosphere
• Most groundwater is of meteoric, i.e.
atmospheric origin
• Groundwater is also often
withdrawn and industrial use
by extraction
wells. The
for agricultural,
constructing
and study
of the
municipal,
operatin
g
distributio
n
and movement of
groundwater is hydrogeology, also
called groundwater hydrology.

3. Composition of total global
water

4. 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.

5. 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.

6. Isotopes
• Environmental isotopes – unique in
regional studies of water resources.
• Artificial isotopes – effective for
site specification and local
application

7. 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.

8. Radiocarbo
n
• Carbon-
14,
14C
,
or radiocarbon, is a
radioactive
isotope of carbon with a nucleuscontaining6 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.

9. 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.

10. • 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.

11. 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

12. 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.

13. 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

14. 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.

15. 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

16. 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.

17. 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.

18. 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

19. 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.

20. 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
use
d
to
estimat
e
groundwater
recharg
e
method
rates
b
y
determinin
g
the
residence time of different groundwate
r
sample
s
collected at different
depths.

21. 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).

22. 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 αinverse of the flow velocity

23. 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

24. 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.

25. 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

26. 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

27. 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.

28. 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.

29. Referenc
e
• 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.

30. THANK
YOU