Natural radioactivity in groundwater in the Negev Desert and the Arava Valley, Israel

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Natural radioactivity in groundwater in the Negev
Desert and the Arava Valley, Israel
Gustavo Haquin Soreq Nuclear Research Center,
Yavne 81800 ISRAEL
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Introduction

• In the last years high concentration of uranium
  and radium isotopes and radon were measured in
  groundwater from the Nubean sandstone (Kurnub)
  and the upper cretaceous limestone (Judea)
  aquifers in the Negev and the Arava valley.
• As most of the groundwater basins in the Middle
  East are being diminished or contaminated,
  exploitation of the deep aquifers units is
  increasing.
• Objectives of present work
• Mapping the natural radioactivity in groundwater
  in the south of Israel
• Comparison of radium measurement methods
• Understanding the physical and chemical
  processes of radium enrichment in groundwater
• Assessment of the radiological consequences of
  consuming high radium groundwater

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Natural decay series
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(No Transcript)
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Study area
Kurnub aquifer
Group 1 NE Negev - Craters
Group 2 NE Negev Dead Sea
Group 3 South Arava
Group 4 Ashalim
Judea aquifer
Group 5 South and central Arava
Group 6 NE Negev
Group 7 NW Negev
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Processes for radium enrichment in ground water

• Precipitation
• Enrichment of SrSO4 and PbSO4 instead of BaSO4
  atomic radius
• Decrease in radium content in solid with
  increasing temperature
• Adsorption and ion exchange
• Kd increase with time and decrease with T
• Source for decay products flux into water
• Linear correlation between radium concentration
  and salinity
• Radium adsorption with MnOx depends on redox of
  water
• Dissolution
• Low PH and T increase dissolution
• Recoil
• Recoil energy (daughter) following alpha
  disintegration of parent radionuclide
• Change in decay product position in host rock

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Analytical methods
Method 226Ra 228Ra 223Ra 224Ra 222Rn 234U 238U
g spec liquid (1) ? ?
g spec MnO2 (1) ? ? ? ?
RAD 7 MnO2 (2) ?
Delayed coincidence MnO2 (3) ? ?
Emanometry (1) ?
ICP-MS (4) ?
(1) Soreq NRC, (2) BGU University, (3) Stanford
University, (4) NRCN and GSI
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Radiological consequences

• The IL d.w. standard limit the overall dose from
  drinking water to 0.1 mSv/year.
• This limit is translated to activity
  concentration thresholds for each radium isotopes
  as presented in the table.

New IL std Bq/l Old IL std Bq/l Isotope
0.5 0.6 226Ra
0.2 0.5 228Ra
2.1 1.7 224Ra
1.4 223Ra
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Results of method comparison

• Good correlation between different measurement
  methods.

R0.98
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R0.97
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R0.95
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Results of radium mapping

• Radioactivity distribution Dispersion of the
  phenomena along all the study area.
• No hot-spots.
• Anomalies of 222Rn in the region south to the
  Dead Sea.

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Mapping radium conc.
222Rn 224Ra 228Ra 226Ra Name Group
2.5 0.29 0.18 NE Negev - Craters 1
1.8 0.30 0.24 NE Negev Dead Sea 2
3.3 0.44 0.36 South Arava 3
2.5 0.34 0.25 Kurnub Kurnub
6.9 0.08 BDL 0.52 South and central Arava 5
36.5 0.06 BDL 1.52 NE Negev 6
7.4 BDL BDL 0.55 NW Negev 7
14.0 BDL 0.70 Judea Judea
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Study area
Kurnub aquifer
Group 1 NE Negev - Craters
Group 2 NE Negev Dead Sea
Group 3 South Arava
Group 4 Ashalim
Judea aquifer
Group 5 South and central Arava
Group 6 NE Negev
Group 7 NW Negev
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Mapping radium conc.
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Results of drinking water quality

• The majority of the water in both aquifers are
  not suitable for consumption

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Water quality
Kurnub aquifer 66 over old IL std. 96 over new
IL std.
Judea aquifer 34 over old IL std. 38 over new
IL std.
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Results on geochemistry

• Radium isotopes according to lithology (Judea
  226Ra, Kurnub 228Ra and 226Ra).
• Large daughter/parent disequilibrium
• 222Rn/226Ra (0.2 - 225)
• 234U/238U (1.3 - 5.3)
• 224Ra/228Ra (0.1-5.4).

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Lithologic characterization
234U/238U 224Ra/223Ra 228Ra/226Ra Aquifer
3.2 gt30 gt1.5 Kurnub
1.8 lt5 lt0.5 Judea
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Kurnub NE Negev - craters
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Total radium salinity Craters

• High salinity low Ra Adsorption of 226Ra in
  host rock.
• Less precipitation of Ra with BaSO4.

Total radium salinity, DO. NE Negev (DS)
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South and central Arava
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Increase in total Ra with T
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Judea NW Negev
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Ra related to chemistry
Ra release in low DO water
High salinity adsorption sites
Less Ra precipitates with BaSO4
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Conclusions

• A systematic and comprehensive survey of
  natural radioactivity in the Kurnub and Judea
  aquifers was performed.
• The natural radioactivity phenomena in
  groundwater is scattered along the south of
  Israel.
• A comparison of five analytical methods for
  radium measurements was performed and an very
  good correlation was found between the different
  methods.
• Isotopic radium characterization according to
  lithology.
• 228Ra/226Ra lt 1 as expected in carbonate
  aquifers (Judea)
• Almost 40 of the wells do not fit IL and EU
  d.w. Standards.

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• 228Ra/226Ra gt 1 as expected in sandstone
  aquifers (kurnub).
• Almost 96 do not fit new IL d.w. standard
• The groundwater is supplied to the population
  after desalination which lower the radium
  concentration in the water.
• Radium enrichment in groundwater is due to
  adsorption, dissolution, precipitation and
  recoil.
• The predominant geochemical process for radium
  enrichment are influenced in-situ by local
  characteristics (chemistry) of the water.
• High U disequilibrium was found in both
  aquifers.
• High excess of 222Rn was measured in both
  aquifers.

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In cooperation withA. Vengosh and N. Pery Ben
Gurion University.A. Paytan Stanford
UniversitySponsored by Water quality Division
at the Israel Water Commission
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?? ???? ???? 2005
Thank you Gracie ????
Dead Sea