Natural radioactivity in groundwater in the Negev Desert and the Arava Valley, Israel
Gustavo Haquin Soreq Nuclear Research Center, Yavne 81800ISRAEL
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
Natural decay series
DeadSea
Cyprus
Red Sea
Arava valley
Negev Desert
SinaiPeninsula
Study area
Group 1: NE Negev - Craters
Group 7 : NW Negev
Group 6: NE Negev
Group 5: South and central Arava
Group 4: Ashalim
Group 3: South Arava
Group 2: NE Negev – Dead Sea
Kurnub aquifer
Judea aquifer
Precipitation Enrichment of SrSO4 and PbSO4 instead of BaSO4 – atomic
radius Decrease in radium content in solid with increasing
temperatureAdsorption 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 waterDissolution Low PH and T increase dissolutionRecoil Recoil energy (daughter) following alpha disintegration of parent radionuclide Change in decay product position in host rock
Processes for radium enrichment in ground water
Analytical methods
Method 226Ra 228Ra 223Ra 224Ra 222Rn 234U238U
spec – liquid (1)
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
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.
Isotope Old IL std[Bq/l]
New IL std [Bq/l]
226Ra 0.6 0.5
228Ra 0.5 0.2
224Ra 1.7 2.1
223Ra 1.4
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ing
12
2
1
1 n
n
X
C
X
C
X
C
Results of method comparison Good correlation between different
measurement methods.
0.00 0.25 0.50 0.75 1.00 1.25 1.500.00
0.25
0.50
0.75
1.00
1.25
1.50
Mn
O [B
q/l]
RAD 7 [Bq/l]
Comparison: 226RAD 7 - MnO
R=0.98
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
R
AD
7 [B
q/l]
spec [Bq/l]
Comparison: 226 spec - RAD7
R=0.97
0.0 0.2 0.4 0.6 0.8 1.00.0
0.2
0.4
0.6
0.8
1.0
M
nO [B
q/l]
spec [Bq/l]
Comparison: 228 spec - MnO
R=0.95
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.
Mapping radium conc. Group Name 226Ra 228Ra 224Ra 222Rn
1 NE Negev - Craters
0.18 0.29 2.5
2 NE Negev – Dead Sea
0.24 0.30 1.8
3 South Arava 0.36 0.44 3.3
Kurnub 0.25 0.34 2.5
5 South and central Arava
0.52 BDL 0.08 6.9
6 NE Negev 1.52 BDL 0.06 36.5
7 NW Negev 0.55 BDL BDL 7.4
Judea 0.70 BDL 14.0
Study area
Group 1: NE Negev - Craters
Group 7 : NW Negev
Group 6: NE Negev
Group 5: South and central Arava
Group 4: Ashalim
Group 3: South Arava
Group 2: NE Negev – Dead Sea
Kurnub aquifer
Judea aquifer
Mapping radium conc.
Results of drinking water quality
The majority of the water in both aquifers are not suitable for consumption
Kurnub aquifer66% over old IL std.96% over new IL std.
Judea aquifer34% over old IL std.38% over new IL std.
Water quality
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).
Kurnub
Judea
Lithologic characterization
Aquifer 228Ra/226Ra 224Ra/223Ra 234U/238U
Kurnub >1.5 >30 3.2
Judea <0.5 <5 1.8
KurnubNE Negev - craters
Total radium – salinityTotal radium – salinityCratersCraters
Total radium – salinity, DO. NE Negev (DS)Total radium – salinity, DO. NE Negev (DS)
High salinity – low Ra: Adsorption of 226Ra in host rock.
Less precipitation of Ra with BaSO4.
South and central Arava
Increase in total Ra with T
כורנוב
יהודה
JudeaNW Negev
Low salinity300 mg/L
High salinity1500 mg/L
Ra release in low DO waterHigh salinity –
adsorption sitesLess Ra precipitateswith BaSO4
Ra related to chemistryRa related to chemistry
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 < 1 as expected in carbonate aquifers (Judea)
Almost 40% of the wells do not fit IL and EU d.w. Standards.
228Ra/226Ra > 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.
In cooperation with
A. Vengosh and N. Pery – Ben Gurion University.
A. Paytan – Stanford University
Sponsored by: Water quality Division at the
Israel Water Commission
Thank youGracieתודה
Dead Sea