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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]/[]/[

yLqBqSvh

ySvIDClBqGL

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