Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan ...hydrologie.org/redbooks/a232/iahs_232_0081.pdf · 2015. 1. 16. · Natural radioisotopes in groundwaters

Application of Tracers in Arid Zone Hydrology (Proceedings of the Vienna Symposium, August 1994). IAHS Publ. no. 232, 1995. 81

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan: hydrochemical and regulatory implications

R. GEDEON, H. AMRO, J. JAWAWDEH & S. KULANI Laboratories and Water Monitoring Department, Water Authority of Jordan, PO Box 2412, Amman, Jordan

B. SMITH Analytical Geochemistry Group, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

Abstract With expansion in population, increases in industrial activity and the requirement for better health and hygiene, there is an increasing need for high quality water resources. In the semiarid terrains of Africa and the Middle East, the main accessible source of water for potable supply and irrigation is groundwater. Unfortunately, in these regions the majority of deep groundwater resources have appreciable salinity and may only be fit for potable use after mixing with considerable quantities of less saline, shallow groundwaters. This paper describes preliminary studies investigating the vulnerability of groundwater resources in the Amman-Zarka basin of Jordan to contamination by natural series radio nuclides (U, Th, Rn and Ra) from sedimentary phosphate deposits which overlie aquifers within the basin. We present data from (a) an analysis of groundwater samples from pumped boreholes in the Amman-Zarka basin for isotopic (natural series and stable isotopes) and hydrochemical para­meters (major and trace elements, pH, Eh, etc.); and (b) a review of available information relating to the geology, hydrogeology, isotope geo­chemistry (3H, ô180 and ô2H) and hydrochemistry of groundwaters from the Amman-Zarka basin and associated phosphate deposits. Subsequent interpretation of these data indicates that: concentrations of uranium series radioisotopes in groundwaters abstracted from the Amman-Zarka basin for potable supply follow no regional trend; the presence of U series radionuclides shows generally poor correlation with hydrochemical indicators; and there is little evidence of direct contamination from relatively recent phosphate workings. However, localized high concen­trations of radio elements close to the eastern limit of the basin indicate a need for remedial measures to reduce amounts of U, Rn and Ra entering the public supply.

INTRODUCTION

The presence of elevated concentrations of naturally occurring contaminants in ground­water is increasingly being recognized as a limiting factor in guaranteeing the potability

82 R. Gedeon et al.

of water from both shallow and deep groundwater reserves. This is especially true in semiarid regions where high demand, and the scarcity of water, preclude the use of alternative, less contaminated sources.

Whilst potential types and sources of natural contamination are diverse, the scope for contamination of groundwater by naturally occurring radionuclides from the uranium and thorium decay series is potentially high and surprisingly widespread. Systematic studies of waters associated with granitic rocks of Finland (Kahlos & Asikainen, 1980) and sedimentary rocks of Kansas (Spalding & Druliner, 1981) show that the presence of natural radioactivity in drinking water can represent a significant factor in increasing the radiation exposure of the population where the potable supply is obtained from groundwater. More recently, national studies of radionuclide concentrations in water supplies performed in the United States (Longtin, 1988; 1990) have emphasized that, whilst for the majority of the population concentrations of naturally occurring radio­nuclides are well below present or envisaged regulatory guidelines, a relatively large proportion of supplies from aquifers whose host rock is only marginally geochemically enriched in uranium/thorium exceed existing guideline concentrations for radioactivity. This observation implies that the vulnerability of a particular groundwater resource to contamination from naturally occurring radionuclides is not just a simple function of its proximity to mineralization. Rather it is a function of the geochemical, geological and hydrochemical environment in which the groundwater evolves.

Uranium enriched phosphorites of the Late Cretaceous period form an extensive depositional facies throughout North Africa and the Middle East (Wininger, 1954). In Jordan these facies are either exposed, or underlie, approximately 70% of the country's land mass, extending from just north of Amman to Aquaba, and contain between 100 and 200 mg kg"1 of U (Saadi & Shaaban, 1981). Around Amman (Fig. 1) these phos-phatic facies form an integral part of a major, over-exploited aquifer unit within the Amman-Zarka basin, known locally as the B1/2-A7 formation, which contributes approximately 30% of Amman's potable supply. Increased permeabilities in this system along the bed of the Zarka river and Wadi Zarka (UNDP/FAO, 1970) are consistent with a high degree of vulnerability to anthropogenic pollution and natural radioactive compounds leached from thephosphatic wastes, remnants of the now abandoned Rusiefa

JORDAN MIDDLE EAST

Fig. 1 Map showing location of Amman and associated Amman-Zarka basin.

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 83

phosphate mine. This paper describes preliminary studies undertaken:

(a) to investigate the potential vulnerability of groundwater resources in the Amman-Zarka basin of Jordan to contamination by natural series radionuclides (U, Th, Rn and Ra) through an understanding the hydrogeological and hydrochemical charac­teristics of the aquifer and associated geological formations; and

(b) to identify factors controlling water quality in the Amman-Zarka groundwater basin through an assessment of their present day hydrochemistry and the spatial distri­bution of existing natural series isotopes. Whilst the total area of the Amman-Zarka basin is about 850 km2, a preliminary

study area, limited to approximately 250 km2, including Jordan's largest city, Amman, and the Amman-Zarka corridor which links Amman and Zarka via Wadi Zarka and Rusiefa (Fig. 2) was selected for detailed study.

Data collected during initial review and field work, during which groundwater samples were collected from pumped boreholes in the Amman-Zarka basin and analysed for isotopic and hydrochemical parameters, major and trace elements, pH, Eh, etc., are presented in the following sections.

TOPOGRAPHY

Topology and runoff in the area are dominated by the Amman-Zarka synclinal structure, which forms a long depression running southwest to northeast of Amman where it gradually widens. Ground level falls from about 800 to 500 m above sea level along the syncline forming the valley of the river Zarka which leaves the basin at an altitude of 450 m above sea level.

Average rainfall in the area reaches 600 mm per annum on high ground, west of Amman, and decreases rapidly eastwards to reach less than 100 mm per annum east of Zarka.

GEOLOGY AND HYDROGEOLOGY

Formations in the Amman-Zarka basin are predominantly composed of marine sedi­ments deposited during the Lower and Upper Cretaceous periods. The earlier forma­tions, mainly marine carbonates consisting of limestone, sandy limestone, dolomite and marl (Table 1) principally comprise the A1/A2 to A7 formations (Ajlun Group). During the Upper Cretaceous period, depositional changes associated with a marine trans­gression deposited a series of chalks, flints and marls which form the Belqa group formations (Bl/2 to B5).

The Bl/2 and A7 formations together with quaternary soils form the upper aquifer of the groundwater basin. The B1/B2 formation, the lower part of the Belqa group, is locally up to 100 m thick and consists mainly of chalks, limestone cherts and phosphatic beds enriched in U (average 145 mg kg"1, Saadi & Shaaban, 1981). The A7 formation, directly underlies the Bl/2 formation throughout the basin, and consists of white to light gray semi-crystalline limestone which trends towards chalky limestone and marl in basal facies. Typical thicknesses of the A7 in the study area are around 100 m. The lowest

84 R. Gedeon et al.

SCALE = 1:50,000

235 240 245

EASTING

MAJOR ROADS GEOLOGICAL FAULTS

Fig. 2 Map showing location of study area and sampling sites in the immediate vicinity of Amman.

currently exploited aquifer in the basin is formed in the A4 (Hummar) formation which is thought to be relatively confined between the less permeable A3 and A5/6 formations. However, it is equally likely that the A4 formation is relatively unconfined due to the high degree of structural faulting and folding within the Amman area. The A4 formation is light to dark gray limestone, occasionally pinkish, hard grained, dolomitic limestone, is locally between 40 m and 60 m thick and is only exposed at outcrop in the far north of the basin.

Regional groundwater movement within the Amman-Zarka basin is dominated by fracture flow and is predominantly eastwards in accord with the regional dip. Super­imposed upon the general regional flow pattern are a number of influential, localized recharge zones and high ground approximately 3 km west of Amman forms a localized recharge zone for the selected study area. Local recharge in this area results in a westerly flow of groundwater towards the Wadi Sir, an eastward flow of groundwater towards the Azraq basin and a preferred, northeasterly flow of groundwater down the Amman-Zarka syncline to discharge via springs in the upper Zarka valley (UNDP/FAO, 1971). The Amman-Hallabat compressional belt and associated faults (trending parallel to the upper Zarka river; southeast to northeast approx. 5 km south of Amman (Mikbel, 1986)) have maximum displacements of about 300 m and are thought to place the Amman and Wadi Sir formations against the impermeable Muwaqqar formation, thereby forming a barrier to groundwater flow into the Azraq basin and diverting the generally northeasterly flow northwestwards towards Wadi Zarka.

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan

Table 1 Geological formations of the Amman-Zarka basin.

85

Age

Upper Cretaceous

Lower Cretaceous

Epoch

Mastrichian

Campanian

Santonian

Coniacian

Turanian

Cenomanian

Units (Bender-1975)

Chalk-Marl

Phosphorite

Silicified limestone

Massive limestone

Echinoidal limestone

Nodular limestone

Kurnub (Mathira) sandstone

Formations (various)

Muwagger (B3)

Amman (B2)

Rusaifa (Bl)

Wadi Sir (A7)

Shueib

Hummar (A4)

Fuheis

Naour

METHODOLOGY

A total of 27 boreholes and springs were sampled from the Amman-Rusiefa area during February to June 1993. Sampling sites (Fig. 2) were selected to cover as broad a range of supply scenarios as possible, included a number of samples from the deeper A4 aquifer (Table 1) which is also exploited within the basin, and followed a general trend down the hydraulic gradient towards Zarka.

Waters sampled from the well head/spring were preserved according to the protocol shown in Fig. 3. During the sampling process, field measurements (Eh, pH, conduc-

<r HN03 Preserved ICP-OES

ANALYSIS

30 ml

SAMPLE 3~" ?

FIELD TESTS Eh, pH, T, Cond

Alkalinity Rn and Fe(ll)

ISOTOPIC ANALYSIS Ra, »C, 3H

2H and , sO

30 to 100 ml 300 to 25 000 ml

FILTER 0.45 |im

^r r̂ 4 HNO3 Preserved

ICP-MS ANALYSIS

ANION + TOC ANALYSIS

HCI Preserved FIA/AAS

Se Analysis

30 ml 30 ml 30 ml

Fig. 3 Schematic diagram showing sampling protocol used throughout this work.

86 R. Gedeon et al.

tivity, bicarbonate alkalinity and temperature using hand held meters calibrated against standard solutions) were made at the site of collection to avoid degassing of dissolved C02 and significant sorption of atmospheric oxygen. Aliquots of water were also degassed at the well head into "Lucas Cells" to allow the measurement of 222Rn on return to the laboratory. Sub-samples were also collected at this stage for 226Ra analysis by 222Rn emanation.

Major and trace element analysis

Major and trace element determinations were performed on preserved samples after transfer to the British Geological Survey (BGS) laboratory. Major anion and trace element analysis was carried out by inductively coupled plasma optical emission spectro­scopy (ICPOES) using an ARL-3580 simultaneous system. Anion analysis for CI, S04

and N03 was performed with a Dionex 200i ion chromatograph, and HP04 was deter­mined by Flow Injection Analysis (FIA). Total organic carbon and total inorganic carbon were determined with a Shimadzo TOC 5000 analyser standardized against potassium hydrogen phthalate. Analysis for selenium was performed by atomic absorp­tion following hydride generation on filtered acidified samples.

Uranium, thorium and the rare earth elements were quantitatively determined at concentrations between 2000 and 0.1 jxg l"1 by inductively coupled plasma mass spectro­metry (ICPMS), using a VG Plasma quad PQ2 Plus. Semi-quantitative scans between mass numbers 83 and 238 were also performed to confirm the presence of Mo detected by ICPOES, and to investigate the presence of other ultra-trace elements either near or below the detection limit of ICPOES.

The stable isotopes ô180 and ô2H were measured by ratio mass spectrometry; 3H by electrolysis concentration followed by liquid scintillation counting.

Quality assurance of data

Quality assurance of analytical data reported in this work for a wide range of major and trace elements was performed through periodic intercomparison via test waters from the UK-based Aquacheck scheme and through the collection of sample duplicates and blanks during field sampling exercises. Analysis of field blanks and duplicates for both trace and ultra trace elements gave satisfactory results and no indication of airborne contami­nation from dust, filtration media or preservation reagents was observed. Ionic balances on major cations and anions were acceptable with an average charge balance error of —2.5% and an overall range of 0.8 to —6.5%.

The accuracy of U determinations made in this work were verified through the analysis of an international standard basalt (BCR1), as U is not routinely determined within the Aquacheck scheme. For the analysis of Rn and Ra, quality assurance was based on the analysis of an accurately diluted aliquot of a certified 226Ra standard (Certificate No. 425-56-3, Isotope Products Laboratory, Burbank, California, USA).

The accuracy and precision of 3H, 2H and 180 measurements made in this work are verified in the laboratories of the Water Authority of Jordan through participation in IAEA inter comparison exercises and by following IAEA approved protocols.

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 87

RESULTS

Results of chemical analysis for samples are summarized in Tables 2-5 along with results

Table 2 Results of chemical and radiochemical analysis for waters from the Amman-Zarka basin. Sample

JO/93/1 JO/93/2 JO/93/3 JO/93/4 JO/93/5 JO/93/6 JO/93/7 JO/93/8 JO/93/9 JO/93/10 JO/93/11 JO/93/12 JO/93/13 JO/93/14 JO/93/15 JO/93/16 JO/93/17 JO/93/18 JO/93/19 JO/93/20 JO/93/23 JO/93/24 JO/93/37 JO/93/38 JO/93/39 JO/93/40 JO/93/41 JO/93/42 JO/93/43 JO/93/44 JO/93/45

Site No

AL2720 AL1353 AL1360 JO10O0 JO1001 AL1820 AU689 AL1826 AL2368 AL1444 AL1279 AU 843 AL1831 AL2333 AL2334 AU 843 AL2134 AL2114 AL2714 AL1789 AU 643

none AL1811 AL1822 AU836 AL1340 JO1002 JO 1003 AL1830 AL1373 AL1821

Location

Landfill Monitoring Well Shneller School Polytechnique

Rass ain spring New ain Ghazal (station) RuseifaNolO Deep Ruseifa 2a Ruseifa No 17 Ruseifa Sp well no 2 Ruseifa No 8 Ruseifa Municipality no 4 NaserWellNo2 AWSA22RC-22 Race Club No. 29 Race Club No. 17

AWSA33RCN0.2 Race Club No. 34 AL Hazam No. 14 AL Hazam No. 18 AL Hazam No. 12 Wadi Remam

HN03 / Distilled water Blank Maqar Nur Dean Shneller camp Old phosphate mine No. 2 Spring at Ain Ruseifa No. 2 Zarka River Muhajadene No 1 Modem Mill Well Mazara

Area

RUSEIFA RUSEIFA RUSEIFA

AMMAN RUSEIFA RUSEIFA RUSEIFA RUSEIFA RUSEIFA RUSEIFA RUSEIFA AMMAN AMMAN AMMAN AMMAN AMMAN AMMAN AMMAN AMMAN AMMAN AMMAN

na AMMAN AMMAN RUSEIFA RUSEIFA RUSBFA RUSEIFA AMMAN AMMAN AMMAN

Aquifer

B2 B2/A7

A7 1 ?

B2/A7 A4 A4 ?

B2/A7 B2/A7 B2/A7 B2/A7

? B2/A7/A4 ?

B2/A7 ? ? ?

B2/A7 ? K7B2/A7

na B2/A7/A4 B2/A7/A4

A4 B2/A7 ?

? na

B2/A7 A4 A4

Temp

•c 20.3 22.5 22.6 18.7 20.9 22.0 26.0 22.7 20.8 20.7 22.6 20,5 21.7 27.9 22.1 20.4 22.5 21.5 22.9 23.2 21 na

23.1 23.6 26.5 22.4 19.7 21.7 20.5 21.2 22.8

pH

6.88 7.03 7.30 6.72 6.84 7.08 7.42 7.42 7.27 7.25 7.38 7.25 7.07 7.64 7.20 7.15 7.20 7.15 7.48 7.97 7.08 na

7.19 7.10 7.30 7.23 7.22 7.46 7.13 7.06 7.55

Eh mV

441.7 561.5 482.4 937.3 582.1 487.0 465.0 471.3 463.2 459.3 472.4 433.5 372.3 -3.9

294.9 314.6 316.5 322.5 322.1 321.8 367.0

na 755.9 449.4 849.5 681.6 541.3 553.3 861.5 705.8 297.2

Cond US

1392 1010 850 602 1170 878 558 750 670 760 640 835 880 1450 780 880 660 740 608 600 1000 na

1110 1090 677 860 720 680 820 940 580

Bicarb ppm 352 293 281 243 369 353 289 344 287 331 294 315 340 254 299 362 299 340 276 298 377 na

347 352 326 321 298 304 304 304 304

Ca ppm

110 100

88.2 81.1 134

94.6 50.6 93.7 94.2 97.3 72.8 109 116

67.3 95.4 113

86.5 103

71.4 57.0 120

0.030 104 104

63.8 97.5 94.1 90.8 114 117

49.1

Mg ppm

30.6 29.9 21.9 12.2 24.6 27.2 30.8 28.3 21.0 24.3 28.0 20.9 21.9 31.2 25.6 22.3 26.2 22.5 21.2 29.3 24.5

<0.030 34.0 34.5 34.4 23.3 20.9 21.8 16.0 22.7 30.6

Na ppm

114 65.1 60.1

17.9 77.8 66.6 16.3 57.0 45.3 91.4 59.8 51.0 58.6 206

43.1 53.7 47.1 48.0 43.9 33.4 57.0

0.035 58.3 58.3 30.1 65.5 44.6 50.4 46.3 65.4

26.6

K ppm

5.88 3.52 3.71

1.25 9.19 6.25 2.25 4.69 3.71 5.62 4.55 6.66 7.28 1.21 2.71 6.15 2.61 4.58 2.86 3.06 7.31

<0.100 6.73 6.63 2,51 5.08 3.98 4.73 4.62 11.8 1.50

CI ppm

224 119 122

46 155 119 26

101 87

152 104 114 128 330

98 119 103 108 90 58

124

<2 121 120 57

123 88 97 99

130 46

na - not determined

Table 3 Results of chemical and radiochemical analysis for waters from the Amman-Zarka basin.

Sample

JO/93/1 JO/93/2 JO/93/3 JO/93/4 JO/93/5 JO/93/6 JO/93/7 JO/93/8 JO/93/9 JO/93/10 JO/93/11 JO/93/12 JO/93/13 JO/93/14 JO/93/15 JO/93/16 JO/93/17 JO/93/18 JO/93/19 JO/93/20 JO/93/23 JO/93/24

JO/93/37 JO/93/38 JO/93/39 JO/93/40 JO/93/41 JO/93/42

JO/93/43 JO/93/44

JO/93/45

Site No

AL2720 AL1353 AL1360

JO1000 JO1001 AL1820 AL1689 AL1826 AL2368 AL1444 AL1279 AL1843 AL1831 AL2333 AL2334 AL1843 AL2134 AL2114 AL2714 AL1789 AL1643

none AL1811 AL1822 AL1836 AL1340 JO1002 JO1003 AL1830 AL1373 AL1821

Location

Landfill Monitoring Well Shneller School Polytechnique Rass ain spring New ain Ghazal (station) RuseifaNolO Deep Ruseifa 2a Ruseifa No 17 Ruseifa Sp well no 2 Ruseifa No 8 Ruseifa Municipality no 4 NaserWellNo2 AWSA22RC-22 Race Club No. 29 Race Club No. 17 AWSA 33 RC No. 2 Race Club No. 34 AL Hazam No. 14 AL Hazam No. 18 AL Hazam No. 12 Wadi Remam

HN03 / Distilled water Blank Maqar Nur Dean Shneller camp Old phosphate mine No. 2 Spring at Ain Ruseifa No. 2 Zarka River Muhajadene No 1 Modem Mill Well Mazara

Sulphate ppm

33.4 33.1 27.8 13.0 29.4 43.8 24.1 35.7 28.2 35.4 35.5 15.1 14.8 97.1 19.5 15.6 21.0 16.7 23.9 43.2 16.7

<2 49.0 49.2 34.4 34.3 27.5 29.3 14.5 27.1 31.9

Nitrate ppm (N03)

61.8 74.7 46.7 37.8

112.0 27.0

1.4 43.0 53.2 49.7 36.8 78.9 89.9 <20 68.0 84.8 54.8 61.1 27.5 11.5 95.4 0.1

67.0 65.9

8.1 54.9 54.0 40.0 93.7 90.8 4.3

Br ppm

0.8 0.4 0.5

<0.05 0.4 0.4 0.1 0.4 0.3 0.5 na na na na na na na na

0.4 0.3 0.4

<0.05 na

0.4 <0.1 0.5 0.3 0.4

<0.1 0.4

<0.1

TOC ppm <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00 <1.00

1.68 <1.00 <1.00 <1.00

1.10

<i.oo <1.00

2.05 2.13

<1.00 <1.00 <1.00

Phosphate FIA ppm

<0.05 <0.05 <0.05 <0.05 <0.05

0.18 <0.05

0.12 0.11 0.06

<0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

0.12 0.61

<0.05 <0.05 <0.05

Sr ppm 0.540 0.636 0.425 0.246 0.530 0.434 0.614 0.434 0.417 0.470 0.477 0.431 0.449 0.672 0.499 0.464 0.449 0.441 0.417 0.532 0.502

<0.002 0.501 0.521 0.541 0.458 0.417 0.427 0.415 0.465 0.448

Ba ppm 0.129 0.129 0.124 0.104 0.161 0.134 0.181 0.154 0.086 0.091 0.111 0.182 0.159 0.188 0.188 0.169 0.155 0.142 0.121 0.105 0.159

<0.002 0.146 0.180 0.180 0.107 0.085 0.085 0.190 0.155 0.109

B ppm 0.235 0.208 0.131 0.035 0.139 0.209 0.036 0.171 0.120 0.199 0.119 0.097 0.112 0.433 0.100 0.100 0.100 0.099 0.092 0.095 0.135

<0.020 0.130 0.130 0.078 0.181 0.124 0.125 0.097 0.142 0.068

Si ppm

6.87 6.87 6.39 6.52 7.24 7.12 6.44 7.40 7.33 6.84 7.33 6.58 6.64 2.78 6.41 6.35 6.31 6.36 6.23 6.58 6.94

<0.020 6.85 7.03 7.15 6.75 7.30 5.21 6.62 7.22 6.70

Mn ppm <0.01 <0.01 <0.01 •cO.01 <0.01 0.008 0.005 0.006 0.009 <0.01 <0.01 <0.01 <0.01 0.654 <0.01 <0.01 0.006 <0.01 <0.01 0.008 <O.01 <0.01 0.030 0.046 <0.01 <0.01 <0.01 0.015 <0.01 0.008 <0.01

Fe ppm

<0.010 0.029

<0.010 <0.010 <0.010

0.015 0.035 0.012

<0.010 <0.010 <0.010

0.044 <0.010

5.29 0.016

<0.010 0.017

<0.010 <0.010 <0.010 <0.010 <0.010

0.018 0.034

<0.010 0.031

<0.010 0.028

<0.010 0.039 0.086

na = not determined

88 R. Gedeon et al.

Table 4 Results of chemical and radiochemical analysis for waters from the Amman-Zarka basin.

Sample

JO/93/1 JO/93/2 JO/93/3 JO/93/4 JO/93/5 JO/93/6 JO/93/7 JO/93/8 JO/93/9 JO/93/10 JO/93/11 JO/93/12 JO/93/13 JO/93/14 JO/93/15 JO/93/16 JO/93/17 JO/93/18 JO/93/19 JO/93/20 JO/93/23 JO/93/24 JO/93/37 JÔ/93/38 JO/93/39 JO/93/40 JO/93/41 JO/93/42 JO/93/43 JO/93/44 JO/93/45

Site No

AL2720 AL1353 AL1360 JO1000 JO1001 AL1820 AL1689 AL1826 AL2368 AL1444 AL1279 AL1843 AL1831 AL2333 AL2334 AL1843 AL2134 AL2114 AL2714 AL1789 AL1643

none AL18U AL1822 AL1836 AL1340 JO1002 JO1003 AL1830 AL1373 AL1821

Location

Landfill Monitoring Well Shneller School Polytechnique Rassain spring New ain Ghazal (station) RuseifaNolO Deep Ruseifa 2a Ruseifa No 17 Ruseifa Sp well no 2 Ruseifa No 8 Ruseifa Municipality no 4 NaserWeUNo2 AWSA22RC-22 Race Club No. 29 Race Club No. 17 AWSA 33 RC No. 2 Race Club No. 34 ALHazamNo. 14 ALHazamNo. 18 AL Hazam No. 12 Wadi Remain HN03 / Distilled water Blank Maqar NurDean Shneller camp Old phosphate mine No. 2 Spring at Ain Ruseifa No. 2 Zarica River Muhajadene No 1 Modem Mill Well Mazara

Fell ppm <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

0.01 <0.01 <0.01 <0.01 <0.01

0.01 <0.01

6.34 0.01

<0.01 0.03 0.01 0.01

<0.01 <0.01

0.01 0.11 0.03 0.05

<0.01 0.02 0.03

<0.01 0.07

Li ppb

<3 3.56 3.07

<3 <3 <3

3.38 <3 <3

4.36 <3 <3 <3

9.01 <3 <3 <3 <3

3.17 3.04

<3 <3

3.33 3.00 3.90

<3 <3

3.19 <3 <3

3.16

Be ppb <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5

Al ppb <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 33.1 <30 <30 <30 <30 <30 <30 <30 <30

V ppb

<5 18.6 17.2

<5 10.9 5.29

<5 6.03 9.29 8.82 8.48 9.03 8.06 7.41 12.8 10.6 14.2 13.8 37.1 103

5.14 <5

16.7 11.1 6.33 9.29 U.4 13.3 11.1

<5 58.9

Cr ppb <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 10.5 <10 <10 <10 <10 <10 <10 <10 <10

Co ppb

<10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10

Ni PPb

<10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 22.6 <10 <10 38.0 26.3 <10 <10 <10 <10 <10 <10 12.2

Cu ppb

•a <7 <7 <7 <7 <7 <7 <7 <7 <7 <7 <l

•a <7 <7 <7 •a <l <7

21.7 <7

20.3 <7 <7

8.80 <1 <7 <7

8.20 •a <7

Zn PPb

415 18.3 18.2 120 17.3

<5 11.6

<5 <5 <5

80.3 74.8 83.3 7.47 24.2 28.4 21.5 34.1 21.4 37.3 15.0 5.98 26.6 47.3

<5 <5 <5 <5

347 13.8 13.7

Zr ppb

<5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5

Mo ppb

<10 <10 11.8 <10 <10 18.8 15.8 <10 <10 17.1 <10 12.5 11.3 15.2 <10 14.9 <10 17.3 71.3 153 <10 <10 629 608 54.8 <10 14.7 <10 10.7 <10 171

Cd ppb

<5 <i <5 <5 <i <5 <5 <i <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <•>

<5 <5 <5

Pb ppb <30 <30 <30 <30 <30 <30 <30 <30 <30 <J0 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <10 <30 <30 <30

na - not determined

Table 5 Results of chemical and radiochemical analysis for waters from the Amman-Zarka basin.

Sample

JO/93/1 JO/93/2 JO/93/3 JO/93/4 JO/93/5 JO/93/6 JO/93/7 JO/93/8 JO/93/9 JO/93/10 JO/93/11 JO/93/12 JO/93/13 JO/93/14 JO/93/15 JO/93/16 JO/93/17 JO/93/18 JO/93/19 JO/93/20 JO/93/23 JO/93/24 JO/93/37 JO/93/38 JO/93/39 JO/93/40 JO/93/41 JO/93/42 JO/93/43 JO/93/44 JO/93/45

Site No

AL2720 AL1353 AL1360 JO1000 JO1001 AL1820 AL1689 AL1826 AL2368 AL1444 AL1279 AL1843 AL1831 AL2333 AL2334 AL1843 AL2134 AL2114 AL2714 AL1789 AU 643

none AL1811 AL1822 AL1836 AL1340 JO1002 JO1003 AL1830 AL1373 AL1821

Location

Landfill Monitoring Well Shneller School Polytechnique Rass ain spring New ain Ghazal (station) Ruseifa No 10 Deep Ruseifa 2a Ruseifa No 17 Ruseifa Sp well no 2 Ruseifa No 8 Ruseifa Municipality no 4 NaserWellNo2 AWSA22RC-22 Race Club No. 29 Race Club No. 17 AWSA 33 RC No. 2 Race Club No. 34 AL Hazam No. 14 AL Hazam No. 18 AL Hazam No. 12 Wadi Remain HN03 / Distilled water Blank Maqar NurDean Shneller camp Old phosphate mine No. 2 Spring at Ain Ruseifa No. 2 Zarka River Muhajadene No 1 Modem Mill Well Mazara

Total REE ppb <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Th PPb 0.16 0.03 0.02 0.04 0.02 0.05 0.11 0.03 0.03 0.01 0.03 0.01 0.13 0.01 0.04 0.02 0.01 0.00 0.17 0.04 0.01 0.02 0.00 0.01 0.04 0.01 0.01 0.00 0.01 0.00 0.08

U ppb 1.89 3.43 2.21 1.25 2.78 10.49 24.58 2.60 1.97 2.33 1.80 1.98 2.00 -0.01 2.09 2.04 1.92 1.93 5.65 9.88 2.18 0.06

1186.63 1145.10

4.92 2.23 2.23 2.34 2.23 2.41 25.04

Ra pCi/1

4.20

4.91

10.00

4.60 12.60

4.60 6.00 5.30

7.72

151.00 84.00

4.80 5.30

Rn pCi/1 895 291 849 853

4293 649 1358 453 1148 3226 1808 2738 4338 930 5065 1773 3324 1099 1053 na

5139 na

19305 21839 2145 3387 1446 na

3012 2159 1334

Se ppb 1.46 0.75 6.43 0.44 2.04 60.46 17.86 0.88 0.55 0.09 38.84 2.71 3.06 -0.31 12.75 3.7 20.7 5.63

30.55 170.21

na na

10.19 75.82

na na na na na na 45

Tritium TU 4.1 na 3.8 8.2 4

2.7 5

0.9 0.9 na 4.9 3.7 3.6 na 4.3 na 1.8 1.5 na na 3.8 na 3.3 0

0.2 6 na na 5.3 2.1 0

Delta 0-18 per mil -5.59

na -5.6 -6.2 -5.64

-6 -6.27

-6 -5.41

na -5.43 -5.59 -5.64

na -5.6 na

-5.67 -5.4 na na

-5.97 na

-6.04 -6.38 -6.18 -5.37

na na

-5.78 -6.03 -6.17

Delta D per mil

-27 na

-26.6 -27.4 -27.5 -27.8 -29.4 -29.3 -27 na

-26.9 -26.8 -27 na

-26.7 na

-26.6 -27.3

na na -28 na

-27.7 -28.7 -30.4 -26.3

na na -27

-28.1 -29.4

na = not determined

of environmental stable (2H, 180) and radioactive isotopes including 3H. Figure 2 shows the spatial distribution of sampled sites along with the borehole identification numbers and topographic features such as roads, urban areas and major geological faults.

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 89

Results from the analysis of a distilled water/Analar HN03 blank (JO/93/24) are at or acceptably near detection limits for respective methodologies, except in the case of Cu where a concentration of 20 /xg l"1 was determined. The origin of this relatively high Cu blank cannot be due to the sample preservation procedure (i.e. the presence of Cu in the nitric acid) as it is not observed in the majority of samples which show levels lower than the detection limit (7 /ig l"1), and can only be attributable to random noise for, or contamination of, that particular determination. Duplicate determinations of the Maqar sample (JO/93/21 and JO/93/22, not shown in this table) agreed to better than 10% except in cases where the concentration was close to the methods detection limit.

DISCUSSION

Groundwater samples described above were collected from boreholes at the well head, and as most wells sample from at least two aquifer units (the B1/B2 and A7) mixing between waters must occur during pumping prior to sample abstraction. The attribution of samples to particular aquifer units to define hydrochemical characteristics of aquifer units was also found to be difficult because of the lack, and in some cases the contra­dictory nature, of borehole records. In the following discussions it is therefore difficult to attribute water chemistry to any particular aquifer on the basis of well depth, other than to give a broad indication on the basis of existing records.

Major elements, Eh and pH

Data for determination of major elements are displayed in Fig. 4 via a Piper diagram. From this it can be seen that the majority of samples are broadly similar with respect to both their cation and anion chemistries, being Ca and bicarbonate dominated with minor contributions from Mg, Na, CI and S04. Nitrate is generally high in the majority of wells within the B2/A7 system and is evidence of considerable anthropogenic contamina­tion. A number of obvious exceptions do however exist: (a) Samples from AL1689, AL1823, AL1821, AL1836 and AL1789 form a grouping

with a higher prevalence of Mg, with a Mg:Ca ratio close to 1 indicative of equili­brium with dolomite, the same samples are also less influenced by chloride which may indicate less anthropogenic pollution as these waters are also low in nitrate. Records show these wells to be A4, A4, A4, A4 and B2/A7 respectively, although a number of other wells identified as intercepting the A4 formation plot within the main grouping, possible due to a higher anthropogenic component such as Na. These same waters have a generally lower tritium content and are more depleted in 180 and 3H than the main data grouping.

(b) Sample JO1000, directly recharged water from a major spring in central Amman, which dries up in summer.

(c) AL1380, a shallow, B2/A7, well in central Amman, grossly contaminated with nitrate (approx. 100 mg l"1).

(d) AL2333, an apparently deep reducing well in the south of Amman, possibly influenced by thermal waters (temperature 28°C, low Eh, high Li) and close to known deep faulting associated with the Amman-Hallabat structure.

R. Gedeon et al.

CATIONS ANIONS

Fig. 4 Piper diagram showing major element chemistry of waters sampled from the Amman-Zarka basin.

(e) AL2720, a landfill monitoring well, likely to be enhanced in CI, bicarbonate and nitrate due to leakage of leachate. The pH and Eh of the sampled waters (Fig. 5) are generally characteristic of rela­

tively juvenile, karstic waters with pH being between 7 and 8 and Eh above 200 mV. The exception to this was AL2333 which was markedly more reducing (Eh < 0 mV) and contained both Fe (II) and significant Mn. The range of Eh and pH observed in all of the sampled waters with exception of AL2333 (Racing Club 29), along with the domi­nance of bicarbonate suggests that speciation of redox sensitive elements would favour carbonate complexes of the oxidized cation. In the case of U this would enhance its mobility and general solubility.

Trace elements, uranium, radium and radon

The rare earth elements are present at concentrations below their detection limit (1 fig l"1) in all cases, as are concentrations of HP04 (colorimetrically determined by FIA), Be, Al, Co, Th and Y. The majority of waters are also low in TOC and Li. Uranium was determined to be above detection limit in all but one sample (Racing Club 29) from this region. The absence of dissolved U in this particular water can be attributed to its low Eh which would reduce relatively mobile U(VI) to immobile U(IV) (Fig. 5).

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 91

Fig. 5 Eh-pH diagram showing distribution of measurements superimposed on stability fields for U and Fe in an U-C-O-H and Fe-S-O system (adapted from Brookins, 1988).

Average U, Rn and Ra concentrations are 164 ^g r1, 4942 pCi l"1 and 22 pCi l"1, respectively. However, on closer examination of the data it is clear that average concen­trations are strongly biased by the high concentrations in samples AL1811 and AL1822 (Maqar and Nur Dean). The overall spatial distribution of U and Rn are displayed in Figs 6 and 7 respectively. Concentrations of U in waters from AL1811 and AL1822 are over two orders of magnitude greater than from others in the sample set and also show enhanced concentrations of other trace metals (Ni, Zn, Mo and V) compared to other wells in this data set.

The occurrence of Se and Mo at concentrations exceeding 20 fig Ï1 in the majority of these waters is especially noteworthy as is the apparent correlation between the high concentrations of Mo and U. Semi-quantitative ICPMS scans of samples from Maqar and Nur Dean also revealed the presence of rhenium (approximately 5 /ug l"1) and thallium (approximately 1 jug l"1). Such occurrences in groundwater are generally rare, although U, Mo, Re and V may be associated in oxidizing groundwaters in regions of extensive U mineralization. Ba and Sr concentrations are relatively high in all sampled waters, a factor which would be consistent with high Ra mobility.

Apart from the high trace element contents observed in a relatively large number of wells within the region of the Amman-Zarka basin sampled in this study there are no distinct hydrochemical or isotopic indicators that indicate extremely high U contents observed in samples from AL1811 and AL1822 form part of a regional trend. Further­more similar concentrations are not seen elsewhere in waters sampled from either the B1/B2, A7 and A4 formations indicating a point source (i.e. secondary U mineraliza­tion) rather than a diffuse source from, for example, the surficial U rich phosphates. The presence of elevated concentrations of other, rare, trace elements such as Mo which are

92 R. Gedeon et al.

commonly associated with U in redox controlled mineralization (i.e. roll front type mineralization) would also be consistent with the former.

IE SCALE (ug/1)

® @ 0 500 1000

i N i i i i i i

EASTING AMMAN-ZERQA SCALE = 1:50 000

Fig. 6 Proportional symbol map showing distribution of uranium. (Note: all sampling sites in Fig. 2 sampled.)

-

-

\ SCALE (pCi/l)

0 5 000 10 000

\ \

~ \ . \\

- \

1W7 ~\s\£ 1 / i l l A 1

ÏC

<<\

/ / /

i i i i i

-^W

i i i

EASTING AMMAN-ZERQA SCALE = 1:50 000

Fig. 7 Proportional symbol map showing distribution of radon. (Note: all sampling sites in Fig. 2 sampled.)

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan

Stable isotopes and tritium

93

Data for stable isotopes (Fig. 8(a)) indicate that waters of all three major aquifer units within the Amman-Zarka basin (B1/B2, A7 and A4) are of Mediterranean origin and have a similar deuterium excess of approximately 20 to 25 %>.

Whilst data is relatively tightly grouped within the range —5 to — 6%o for ô180 and

0

S -100

Q

-200

-300

: (a)

;

^ "

1 1 1 1

Slope = Deuterium

to'cariviwc 8.17 De l ta 1 ^ Excess 20 to :

• • • i

23.2 5 o/oo

1 1 i n 1

• 1 1 1 ' 1 1 ' ! —F

':

;

;

:

'•

-30

-15

-20

— -25 Q

-30

-35

-25 -20 -15 -10

<51 80 (%o)

-6.5 -6 -5.5 <51 S0 (%o)

-4.5

Fig. 8 (a) Plot of S180 vs ô2H showing the relationship between measured values and the local meteoric water line (MWL); (b) expanded plot of SlsO vs d2H showing the relationship between measured values, the local meteoric water line (MWL) and evaporation/mixing lines.

94 R. Gedeon et al.

-32 to -26%o for <52H, closer examination of the data (Fig 8(b)) shows a linear trend away from the local meteoric water line (MWL) with a slope of ô2H = 3.4 <5180 - 7.9. The slope of this observed trend is slightly lower than would be expected from a typical evaporation line (slope = 5) and would therefore be consistent with a combination of evaporation and/or mixing between waters of different isotopic enrichment. ô180 was plotted against CI concentration (Fig. 9) to establish any correlation that could be attri­butable to evaporation. Three distinct groups of data (A, B, C) can be observed and suggest that the correlation observed in Fig. 8(b) is consistent with a combination of mixing between end members, low in CI and depleted with respect to both 2H and 180 in one case and relatively high CI waters enriched in both 2H and 180 in the other, and evaporation. On further investigation a similar through less clear trend was observed between <5180, N03 and 3H.

Tritium contents of waters sampled in this work range between 0 and 8 tritium units, which corresponds to the tritium concentration of present-day precipitation over Amman. Generally poor correlations are observed between the 3H content of samples and other indicators of recent, anthropogenically polluted waters, such as N03 and CI. This is consistent with mixing between waters from different aquifers during sampling and is not observed in boreholes which are exclusively screened over single formations such as the A4 (sites, AL1823 and AL1821).

Implications to health and water quality

Existing WHO guideline values (WHO, 1984a; 1984b) of 1.0 Bq 1"l for gross beta acti­vity and 0.1 Bq l*1 for gross alpha activity take into account both naturally-occurring radioactivity and radioactivity that may reach water sources as a result of man's acti­vities. It should be noted that the guideline value for gross alpha activity excludes any contributions from radon which should be degassed prior to measurement.

In the case of U there has been no direct epidemiological study of the radiochemical toxicity of uranium. However, it is known that between 1 and 5 percent of ingested uranium migrates to bone and deposits in a similar way to radium (Cothern, 1987). If it is assumed that dissolved uranium in groundwater is not in radioactive equilibrium with its daughters then 1 fig l"1 U would have an activity of 0.025 Bq l"1. On this basis the WHO radiochemical guideline value for gross alpha activity would be exceeded at a concentration of 4.0 /ig l"1. Alternatively, if U was in equilibrium with daughters down to radium, then the WHO guideline value would be reached at approximately 1.3 fig l"1.

More detailed calculations following IAEA (1989), which take into account the uptake of U, show that rigid adherence to the WHO guideline value of 0.1 Bq l"1 over­estimates the radiological toxicity. However, in addition to its radiochemical toxicity, uranium is also chemically toxic to the kidneys. Wrenn et al. (1985) give evidence from medical administration to humans and animals. Nephritis (inflammation of the kidneys) and changes in urine consumption are cited as clear symptoms. On the basis of chemical toxicity these authors quote an acceptable intake of uranium from potable water to be 60 fxg l"1, computed by allocating the total acceptable daily intake for a 70 kg adult to the consumption of 2 1 of water per day. This is equivalent to 0.75 Bq l"1 or 20 pCi l"1

for natural U, only, and a dose of 88 /uSv per year based on a committed dose equivalent factor of 2 x 10"9 Sv fig1 and a transfer factor of 0.05 (IAEA, 1989).

On the basis of the above evidence and analytical data it is clear that groundwater

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 95

-5.2

-5.4

-5.6

O -5.8 CO

"H5

-6.2

-6.4 50 200 100 150

CI concentration (mg I"1)

Fig. 9 Plot of CI concentration vs ô180 showing the tree group described in the text.

250

from Maqar and Nur Dean greatly exceed even the conservative guideline values described above. The rest of the sampled sites generally show U concentrations below 20 ixg l"1 and as such do not present a significant risk.

WHO guidelines for Rn have not been set, and it is only possible to apply a similar rationale to that for U and use a concentration of radon that would give a committed annual dose equivalent from water of 50 pSv in a year. This equates to a concentration of 4.63 Bq l"1 (125 pCi l"1), assuming a committed effective dose equivalent factor for ingestion of 222Rn in water of 1.46 x 10"8 Sv per Bq (Kendall, 1988) and the ingestion of 2 1 of water a day. However, the majority of tap water ingested each day in Jordan is consumed as hot drinks, such as tea or coffee, in which all Rn is likely to have been lost. A more appropriate value for the consumption of "un-prepared" tap water might be 0.11 per day , in which case a committed dose of 50 /itSv would equate to a concen­tration of 92.5 Bq l"1 (2500 pCi l"1). On this basis the guideline value for ingestion of Rn might therefore be set at around 2500 pCi l"1 (approximately 100 Bq l"1). If such a tenta­tive guideline value of 2500 pCi l"1 is assumed for potable waters in Jordan, WAJ data collected from a preliminary survey of wells in 1992/1993 and data from this exercise indicate that about 25 to 30% of wells when sampled at source exceed this value. Again, Maqar and Nur Dean exceed this guideline value by up to a factor of 10.

At low and medium doses radium is deposited in bone and the most severe biological damage is cancer arising in skeletal tissue. For 226Ra two types of malignancy are induced: bone sarcoma and head carcinoma. Extensive studies of radium workers who were exposed to relatively high doses through ingestion has resulted in a high degree of confidence in the toxicological data relating to radium (both 226Ra and 228Ra). Typical average intakes for ingestion, through drinking water, in the USA have been estimated to be between 0.022 and 0.074 Bq day"1 Cothern (1987). Based on ingestion of 2 1 of

96 R. Gedeon et al.

water a day this results in a dissolved concentration of less than 0.037 Bq l"1 (1 pCi l"1). Removal of radium from solution during the preparation of tea or coffee would be expected to be more limited than for radon, and the adoption of an intake of 2 1 of tap water a day is more appropriate in this case.

WHO do not give a separate guideline value for radium in potable water. The US EPA give a maximum permissible concentration of 226Ra and 228Ra combined as 0.185 Bql"1 (SpCiT1), whilst the Canadian maximum acceptable limit (MAL) is 1 Bq l"1

(27 pCi l"1). On the basis of 226Ra which is estimated to be far more common than 228Ra in environments enriched in uranium rather than thorium a concentration of 0.185 Bq l"1

(5 pCi l"1) equates to a committed annual dose of 43 /iSv (using data from IAEA, 1989). Data from this survey indicates that a significant proportion of well waters exceed this concentration. However as more than 90% of the wells have concentrations less than 1 Bq T1 (27 pCi l"1, the Canadian MAL) there is less general cause for concern.

CONCLUSIONS

Results indicate that groundwaters in the Amman-Zarka basin show little differentiation in terms of major element chemistry, being predominantly near neutral, oxidizing Ca/Mg/bicarbonate waters. The major exception to this general observation is water from well Race Club 29 (AL2333) which is markedly more reducing and saline than other waters. This, together with its elevated temperature, may indicate that water from this well originates from a deeper groundwater source whose upward transport is influenced by deep seated faulting within the Amman-Hallabat structure.

The trace element chemistry generally shows more spatial variation. At least three groundwater sources show markedly elevated concentrations of U, Rn, Mo, V and Se. The highest concentrations of U, Rn and Mo were detected in waters from Maqar and Nur Dean (AL1811 and AL1822). Water from the Modern Mill (AL1373) well although spatially close to Maqar and Nur Dean clearly abstracts water from a different source because high concentrations of U, Mo etc. are not evident.

The similarity in major element hydrochemistry and the high spatially variability of trace element data indicate that a point source rather than diffuse source is responsible for the enhanced radio element content of AL1811 and AL1822. This indicates that it is unlikely that dissolution of U rich phosphate is a contributing factor in these particular wells. The low regional concentrations of U and Rn observed to date suggest the phosphate is unlikely to release significant quantities of the radionuclides into the Amman-Zarka basin as a whole.

Localized high concentrations of radio elements in AL1811 and AL1822 close to the eastern limit of the basin indicate a need for remedial measures to reduce amounts of U, Rn and Ra entering public supply from these two wells. However, further more detailed investigations are required to identify the source term of this contamination and to identify if other wells down hydraulic gradient are at risk.

Acknowledgements The authors would like to acknowledge support from the IAEA through contract JOR/9/004-01, and from the United Kingdom Overseas Development Administration without which this work would not have been possible.

Natural radioisotopes in groundwaters from the Amman-Zarka basin, Jordan 97

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