gw degradation in the northeastern part of mafraq.pdf

7/29/2019 GW degradation in the northeastern part of Mafraq.pdf

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Freshwater Contamination (Proceedings of Rabat Symposium S4, April-May 1997).IAHS Publ. no. 243, 1997 235

Groundwater degradation in the northeastern partof M afraq area, Jord an

O M A R R I M A W IDepartment of Geology, University of Jordan, Amman, JordanN A D H I R A . A L - A N S A R IStrategic Environment and Water Resources Research Unit, Al-al Bayt U niversity, M afraq,JordanAbstract This study deals with water quality and salinization of theUpper Aquifer Complex in the northeastern part of the Mafraq areawhere, due to intensive agricultural activity and low annual rainfall,groundwater is intensively exploited for irrigation purposes. During thelast two decades, more than 5000 water samples have been collected,and analyses for the major cations and anions have been undertaken bythe M inistry of Water and Irrigation and the University of Jordan .Results reveal that the salinity of the water has increased from 300 uScm"1 in most of the area under investigation during early seventies tomore than 8000 uS cm'1 at certain localities. Increases of similarmagnitude were also recognized for Na, Ca, Mg, K, CI, S0 4 and N0 3 .The increase in ion concentrations (except N0 3) is attributed to leachingof soils subject to intensive furrow irrigation . The inc rease in N 0 3concentration from 10 mg l"1 to 90 mg I"1 during the same period isbelieved to be due to the leaching of fertilisers (chemical and organic)which are intensively used in the area. In order to protect furtherdegradation of groundwater quality, furrow irrigation has been replacedby the drip irrigation method in most of the area. In addition, a newwater management program has been adopted very recently to ensureminimum water abstraction.

I N T R O D U C T I O NThis study is concerned with the hydrochemical development of groundwaterresources in the northeastern part of the Mafraq area in Jordan, which is a region oflow annual rainfall (150-200 mm) and intensive agriculture where more than 600wells have been drilled during the last two decades (Fig. 1). The area is underlain bythe Upper Aquifer complex, which mainly comprises basaltic rocks of Tertiary ageand silicified limestones of Upper Cretaceous age, has been utilized for itsgroundwater resources since the early 1970s. Increasing demand for in situagricultural activities and for domestic purposes has led to the abstraction of largequantities of water (80 X 106 m 3 year"1) since the mid 1970s. The safe yield of thearea is estimated to be of the order of 28 x 106 m 3 year"1 (El-Naser,' 1991; GTZ-WAJ, 1995). Water quality is deteriorating rapidly as a consequence of theexploitat ion of the groundwater reserves.


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236 Omar Rimawi & Nadhir A. Al-Ansari

'.< W e l l H r . ( H a t e r A u t h o r i t y L i s t )Fig. 1 Map showing the location of the study area and groundwater contour map.

HYDROGEOLOGYThe basalt aquifer and the Amman-Wadi Sir aquifer are the main aquifers of thestudy area, although the former is the major system. In the northern and eastern partsof the study area, a succession of six lava flows lies unconformably on thesedimentary rocks of the Late Cretaceous Balqa and Ajlun Group (Bender, 1968).The southern limit of the basalt aquifer is the Azraq basin while the eastern limit hasnot been defined at Safawi. The western limit of the aquifer reaches Mafraq andWadi Dhuleil, while it extends to Jabel El Arab in Syria in the north.The transmissivity of the aquifer ranges between 2.3 X 10"5 and 1.2 m2 s"1. Thebasalt aquifer together with the Wadi Sir (A7) and Amman (B2) aquifers form acomposite system within the western part of the study area. The transmissivity of thissystem ranges between 2.2 X 10"5 and 7 x 10"3 m2 s"1 with an average of 3.2 x10"4m2 s"1. The water is transferred laterally or vertically from the basalt aquifer intothe Amman-Wadi Sir aquifers. Similar conditions are noticed in the Dhuleil-Hallabatarea (Rimawi, 1992; Abu Sharar & Rimawi, 1993).

The groundwater contour map of the area (Fig. 1) shows two groundwaterplateaux. The first lies in the southeastern part (between contours 525 and 520 m)while the second is located in the middle part of the study area (between contours510 and 500 m). The general trend of flow in the former is from the east and west(groundwater recharge area) towards the north. The second plateau has a relatively


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Groundwater degradation in the northeastern part ofMafraq area, Jordan 237

higher groundwater gradient than the first which reflects the occurrence of differenthydraulic properties across the study area. Groundwater flows in two main directionsfrom the second plateau, namely towards the northwest and the southwest. The latterdirection is almost parallel to the groundwater flow lines from the Jabel El Arabarea. The Amman-Wadi Sir aquifer system in the middle part of the study area ischaracterized by low permeability and specific capacity compared with the basaltaquifer in the eastern parts.

HYDROCHEMISTRYThe hydrochemical data used in this study comprises information abstracted from theopen files of the Water Authority and samples collected recently by the authors. Thechemical analysis of samples collected from more than 400 wells during the last twodecades were checked by calculating the analytical error. All samples having morethan 5% analytical error were excluded, and as a result only 5148 complete chemicalanalyses were available to the present study. The parameters analysed consisted ofpH, EC, Ca, Mg, Na, K, CI, HC0 3 , C 0 3 , S0 4 and N0 3 .The chemical analysis data were subjected to descriptive statistical tests, and theresults are presented in Table 1. Results were also plotted (Fig. 2) in the form of aPiper diagram (Piper, 1944) which allowed classification of the groundwaters,according to Langguth (1966), into the following types:(a) First type: alkaline water with bicarbonate as the dominant ion,(b) Second type: alkaline water with bicarbonate and chloride as the dominant ions,(c) Third type: alkaline water with an increased proportion of alkali earths andchloride and sulphate as the dominant ions,(d) Fourth type: alkaline water with chloride as the dominant ion.The first two water types correspond to fresh groundwater, which originates ascontemporary recharge and sometimes as fresh water that percolates over shortdistances within the aquifer, or they represent unpolluted water (Rimawi, 1992). Thethird and fourth types correspond to fresh-brackish water of non-contemporary orTable 1 Descriptive statistics of the analysed and calculated parameters based on 5148 samples.ParameterEC (uS cm"1)PHTDS (mg l'1)Ca (meq l"1)Mg (meq l'1)Na (meq l"1)K (meq l"1)CI (meq l"1)S 0 4 (meq f )C 0 3 (meq l"1)H C 0 3 (meq l"1)N 0 3 (mg I"1)

Minimum0.316.41195.20.390.290.40.010.260.030.000.290.00

Maximum11.48.487771.833.638.073.02.2

96.5533.50.398.9598.0

Arithmeticmean1.367.63774.34.323.855.360.187.542.110.013.5633.91

Standarddeviation1.110.33644.43.194.045.190.139.262.620.051.5824.71

Coefficient ofvariation0.810.040.830.741.050.970.741.231.253.960.440.72


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238 Omar Rimawi & Nadhir A. Al-Ansari

Fig. 2 Results of chemical analysis presented on a Piper diagram.

almost ancient recharge (Salameh & Rimawi, 1984), which ascends from deepaquifers along major faults, or originates through fresh water mixing with salinewater that passes through evaporites (Rimawi & Udluft, 1985).The water chemistry data were investigated by cluster analysis using a computerprogram (Clusy, 1986). This technique involves the grouping together of similarentities together, g-mode clustering was used instead of the i?-mode as advocated byAshley & Lloyd (1978). Ionic ratio characteristics of the seven clusters and theirstatistics are shown in Tables 2 and 3, respectively.Cluster I represents the original percolated water while cluster II is developedfrom this water by further dissociation or partial mixing with other water types ofhigher ionic concentrations. The high concentration of nitrates (40 mg l"1) indicatesthat cluster III water is polluted, and it is believed that the source is irrigation returnflows. Water belonging to cluster IV is similar to that of cluster III apart from havinga higher salinity. Water of clusters V, VI and VII are similar in general, but there aredifferences with respect to their salinities.


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Groundwater degradation in the northeastern part of Mafraq area, Jordan 239

DISCUSSIONThe high correlation coefficient of EC with CI content in all clusters (Table 4)indicates that chloride contributes relatively more to the salinity than other ions.Furthermore, the contribution of Na to groundwater salinity is generally less thanthat of Ca and Mg. It was also noticed that for the same specific EC values, Naconcentration might vary. The high Na content in some samples is derived fromcation exchange process between Ca-HC0 3 water and sodium rich zeolites within thebasaltic aquifer. Sodium is usually released to the water, and calcium ions will befixed by zeolites.

Table 2 Ionic ratio characteristics of different clusters identified in the database.Cluster numb er Characteristic features

1 Ca > Mg > Na > K, HC 0 3 > Cl > S0 4 > N 0 3(Ca + Mg)/(Na + K) > 1, (Na - C1)/S04 < 1, Na/Cl < 1II Na > Mg >C a > K, Cl > HC 0 3 > S 0 4 > N 0 3(Ca + M g)/(Na + K) < 1, (Na - C1)/S04 < 1, Na/Cl > 1III Na > Ca > Mg, Cl > HC 0 3 > S0 4(Ca + Mg)/(Na + K) > 1, (Cl - Na )/S0 4 < 1IV Na > Ca > Mg > K, Cl > S0 4 > HC0 3

(Ca + Mg)/(Na + K) < 1, (Cl - Na)/Mg < 1V Na > Mg > Ca, Cl > S0 4 > HC0 3(Ca + Mg)/(Na + K) < 1, (Cl - Na)/Mg > 1VI Na > Mg > Ca, Cl > S0 4 > HC0 3(Ca + Mg)/(Na + K) > 1, (Cl - Na)/Mg > 1VII Na > Mg > Ca, Cl > S0 4 > HC0 3

Table 3 Average values of the chemical parameters for the different clusters.ParameterEC (uS cm"1)pHTDS (mg I"1)Ca (meq l'1)Mg (meq l"1)Na (meq l"1)K (meq l"1)Cl (meq l"1)S0 4 (meq f )H C 0 3 (meq 1')N 0 3 (mg r 1 )No. of samples

6937.503932.103.471.420.111.680.584.6010.01591

7247.894251.591.663.730.143.071.182.6817.01201

13087.567292.954.465.370.176.601.744.0341.71189

Cluster2053

7.5811595.055.349.690.23

12.433.853.2846.6512

30947.70170010.738.4211.130.39

22.585.01.8363.4390

44137.62251914.6612.3017.730.42

32.858.412.2648.0204

69197.46428824.1420.4331.050.50

55.4516.372.1948.846


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gw degradation in the northeastern part of mafraq.pdf

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