Vulnerability mapping of shallow groundwater Ali El-Naqa ... · Vulnerability mapping of shallow...

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Introduction The dramatic increase in Jordan’s population and the improving living standards demand an increase in water supplies, with resulting increases in the amounts of wastewater and irrigation return flows. Subsequently, all available water resources are used including overex- ploited aquifers. The agricultural sector is the major user of groundwater resources in the study area. More than 94% of the total groundwater withdraw is used for irrigation. According to Water Authority of Jordan (WAJ), agricultural water use increased from 238 mil- lions cubic meters (MCM) in 1985 to 320 MCM in 1995 in the Jordan Valley. The demands for irrigation water are not only due to increasing agricultural activities, but also to a large extent to wasteful and inefficient Mustafa Al Kuisi Ali El-Naqa Nezar Hammouri Vulnerability mapping of shallow groundwater aquifer using SINTACS model in the Jordan Valley area, Jordan Received: 20 April 2005 Accepted: 21 February 2006 Published online: 21 March 2006 ȑ Springer-Verlag 2006 Abstract Jordan Valley is one of the important areas in Jordan that in- volves dense agricultural activities, which depend on groundwater re- sources. The groundwater is exploi- ted from an unconfined shallow aquifer which is mainly composed of alluvial deposits. In the vicinity of the Kafrein and South Shunah, the shallow aquifer shows signs of con- tamination from a wide variety of non-point sources. In this study, a vulnerability map was created as a tool to determine areas where groundwater is most vulnerable to contamination. One of the most widely used groundwater vulnera- bility mapping methods is SINT- ACS, which is a point count system model for the assessment of groundwater pollution hazards. SINTACS model is an adaptation for Mediterranean conditions of the well-known DRASTIC model. The model takes into account several environmental factors: these include topography, hydrology, geology, hydrogeology, and pedology. Spatial knowledge of all these factors and their mutual relationships is needed in order to properly model aquifer vulnerability using this model. Geographic information system was used to express each of SINTACS parameters as a spatial thematic layer with a specific weight and score. The final SINTACS thematic layer (intrinsic vulnerability index) was produced by taking the sum- mation of each score parameter multiplied by its specific weight. The resultant SINTACS vulnerability map of the study area indicates that the highest potential sites for contamination are along the area between Er Ramah and Kafrein area. To the north of the study area there is a small, circular area which shows fairly high potential. Else- where, very low to low SINTACS index values are observed, indicating areas of low vulnerability potential. Keywords Vulnerability Ground- water Pollution SINTACS model Jordan Valley Environ Geol (2006) 50: 651–667 DOI 10.1007/s00254-006-0239-8 ORIGINAL ARTICLE M. Al Kuisi (&) Department of Applied Geology and Environment, Faculty of Science, University of Jordan, P.O. Box 430616, 11143 Amman, Jordan E-mail: [email protected] Tel.: +962-777-499510 Fax: +962-6-4734169 A. El-Naqa N. Hammouri Faculty of Natural Resources and Environment, Hashemite University, P.O. Box 150459, Zarqa, Jordan E-mail: [email protected] E-mail: [email protected]

Transcript of Vulnerability mapping of shallow groundwater Ali El-Naqa ... · Vulnerability mapping of shallow...

Page 1: Vulnerability mapping of shallow groundwater Ali El-Naqa ... · Vulnerability mapping of shallow groundwater aquifer using SINTACS model in the Jordan Valley area, Jordan Received:

Introduction

The dramatic increase in Jordan’s population and theimproving living standards demand an increase in watersupplies, with resulting increases in the amounts ofwastewater and irrigation return flows. Subsequently, allavailable water resources are used including overex-ploited aquifers. The agricultural sector is the major user

of groundwater resources in the study area. More than94% of the total groundwater withdraw is used forirrigation. According to Water Authority of Jordan(WAJ), agricultural water use increased from 238 mil-lions cubic meters (MCM) in 1985 to 320 MCM in 1995in the Jordan Valley. The demands for irrigation waterare not only due to increasing agricultural activities, butalso to a large extent to wasteful and inefficient

Mustafa Al Kuisi

Ali El-Naqa

Nezar Hammouri

Vulnerability mapping of shallow groundwateraquifer using SINTACS model in the JordanValley area, Jordan

Received: 20 April 2005Accepted: 21 February 2006Published online: 21 March 2006� Springer-Verlag 2006

Abstract Jordan Valley is one of theimportant areas in Jordan that in-volves dense agricultural activities,which depend on groundwater re-sources. The groundwater is exploi-ted from an unconfined shallowaquifer which is mainly composed ofalluvial deposits. In the vicinity ofthe Kafrein and South Shunah, theshallow aquifer shows signs of con-tamination from a wide variety ofnon-point sources. In this study, avulnerability map was created as atool to determine areas wheregroundwater is most vulnerable tocontamination. One of the mostwidely used groundwater vulnera-bility mapping methods is SINT-ACS, which is a point count systemmodel for the assessment ofgroundwater pollution hazards.SINTACS model is an adaptationfor Mediterranean conditions of thewell-known DRASTIC model. Themodel takes into account severalenvironmental factors: these includetopography, hydrology, geology,hydrogeology, and pedology. Spatial

knowledge of all these factors andtheir mutual relationships is neededin order to properly model aquifervulnerability using this model.Geographic information system wasused to express each of SINTACSparameters as a spatial thematiclayer with a specific weight andscore. The final SINTACS thematiclayer (intrinsic vulnerability index)was produced by taking the sum-mation of each score parametermultiplied by its specific weight. Theresultant SINTACS vulnerabilitymap of the study area indicates thatthe highest potential sites forcontamination are along the areabetween Er Ramah and Kafreinarea. To the north of the study areathere is a small, circular area whichshows fairly high potential. Else-where, very low to low SINTACSindex values are observed, indicatingareas of low vulnerability potential.

Keywords Vulnerability Æ Ground-water Æ Pollution Æ SINTACSmodel Æ Jordan Valley

Environ Geol (2006) 50: 651–667DOI 10.1007/s00254-006-0239-8 ORIGINAL ARTICLE

M. Al Kuisi (&)Department of Applied Geologyand Environment, Faculty of Science,University of Jordan, P.O. Box 430616,11143 Amman, JordanE-mail: [email protected].: +962-777-499510Fax: +962-6-4734169

A. El-Naqa Æ N. HammouriFaculty of Natural Resourcesand Environment, Hashemite University,P.O. Box 150459, Zarqa, JordanE-mail: [email protected]: [email protected]

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irrigation usage or management. Moreover, irrigationefficiency is substantially low and thus the averagecoefficient of efficiency in agriculture in the Jordan valleyis about 56% (ISPANE 1994, USAID 1995). This meansa 44% water loss through irrigation.

The climate in the Jordan Valley area is consideredsemi-arid. Soils are composed mainly of alluvial sedi-ments poor in organic matter. Fertilizers and agriculturalchemical compounds are intensively used to maintain theproductivity of the soil. Therefore, the unconfined shallowaquifer is showing signs of contamination from a widevariety of non-point sources (NPS) (Al Kuisi 1998). Thenitrate concentration in the groundwater ranges between14.52 and 52.84 mg/l with an average value of 40.66 mg/l(Al Kuisi 1998). This issue will be discussed later ingroundwater chemistry section.

Assessing the behavior of NPS pollutants is complexbecause of the heterogeneity of conditions in thesubsurface system and the spread over large areas atrelatively low concentrations. Therefore, most aquifer

contamination from non-point contribution is discov-ered only after the water supply sources have beenaffected.

Vulnerability maps are frequently used to prioritizeareas where groundwater protection or monitoring iscritical. This approach is also useful to evaluate land-useactivity with respect to the development of pollutionliability insurance and assessment of economic impactsof disposal costs in highly vulnerable areas.

The concept of groundwater vulnerability is based onthe assumption that the physical environment mayprovide some degree of protection against impacts ofcontaminants entering the subsurface zone. Conse-quently, some land areas are more vulnerable togroundwater contamination than others. Groundwatervulnerability maps show areas of the greatest potentialfor groundwater contamination on the basis ofhydrogeologic and anthropogenic factors, and conse-quently classify targeted areas into units with varyinglevels of vulnerability.

Fig. 1 Location map of thestudy area

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Description of study area

The study area extends from the middle to the southernregion of the Jordan Valley. The overall study area liesbetween 31�40¢52¢¢ and 31�49¢40¢¢ North and 35�32¢00¢¢and 35�42¢06¢¢ East (Fig. 1). The area has a semi-aridclimate with mean annual rainfall range between 100and 150 mm, and mean annual temperature varyingfrom 19 to 36.5�C. The irrigation in the study area relieson waters from the Zarqa River (King Talal Dam Res-ervoir) and a mixture of waters from the Zarqa Riverand the King Abdullah Canal. The highest amount ofreclaimed water (RW) used for irrigation comes fromthe overloaded Khirbet As-Samra wastewater treatmentplant (WWTP), where the wastewater from Amman,Zarqa, and Ruseifa is treated. Its RW is discharged intoZarqa River and then King Talal Reservoir (KTR) (AlKuisi 2005).

In addition, irrigation waters in this area are sup-plemented by groundwater produced from differentprivate wells. According to WAJ, there are more than122 wells in the northern part and 102 wells south of thestudy area (WAJ 2004).

In the southern region, the farmers are mostlydependent on groundwater for irrigation due to the

characteristic semi-arid climate with irregular short-termrainfall only during the winter period. Mean annualrainfall is less than 100 mm/yr. About 99% of the 102wells in this region are used for irrigation purposes andproduce water from the shallow aquifer system (WAJ2004).

Geology of the study area

Outcropping rocks of the Triassic, Jurassic, and Creta-ceous ages are distributed mainly on the foothills, theescarpment, and the highlands in the study area.Tertiary and Quaternary deposits cover the rift valley.Table 1 and Figure 2 show the different geological for-mations in the study area. The following paragraphdescribed the different lithostratigraphical units in thestudy area.

The Triassic–Jurassic systems consist of the ZerqaGroup, which is subdivided into two formations: theMain Formation (Z1) of Triassic age and the AzabFormation (Z2) of Jurassic age. The Lower Cretaceousrocks consist of Kurnub Group (k), it lies unconform-able with erosinal unconformity on the Azab Formationof Jurassic sediments. The Lower Cretaceous starts withbasal conglomerates or sandstone intercalated with

Table 1 Simplified hydrogeological classification of the rock units in the study area (JICA 1995)

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conglomerate layers up to 5 m in thickness, followed byvaricolored alternating silty and marly, coarse to med-ium and fine grained sandstones with some shale andgypsum.

The Kurnub Group consists of two units, the lowermassive white sandstone with thin dolomite and shalebands and the upper varicolored sandstone containingthin intercalations of limestone, shale, dolomite, andmarl. The average thickness of this group is reported tobe about 300 m (Bender 1974).

The Upper Cretaceous was divided by Quennel(1951) into two groups a lower Ajlun Group and anupper part, Belqa Group. The Ajlun group includes allthe marine sediments of Cenomanian–Touranian age. Itis represented by a sequence of carbonates consistingmainly of limestone, dolomite, marl, shale, andsometimes sandstone. The group reaches its maximumthickness which ranges between 500 and 550 m in thenorthern part of Jordan and thins gradually towards theZerqa River. It also increases westwards towards theescarpment of the Jordan Dead Sea Rift Valley (Bender

1974). Masri (1963) initially subdivided this group intofive formations from bottom to top, the group was latersubdivided into seven lithostratigraphic subdivisions(A1–A7) by MacDonald et al. (1965) and Wolfart(1959). The subdivisions are based on water-bearingcharacteristics of the sediments separating the sequenceinto regionally important aquifers and aquicludes.

The Belqa Group is composed of all sediments fromthe Late-Turonian to Early-Oligocene. The dominantrocks types are chalks and marls with varying amountsof chert and phosphatic rocks. Although this group wasdivided by MacDonald et al. (1965) into four forma-tions, only two of them (B1 and B2) are known to existin the area.

The Jordan Valley Group includes all Tertiary sedi-ments outcropping in the Jordan Valley and along theRift side. These sediments are younger than the BelqaGroup. This formation locally consists of mainly con-glomerate and marl. Its deposits were associated withthe tectonism which formed the rift and include mate-rials of fluviatile and lacustrine origin.

Fig. 2 Geological map of thestudy area (Bender 1974)

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The Jordan valley group includes three formations:Shaquar Formation (JV1), Ghor El-Katar Formation(JV2), and Lisan formation (JV3). This group consistsmainly of conglomerates and marls and it lies un-con-formably on the other older systems and is overlain byQuaternary soil, sand and gravel. Outcrops of the for-mation are scattered along the foothills in the studyarea.

Finally, the Quaternary deposits cover most of theolder Jordan Valley deposits and are mostly derivedfrom the adjacent older rock units present at the valleyescarpments. Alluvium deposits are composed mainly ofcoarse to medium-grained gravels and sand near thegraben rims and fine sand and silt at the fringes of thealluvial fans. Downstream of the Kafrein dam thesedeposits are poorly sorted consisting of partially ce-mented gravels with talus and colluvium at the edge ofthe valley floor. Its permeability varies considerably dueto the variation in the cement and the percentage of thesilt-clay content.

Hydrogeology

The hydrogeological classification of rock formations inthe study area as well as in Jordan is presented inTable 1. The schematic hydrodynamic pattern ofgroundwater in Jordan is shown in Fig. 3. The aquifersystem in the study area can be differentiated into fourmain aquifers as follows from bottom to top: ZarqaAquifer, Lower Cretaceous Aquifer (Kurnub K), Upper

Cretaceous aquifer [Ajlun Group (A1/2–A7) and BalqaGroup (B1–B5)], and Jordan Valley Aquifer [Shallowaquifer (J)]. Groundwater in the first three aquifers oc-curs under artesian conditions where the artesian head ishigher than the aquifer thickness below ground surface.Therefore, groundwater discharges from these aquifersmostly occur under the effect of artesian pressure.

The groundwater flow in the upper aquifer complexdischarges along the slopes overlooking the Dead Sea ascold water springs (Fig. 3). The easterly orientedgroundwater flow infiltrates through the aquitardsdownward to the underlying lower aquifer sandstonecomplex. Infiltration takes place through the porositywithin the upper aquifer complex. As soon as the infil-trating water reaches the lower aquifer complex, itchanges its flow direction towards the west due to theinfluence of the ultimate base level, namely the Dead Sea(Salameh and Udluft 1985).

Fig. 3 Hydrodynamic pattern of the central part of Jordan(Salameh and Udluft 1985)

Table 2 Hydrogeological characteristics and volume (yield)abstraction for the selected wells (WAJ 2004)

Wellnumber

Welldepth(m)

Yield(m3/h)

Depthto water(m)

Total yield(m3/year)

Averagesalinity(lS/cm)

W1 103 42 71 373.800 2,550W2 102 50 70.5 186.900 1,120W3 106 76 73 252.200 3,140W4 74 90 60 243.000 3,220W5 50 100 18 135.000 4,220W6 337 90 37 191.400 970W7 60 75 17 224.200 1,960W8 90 75 19 186.900 3,620W9 90 63 40.8 235.500 1,120W10 85 51 41.45 382.800 1,100

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Jordan Valley shallow aquifer

The Jordan Valley Group fills the rift valley and formsthe wide valley floor. The thickness of the Jordan ValleyGroup is reported at more than 3,000 m in the Lisanarea to the south of the Dead Sea (JICA 1995). TheJordan Valley Group can be further divided into threegroups from the lower to the upper sections as follows:

• Consolidated cemented conglomerate layers of about100 m thickness;

• Conglomerate and alternating marl, sand, and gravellayers of about 350 m thickness; and

• Alternating marl, clay, chalk, silt and gypsum layersof more than 300 m thickness.

The upper zone represents the shallow aquifer whichextends along the Jordan Valley floor and consists ofalluvial fans and other recent sediments (Abed 2000). Thisshallow aquifer has a good potential and quality. How-ever, the groundwater of the upper aquifer deterioratestowards the west due to the presence of Lisan formation.

The upper part of this formation consists of alternationsof fine to medium particles of marl and clay with friablechalk, silt and gypsum. Hence, this part constitutes about70% of the Jordan Valley deposits (Bender 1974; Abed2000). While, the lower portion of Lisan formation iscomposed of dark grey and greenish marl with few sandlayers. The upper part of Lisan Formation is responsiblefor an increase in salinity of about 1,500–2,500 lS/cm. Inaddition, the permeability of the shallow aquifer rangesbetween 6.5·10)4 and 1.3·10)2 m/s, with an average valueof 6.6·10)3 m/s (JICA 1995).

The deep aquifer of the middle zone is intercalatedwith gravel, sand and silt with thicknesses of 90–100 m.The thickness increases towards the west where thesedeposits are intercalated with the Lisan formation,thereby resulting in a considerable increase in salinity.

A total of 224 (122 in the north and 102 in the south)wells have been drilled for irrigation and drinking pur-poses in the study area. Generally, the depth of these wellsranges between 20 and 377 mwith depth to water rangingbetween a few meters to more than 110 m (WAJ 2004).

Fig. 4 Digital elevation model(DEM) and location of waterwells

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Fig. 5 Rating curves for SINTACS method parameters (AfterCivita and De Maio (1997)

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For the hydrochemical studies, ten wells (six wells inthe northern and four wells in the southern region) weremonitored over a period of 2 years. Table 2 summarizesthe hydrogeological characteristics and the volume ofwater abstracted (yield) from these monitoring wells.Furthermore, 100 wells penetrating the shallow aquiferwere selected and sampled for their chemical constitu-ents. These include: Ca, Mg, Na, K, Cl, S, NO3, HCO3,and CO3, in addition to pesticides and trace elements

which include: Fe, Mn, Li, Ba, Sr, Ni, Pb, Cd, Cu, Br,and Zn.

Hydrochemical characteristics of groundwater

The development of groundwater resources in the Jor-dan Valley area started in the early 1960s. By that time,the quality of the water of the shallow aquifer was

Fig. 6 Depth to water table(S-parameter)

Table 4 Intrinsic vulnerability level of the aquifers (SINTACSindex)

Intrinsicindex level

NormalizedSINTACS index

Very low <25Low 25–39Medium 40–49High 50–75Very high >75

Table 3 Strings of weights and hydrogeological scenario inSINTACS (Civita and De Maio 1997)

Parameter I. Normal I. Relevant Drainage Karst Fissuring

S 5 5 4 2 3I 4 5 4 5 3N 5 4 4 1 3T 4 5 2 3 4A 3 3 5 5 4C 3 2 5 5 5S 2 2 2 5 4

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excellent for different uses. However, rapid increase inthe number of wells drilled for agricultural purposes ledto overexploitation and increasing salinity by the end ofthe 1960s and the beginning of the 1970s. However,there was a temporary decrease in the salinity of thewaters in the 1980s, which could be attributed to thesupplement of irrigation waters from the King AbdullahCanal and the subsequent reduction in the abstractionfrom the aquifer. The increasing salinity trends resumedin the 1990s with the obvious effects, such as saliniza-tion, due to overpumping and increased dissolved solidsof the irrigation waters.

The pollution factor characterizing the groundwaterfrom the shallow aquifer in the study area is nitrate. Thenitrate concentration was observed temporally throughthe ten selected wells. Its values were presented graphi-cally for the investigated period. Nitrate values rangedbetween 14.52 and 52.84 mg/l with an average value of40.66 mg/l. Nitrate concentrations rose steadily overtime in all the observed wells. As an example, the nitrateconcentration in well AB1130 increased from 33 mg/l inNovember 1971 to 109 mg/l in August 1996, which is

nearly triple the original value prior to 1971. This in-crease in nitrate concentrations could be attributed tothe fertilizer application in the study area as 99% of thefarmers used manure and urea fertilizers. On the otherhand, nitrate is very soluble and is dissolved by irriga-tion or rainwater and percolates deeper into the soilwhere it either enters the groundwater by direct perco-lation or, if it meets an impermeable layer such as clay,by sideways migration through the soil until it finds wayinto the groundwater.

SINTACS model

There are many groundwater pollution vulnerabilityassessment systems. Among these models, the SINTACSmethod used in this study was developed by Civita(1990, 1993, 1994) and Civita and De Maio (1997) toassess relative groundwater pollution vulnerability usingseven hydrogeologic parameters. It is an evolution of theUS DRASTIC model adapted to Mediterraneanconditions.

Fig. 7 Net recharge rating map(I-parameter)

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The parametric models like SINTACS belong to thepoint count system model group in which every factorhas not only its own score but also an additional weightto reduce or amplify its importance during the analysis.

The additional weight is set in relation to environ-mental characteristics, such as high dispersionphenomena from surface water bodies to groundwateror widespread pollution sources. The model takes intoaccount the following seven factors:

1. S water table depth;2. I effective infiltration;3. N unsaturated conditions;4. T soil media;5. A aquifer hydrogeologic characteristics;6. C hydraulic Conductivity; and7. S topographic slope.

Each factor is assigned a score that range between 0and 10 according to its importance in defining vulnera-bility (Fig. 5). Scores are then modified by weights whichare related to the specific environmental and/oranthropogenic conditions of the area.

The particular SINTACS model considers fourpossible conditions:

1. Normal areas;2. Areas with widespread pollution sources;3. Areas with intense water losses from hydraulic

networks towards aquifers;4. Areas with karstic phenomena; and5. Areas with fissuring phenomena.

Finally, an intrinsic vulnerability index I is calculatedby summing the product of scores by weights, accordingto the following expression:

ISINTACS ¼X7

i¼1Pi � Wi;

where is the Pi is the score of each of the sevenparameters that the method considers and Wi therelative weight.

This intrinsic vulnerability index (I) is divided into sixclasses as follows:

Fig. 8 Impact of vadose zone(N-parameter)

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1. I>210 very high vulnerability;2. 186<I<210 high vulnerability;3. 140<I<186 moderately high vulnerability;4. 105<I<140 medium vulnerability;5. 80<I<105 low vulnerability; and6. I<80 very low vulnerability.

SINTACS database

Each of SINTACS parameters has been expressed asthematic layer using ArcMAP 9.0. A PersonalGeo-database using ArcCATALOG was created to holddata for these parameters. Each thematic layer will bedescribed briefly as follows:

Depth to water table (S-parameter)

Depth to water is the distance between the groundsurface and the groundwater table level. The water level

map was made by interpolating information stored inwell’s database. These data were obtained from WaterInformation System at the Ministry of Water and Irri-gation in Jordan. Inverse distance weighting (IDW)method was used to interpolate depth to water param-eter and the other seven parameters of SINATCS model.Depth to water level data was obtained by subtractingthe ground surface elevation from the water level. Theground surface elevation data were obtained from thedigital elevation model (DEM) (Fig. 4). The rating forthese values was obtained from Fig. 5a. Figure 6 showsthe interpolated thematic layer for depth to water values.

Net recharge (infiltration): (I-parameter)

The effective infiltration plays a very significant role inaquifer vulnerability assessment; it is the difference be-tween total precipitation and the cumulative loss bydirect runoff and effective evapotranspiration. Netrecharge ratings were determined using the Soil Con-servation Service (SCS) method (SCS 1972) andhydrologic data (evapotranspiration and runoff).

Fig. 9 Rating of soil media(T-parameter)

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The SCS runoff curve number method is one of thesimplest and most efficient models to estimate thesurface runoff. The parameters that form the method aresimple and the mathematics can be easily implemented.The surface runoff according to this method is given by

Q ¼ ðP � IaÞ2

ðP � IaÞ þ S;

where Q is the runoff (mm), P, the rainfall (mm), S, thepotential maximum retention after runoff begins, and,Ia, the initial abstraction.

Initial abstraction: Are all losses before runoff begins?It includes water retained in surface depressions, waterintercepted by vegetation, evaporation and infiltration.

Among several expressions to compute initialabstraction, the following empirical equation will beused

Ia ¼ 0:2S:

Replacing Ia from this equation in the first equation willproduce

Q ¼ ðP � 0:2SÞ2

P þ 0:8S:

The parameter S is related to soil and cover conditionsof the watershed through the curve number (CN). Thisnumber can be given a value that range between 30 and100. The relation between S and CN is given by

S ¼ 1000

CN� 10:

The curve number is estimated for a drainage basinusing a combination of land use, soil, and antecedentsoil moisture condition. These parameters are given instandard SCS CN tables where suitable CN values aregiven for each of these conditions. Table 4 shows a partof standard SCS table.

Fig. 10 Hydrogeologiccharacteristics of the aquifer(A-parameter)

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The difference between the annual precipitation andrunoff represents the mean annual net recharge (mm/year). These values are rated according to an infiltrationrating chart (Fig. 5b). Figure 7 shows the interpolatedthematic layer of net recharge values.

Impact of the vadose zone: (N-parameter)

The impact of vadose zone was examined by interpretinggeological maps, drilling logs of groundwater wells andexcavation of trenches. The value of the impact of thiszone on the pollutants starting from the geolithologicalcharacteristics so the SINTACS score within everylithological unit is rated according to the relevantdiagram (Fig. 5e). Figure 8 shows the thematic layer ofthe impact of vadoze zone rating values that mainlyvaries between 1 and 2.

Soil media: (T-parameter)

Soil has a significant impact on the amount of rechargethat can infiltrate into the ground, and hence on the

ability of a contaminant to move vertically into thevadose zone. The presence of fine-textured materialssuch as silts and clays can decrease relative soil perme-ability and restrict contaminant migration. Soil infor-mation was obtained from the National Soil MappingProject conducted by the Ministry of Agriculture-Jordanin 1995 (Hunting Technical Services 1995). These datawere rated according to Fig. 5f. Figure 9 shows thespatial distribution of soil media rating over the studyarea.

Hydrogeologic characteristics of the aquifer:(A-parameter)

In vulnerability assessment methods, the aquifer prop-erties describe the process that takes place when a con-taminant becomes mixed with groundwater. The aquifertypology deals with the processes which take place belowwater level that is dispersion, dilution, absorption, andchemical reactivity of rocks: they are deeply influencedby the lithological kinds as well as by the permeabilityof the aquifer. Therefore, we must consider all these

Fig. 11 Hydraulic conductivityof the aquifer (C-parameter)

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characteristics to value the parameter. Starting from thedata available, it is attempted to find the best satisfac-tory values within the ranges shown by the SINTACSdiagram (Fig. 5g). Therefore, using the geolithologicalinformation prevailing in the study area, the aquifermedia was rated based on the rating chart (Fig. 5g).Rating distribution of aquifer media are shown inFig. 10.

Hydraulic conductivity of the aquifer: (C-parameter)

Hydraulic conductivity refers to the ability of the aquifermaterials to transmit water, which in turn controls therate at which ground water will flow under a givenhydraulic gradient. In this study, hydraulic conductivitywas obtained from pumping tests that have been car-ried by WAJ (2004). However, since the hydraulic

conductivity data are rarely available, the SINTACSmethod offers a direct approach to derive specific scoresfor hydraulic conductivity based on a diagram (Fig. 5c),where the main lithological units of the aquifer arerepresented together with the relevant values ofhydraulic conductivity. The rating distribution map ofthe hydraulic conductivity of the upper aquifer is shownin Fig. 11.

Slope or topography of land surface: (S-parameter)

The slope will determine the extent of runoff of thepollutant and the degree of settling sufficient forinfiltration. Slope information was extracted usingDEM. These slopes have been rated according to sloperating chart (Fig. 5d). The rating distribution oftopography slopes is shown in Fig. 12.

Fig. 12 Slope or topography ofland surface (S-parameter)

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SINTACS vulnerability map

The final SINTACS vulnerability thematic layer wasgenerated by summing each SINTACS thematicparameter. Each of these parameters has already beenmultiplied by its designated weight (Table 3).

The obtained index values range between 145 and186; however, to facilitate interpretation of the results,these ranges have been normalized to 0–100. This nor-malization allows six levels of classifications of vulner-ability, from very low to very high (Campagnoni andCarta 1997) (Table 4). Figure 13 shows the final result-ing vulnerability SINTACS thematic map.

The SINTACS index map shown in Fig. 13 indicatesthe general potential for polluting groundwater is veryhigh near the main reservoirs in the study area, such asWadi Shuayb and Kafrein Dams. The unsaturated zonein the adjacent areas of these two reservoirs is charac-terized by the presence of alluvial fans, mainly composedof unconsolidated gravels with sand and siltstones. Moreconcern must be given to cultivation of these areas; they

will absorb and retain pollutants more readily than theother areas. SINTAC vulnerability map was matchedwith dimethoate concentrations in groundwater wellsmeasured in the study area (Fig. 14). It was found thatareas with high vulnerability for groundwater contami-nation is in agreement with areas of high dimethoateconcentration. Finally, using this map in landuseplanning study would aid in avoiding further contami-nation of the groundwater by considering the vulnera-bility of an area before high-risk activities were allowedto take place.

Conclusions

Groundwater is inherently susceptible to contamina-tion from anthropogenic activities and remediation isvery difficult and expensive. Prevention of contami-nation is critical in effective groundwater management.In this paper, an attempt was made to assess aquifervulnerability in the Jordan Valley area.

Fig. 13 Intrinsic vulnerabilitymap using SINTACS

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The vulnerability of groundwater to contamination inthe study area was assessed using the SINTACS modelcombined with the geographic information system. Theresulting vulnerability index indicates that groundwaterresources in the surrounding area are susceptible topollution to a high degree as shown in Fig. 13. Thevulnerability map has a range from very high vulnera-bility to contamination to very low. The southern partsof the study areas are characterized by very high vul-nerability. The high vulnerability of these areas could be

attributed to the shallow water depth in this area, whichranges from a few meters to 10 m below land surfaceand a high recharge rate. In addition, the shallowaquifer in these areas consists mainly of intercalations ofgravel, sand, and silt deposits with shallow thickness.Furthermore, the aquifer materials are characterized byhigh hydraulic conductivity with an order of 10)3 m/s. Itwas found that the areas with high vulnerability forgroundwater contamination are in agreement with theareas of high dimethoate residues.

Fig. 14 Spatial distribution ofdimethoate residues (ng/l) ingroundwater

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