The study involved a selected area located between longitude 42˚00'00'' to 42˚30'00'' and latitude 32˚00'00'' to 32˚30'00'' with a total area of 2600 km² and elevation ranges between 280 and 360 meters above sea level Figure 1. The hydrogeochemical data of groundwaters of Um Erdhuma-Tayarat aquifer were examined to determine the factors that control the groundwater chemistry and the hydro-geochemical evolution.

Different geochemical interpretation methods were used to identify the geochemical characteristics. The study aims to estimate the hydrogeochemical processes using hydrochemical ratios and indices, also to determine the geochemical assessment and hydrochemical characteristics of the groundwater, which would be support planners in validating groundwater quality models. The area of investigation characterised by dry desert climate (dry Arid zone) during the second half of the twentieth century and the first decade of the twenty-first century [1] , where the mean annual values of rainfalls are not exceeding 50 mm in some dry years and little quantities of water may flow. The study area has undulating terrain with land surface rises gradually from the SE to the NW. The slope of the land surface varies between 0.4 and 13 m/km. Several valleys of seasonal flux forming plateaus with pediment deposits [2] and depression filled with sediments such as Habbariyia, Shabwan, and Khubrit Adhad. The valleys are defined as main landforms including Ubayidh valley and Tebal valley with its tributaries (Mdaycice, Abu Ghar, Shabwan, and Dwaykhla), these valleys form important drainage basins feeder to Um Erdhuma-Tayarat aquifer (groundwater recharge zone) (Figure 1).

The valleys and depressions fill sediments are considered as important geomorphologic units which classified within the scope of the territory eligible for agricultural activities. The depressions fill sediment overlies varying areas originated to the leaching of fractured dolomite and limestone rocks, where active runoff contributes in filling depressions by sands, mud, and silts.These valleys are characterized by expanding of widths, presence of old soils with gravels aggregates, karst sinkholes, rocks creep, and presence of meandering valleys with many break off in their long sectors.

In Habbariyia Depression, three stages of alluvial fans are developed. The higher two stages are highly dissected and separated from each other by a cliff. The two stages are probably of Pleistocene age. The third stage (youngest) is of smooth surface and might be of Early Holocene age. Structurally, the study area is located in the SE limb of Hauran anticlinorium (Rutba Uplift) within the Arabic-African plate [3] .

The uplift contributed to the tectonic movements within successive geological periods affects the structural and stratigraphic settings within Nukhaib Graben. Reference [4] described the N-S trending faults as a set of normal faults system with nearly 160 Kilometers in long and 60 Kilometers in wide forming Nukhaib Graben. Reference [5] presented an extended discussion concerning the geology and origin of Nukhaib Graben, using different geological, geophysical, and geochemical data. They pointed out that the graben is formed above the basement high of granitic intrusion and/or salt dome.

The software (Rockware-14) is used to determine the Hydro-structural model, based on geological data. The result of the model (Figure 2) shows the horizontal and vertical extension of geological formations within the geo-structural situation of the region related to the movement of the base blocks within Hail arch during Paleozoic. Also, Jurassic, Cretaceous, and Tertiary beds dip from 1.0˚ to 2.0˚ in a direction of ESE within the south eastern limb of Hauran anticlinorium.

Geological studies of [6] - [12] , are summarized in a spatial distribution map of the

Geologic Formations (Figure 3), and illustrated by vertical extensions as shown in the geological section A-B (Figure 4), where the study area includes Quaternary sediments, Zahra Formation, Dammam Formation, Erdhuma Formation, Tayarat Formation, Hartha Formation, Saadi Formation, Msad Formation, Rutba Formation, and Muhaywir Formation. More geologic details are mentioned in Table 1.

Groundwater occurs in different water bearing horizons of karistic fractured carbonate rocks belonging to Late Maestrichtian-Danian Formations (UmErdhuma-Tayarat aquifer). Regionally, al Hamad physiographic zone is considered as a main recharge zone of the aquifer within study area, [3] [14] , these studies confirmed a practical occurrence of recharge and water replenishment renewed aquifers by rain and runoff waters penetrated throughout rocks exposures within the valleys. Locally, UmErdhuma-Tayarat aquifer is recharged from Tebal-Ubayidh catchment area and from lateral leakage of waters passing as a result of hydraulic connection between adjacent aquifers. The amount of infiltration penetrated to UmErdhuma-Tayarat aquifer within study area is equal to:

In the interiors area restricted to Habbariyia-Nukhaib depression, UmErdhuma- Tayarat aquifer is of unconfined condition with saturation thickness ranged from 52 to 150 meters. The extensions of the aquifer are shown in Figure 2 and Figure 4.

The amount of permeability for the water bearing horizons of UmErdhuma-Tayarat aquifer ranged between 0.1 m/day and 14.7 m/day (Table 2). The aquifer is classified as aquifer of low to middle permeability compared with Laboutka classification [15] (Ta- ble 3).

The variation in the values of permeability originated to the heterogeneity of the rocks forming aquifers due to fractures density and intensity of karistification. Spatial distribution map of permeability (Figure 5), shows increasing in permeability variation grade ranged between 0.000011 and 0.0095 m/day/meter distance towards old Kasra

*Interpolated values.

and Abu Ghar with the extension of Fault trace (F3), whereas the permeability values decrease in area ESE Nukhaib town and its extensions within Habbariyia depression, whereas the transmissivity value decreases in the vicinity of Nukhaib, specifically in the East and Southeast direction. The groundwater of Um Erdhuma-Tayarat aquifer is controlled by unconfined conditions, where the amount of storativityranged from 10⁻³ to 5 × 10⁻² (Table 2) [16] - [18] .

The results of storage coefficient show low variation in values originated to the same geostructural settings and rocks characteristics. The spatial distribution variation of storativity shows an increasing in storativity variation grade ranged between 3.7 × 10⁻⁸ and 3.2 × 10⁻⁵ per meter distance towards Habbariyia extensions, whereas storativity value decreases in the vicinity of Nukhaib in the south part and new Kasra in north portion.

The amount of well productivity from UmErdhuma-Tayarat aquifer ranged between 162 m³/day and 2203 m³/day. Depending on Laboutka classification [15] , the wells within study area are classified within the wells of medium-very high productive.

The specific capacity of the water wells ranged between 1.8 and 21.1 liter/sec/m (Ta- ble 2) within wells depths ranged from 125 meters to 538 meters. The spatial distribution of specific capacity confirmed an increasing in variation grade ranged between 0.000003 and 0.0076 liter/sec/m (depth) per meter distance towards wells of Kasra in high to very high category of specific capacity classification while it decreases to low- medium category of specific capacity classification in the other part.

The groundwater flow model is determined throughout observation of groundwater levels (Table 2), using Groundwater Contour Software. The main hydrogeologic phenomena that deduced from the groundwater flow model (Figure 6), supported by equations No.1 and No.2 are briefly discussed as follows “The groundwater within UmErdhuma-Tayarat aquifer moves from the west and southwest portions in the area existed west Nukhaib graben and also flows from the north portion in the area located northeast Nukhaib graben towards Habbariyia region and its suburbs area. This region represents a groundwater discharge zone due to intense exploitation and/or deep percolation throughout buried sinkholes and karst passages forming a boundary of captured zone. The groundwater flows under the effort of hydraulic gradient (δh/δl) ranged from 0.000011 (11 cm/10 kilometers) to 0.007 (7 cm/10 meters), rate of groundwater flux ranged between 0.00000012 cm/day and 0.0066 cm/day and rate of groundwater pore velocity ranged from 0.000024 cm/day to 6.6 cm/day”.

, [19] (1)

where I: hydraulic gradient, K: permeability,

, [20] [21] . (2)

where V: groundwater Flux, s: specific yield or effective porosity,

The study was carried out based on the groundwater monitoring program in 24 wells within the scope of Habbariyia depression during 2013 water year. The coordinates are set by Garmin GPS. The groundwater levels measured by electrical sounder and rely on procedures in scientific references [22] - [25] . The processes of taking samples from wells were achieved according to the field procedures explained in the studies [26] [27] . All tools and bottles were washed with distilled water and then rinsed by sample water before packing to ensure the elimination of pollutants [28] [29] .

Groundwater pH and electrical conductivity are measured after taking samples using calibrated EC-pH meters with standard solutions. Groundwater samples were analyzed in Soil and Water Laboratory (Centre of the desert studies). Field measurements and analyses data base comprise total dissolve solids (TDS), total Hardness (H_T) and major ions were performed during same period of monitoring (June 2013). The chemical analyses of anions, cations, total dissolved solids (TDS) and total Hardness and field measurements are listed in Table 4.

Chemical composition reliability was checked using the charge balance method [21] . Groundwater quality and the hydrogeochemical mechanisms that affect the origin of groundwater and facies [30] are statistically assessed using the application of Curve expert v1.3 software. The groundwaters of the aquifers are classified based on hydrochemical ratios and saturation indices. Saturation indices (Table 5) of some common

CAI 1= [Cl − (Na + K)]/Cl; CAI 2 = [Cl − (Na + K)]/[SO₄ + HCO₃].

minerals were calculated using the program PHREEQC [31] . The interpretations of hydrochemical phenomena are done based on Piper trilinear, Durov plots and spatial analysis maps of hydrochemical variables using Groundwater Contour software. Also, Rockwork 14 is used in the preparation of hydrogeo-structural models, geologic map, and sections.

The study is concerned with the impact of hydrochemical processes on the groundwater quality within the aquifer. The hydrochemical processes that mostly influence the species of groundwater chemistry are leaching and dissolution of surface and subsurface weathered rocks with the effect of reverse and normal ion exchange throughout water-rock interaction (e.g. dolomitization and dedolomitization process). Also, the evaporation process and mixing action have a significant effect. Moreover, reduction oxidation process has no effect on the evolution of groundwater quality. Carbonate and sulphate mineral dissolution, with normal ion exchange reactions in 67 percentile of groundwater samples within UmErdhuma-Tayarat aquifer are the major hydrogeochemical processes responsible for the concentration of major ions in groundwater. Most groundwater samples of aquifer have Na/Cl ratio more than unity (67% of water points), reflects leaching of terrestrial salt facies (groundwater of meteoric origin). While the groundwater of aquifer that have Na/Cl ratio less than unity (33% of water points) reflects leaching of marine salt facies indicating that the mixing mechanism is the active process that impact the fossil groundwater of marine origin. Sulphate and chloride concentrations and depth to water table illustrates that water chemistry is impaired by land-use activities (geochemical affects with no impact of anthropogenic process). Groundwater samples of UmErdhuma-Tayarat aquifer are slightly saturated with respect to dolomite, slightly under-saturated with respect to aragonite. Fifty percent of groundwater samples are slightly saturated with respect to calcite. Whereas, all groundwater samples are slightly under saturated with respect to gypsum/anhydrite and moderately under saturated with respect to halite/sylvite. The majority of the groundwater types of UmErdhuma-Tayarat aquifer (91.5% of the total samples) belong to intermediate-more advanced grade of metasomatic sequence obtaining SO₄ > HCO₃ > Cl, SO₄ > Cl > HCO₃, Cl > SO₄ > HCO₃, and Cl > HCO₃ > SO₄ water types.

The first main conclusion that can be extracted from the hydrochemical interpretation strongly illustrates that rational plan for long-term and sustainable management of UmErdhuma-Tayarat aquifer cannot be only based on regulatory water quality targets.

So, a successful aquifer management plan will need to consider, the degree to which various waters currently encountered in the aquifer has complex mixtures between modern recharge waters, and ancient trapped fossil waters. The evolution of groundwater in the area could be explained, also by hydraulic properties and hydrodynamic behavior, such as groundwater flow through the strata of different mineralogical composition.

Hussien, B.M. and Faiyad, A.S. (2016) Modeling the Hydrogeo- chemical Processes and Source of Ions in the Groundwater of Aquifers within Kasra- Nukhaib Region (West Iraq). International Journal of Geosciences, 7, 1156-1181. http://dx.doi.org/10.4236/ijg.2016.710087