HU - Hydrogeology and Environment

Journal of the Dept. of Hydrogeology and Environment, University of Würzburg (ISSN 09309-3757)

Editorial office: BGI, Greisingstr. 8, 97074 Würzburg, GERMANY

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Vol. 26 (2001)


Vol. 26: 

Hydrochemistry and Isotope Hydrology of Groundwater Resources in the Hammad Basin (Jordan)

Mutewekil Obeidat

Hydrochemical and isotopic investigations of groundwater resources in the Hammad basin have been carried out. Three aquifer units with different hydrochemical and isotopic characteristics were identified.
The groundwater of the Rijam aquifer of the upper system can be classified as fresh in Muqat-Ruweishid area and northwest Hammad and brackish in the other parts of the study area. The groundwater of the Amman-Ajlun and Triassic aquifers is classified as brackish water. The temperature gradient of Rijam groundwater is calculated to be 3.7 °C/100 m. The groundwater resources have been clustered in four main groups, differentiated from each other by the dominating anions and cations and their total dissolved solids contents.
Four geochemical mixing models of the Rijam groundwater with flood flow have been constructed. The results of simulation shows that the groundwater quality will be improved with increasing mixing ratio of flood water.
Isotopically, most of the groundwater resources falls below the Global Meteoric Water Line (GMWL) and far away from the Mediterranean Meteoric Water Line (MMWL), suggesting that the waters are ancient and were recharged in a different climate other than Mediterranean. The groundwater of Triassic and Amman-Ajlun aquifers is depleted with respect to stable isotopes in comparison with that of Rijam aquifer. The Deep Hammad (Amman-Ajlun aquifer) has the most depleted stable isotope values ever recorded in Jordan.
Excluding groundwater of the Rijam aquifer in the unconfined section, the groundwater resources in the Hammad basin are nontritiated. This indicates a pre-1952 recharge history. Conventional age of Rijam groundwater ranges from 22000a before present to more than 48000a. The groundwater of the Rijam aquifer from Muqat-Ruweishid area has conventional age which is lower than that from the other parts of the study area and of the same aquifer. This groundwater is tritiated signifying mixing of old and recent water. Generally, the pumped groundwater from the study area does not contain recently recharged water and consists mainly of palaeowater recharged during past pluvials (fossil groundwater). Using isotope techniques, mixing of two water groups have been proved. The calculated mixing ratio is about 50 %.
The groundwater recharge to the upper aquifer system was estimated using the computer program MODBIL (Udluft, 1994) to be 1.1 mm/a, representing 1.48 % of the long term precipitation. Recharge estimation using the chloride method resulted in 0.11 mm/a average value. This represents recharge through soil matrix and should be taken as semiquantiative, as the ZFP could be located at higher depths. Recharge can take place through macro pores, which are not considered in this study. Deeper soil profiles should be taken. Groundwater pumped from the unconfined section of the Rijam aquifer east of the Hammad basin was modeled to contain recent water in the range of 1.5 to 3 %.
Using a GIS environment, elevation and slope models for the study area were constructed. The different chemical and isotope parameters have been presented and integrated concerning geology, groundwater levels and groundwater flow direction.

Paper language: english

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