Cross-Formational Rising Groundwater at an Artesian Kartic Basin, the Ayalon Saline Anomaly, Israel
Amos Frumkin and Haim Gvirtzman

 

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ABSTRACT

Figure 1

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It is proposed that a geothermal artesian karstic system at the central part of the Yarkon-Taninim Aquifer creates the 'Ayalon Saline Anomaly' (ASA - Fig. 1), whose mechanism has been under debate for several decades. A 4-years-long detailed groundwater monitoring was carried out at 68 new shallow boreholes in the Ayalon region, accompanied by a comprehensive survey of karstic voids. Results indicate the rising of warm-brackish groundwater through highly permeable swarms of karstic shafts, serving as an outflow of the artesian geothermal system. The ASA area contains "hot spots", where groundwater contrasts with 'nornal' water hundreds of meters away (Fig. 2). The ASA temperature reaches 30oC (~5oC warmer than its surroundings), chloride concentration reaches 528 mg/l (50-100 mg/l in the surrounding), H2S concentration reaches 5.6 mg/l (zero all around) and pH value is 7.0 (compared with 7.8 around). Subsequently, the hydrothermal water flows laterally of at the water-table horizon through horizontal conduits, mixing with 'normal' fresh water which had circulated at shallow depth. A new great cave was found as well at the water table region (Fig. 3). Following rainy seasons, maximal water-table rise is observed in the ASA compared to its surroundings. Regional hydrogeology considerations suggest that the replenishment area for the ASA water is at the Samaria Mountains, east of the ASA. The water circulates to a great depth while flowing westward, and a cross-formational upward flow is then favored close the upper sub-aquifer's confinement border.

 



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