Stagnant aquifer concept Part 3. Stagnant miniaquifers in the stage of formation, Makhtesh Ramon, Israel

Vladimir Fridman, Emanuel Mazora, Alexander Becker, Dudik Avraham, Eilon Adar

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Observation wells in the arid Ramon National Geological Park were monitored at three sites (C, T, and E), each with wells spaced tens of meters apart, the distances between the sites being 860-1060 m. The following characteristics were observed: (1) water level differences of up to a few meters occur between wells that are 20-60 m apart at each site, and level differences of over 10 m occur between wells at the three sites, (2) the water levels were steady over 2 years of monitoring, (3) Cl concentrations in the wells vary over three orders of magnitude: 0.4-1.8 g 1-1 in site C, 1.8-3.7 g 1-1 in site T, and 2.5-13 g 1t1̄ in site E, (4) the relative abundance patterns of the dissolved ions vary remarkably along with the concentration variations, from water dominated by Ca and SO4 to water dominated by Na and Cl, (5) the chemical composition is steady in each well, as indicated by chemical analyses repeated over 6 years, and conductivity monitoring over 2 years. The observed significant and steady compositional differences are interpreted as indicating the existence of small-scale isolated aquifers, with no lateral flow between them in spite of the pronounced water level differences. Flow in fractures is ruled out because of the steady water levels and very slow water level recovery in pumped wells. Dating strongly confirmed the lack of flow in the investigated shallow system. A well situated in the flood plain of Nahal Ramon revealed a tritium concentration of 8 TU and 14C concentration of 69 p.m.c. - indicating post-1954 water, but two wells outside the river bed contained no measurable tritium and 14C values of 14 and 22 p.m.c. - indicating water ages in the order of 10 000 years. In 15 additional wells no measurable tritium was determined. Thus, a case of ancient groundwater trapped in shallow aquifers, and bounded by efficient hydraulic barriers, is demonstrated. The geological set up seemed rather homogeneous, with no clue to small-scale efficient hydrological barriers. Yet, a detailed geological study, conveyed in the light of the hydrochemical findings, revealed the existence of dykes and small-scale structural and lithological controls, coinciding with some of the hydraulic discontinuities defined by the water properties.

Original languageEnglish
Pages (from-to)263-282
Number of pages20
JournalJournal of Hydrology
Volume173
Issue number1-4
DOIs
StatePublished - 1 Jan 1995

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