Entry from Directory of Selected Israeli Water-related Publications

TITLE:	Blocking and sealing of small diameter observation boreholes Rep.Hydro 1988/3
AUTHORS:	A. Melloul, I. Reingold, A. Dax
PUBLISHER:	Hydrological Service of Israel
PAGES:	46
PUBLICATION DATE:	July 1988
LANGUAGE OF PUBLICATION:	Hebrew
ABSTRACT:	The report presents the results of two field surveys on the blocking of small diameter observation boreholes and on its effect on the hydraulic contact between the borehole and the aquifer. The first survey included 280 boreholes in which the bottom of the borehole was measured. By comparing the measured depth with the original one, and by knowing the location of the perforated section of a borehole, it could be concluded whether the well is blocked and which part of the perforation is still open. The second survey included slug tests in 110 boreholes. Analysis of the data led to the finding that the decline of water level in the borehole during a slug test can be represented by an exponential decay function. The decay coefficient, or its reciprocal - the decay time, can serve as a measure of the extent to which the hydrograph of the borehole corresponds to that of the groundwater in the vicinity of the borehole. Although a positive correlation was found between the level of blocking of a borehole and its efficiency as an observation well, periodically repeated slug tests are necessary for providing a quantitative measure of the behavior of its hydrograph and for following up changes in the value of this measure as time goes on. The results of the surveys suggest that high Cl concentrations expedite corrosion and destruction of corrosive casings. It was also found that the presence of clay or loam within the perforated section enhance blocking of the borehole.
ADDRESS FROM WHICH THE PUBLICATION CAN BE OBTAINED:	Library, Hydrological Service, P.O.Box 6381, Jerusalem 91063, Israel
AVAILABILITY:	At request

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