Contamination from sand-bentonite seal in monitoring wells installed in aquitards
A six year field experiment has shown that a sand-bentonite mixture used to seal monitoring wells in aquitards contributes solutes to the ground water sampled from these wells. Monitoring wells were installed at field sites with hydraulic conductivity (K) ranging from 5 X 10(-9) m/s to 3 X 10(-11) m...
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Published in | Ground water Vol. 35; no. 1; pp. 39 - 46 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
Blackwell Publishing Ltd
01.01.1997
Ground Water Publishing Company |
Subjects | |
Online Access | Get full text |
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Summary: | A six year field experiment has shown that a sand-bentonite mixture used to seal monitoring wells in aquitards contributes solutes to the ground water sampled from these wells. Monitoring wells were installed at field sites with hydraulic conductivity (K) ranging from 5 X 10(-9) m/s to 3 X 10(-11) m/s. In most cases the boreholes remained dry during installation which allowed the placement of a dry powdered bentonite/sand mixture tagged with potassium bromide (KBr) to seal and separate sampling points. Over six years, wells were sampled periodically and ground-water samples were analyzed for Br and Cl and other major ions. Typical Br results ranged from 10 mg/l to 35 mg/l in the first 700 days, as compared to an estimated initial concentration in the seal material of about 75 mg/l. After six years the bromide concentrations had decreased to between 3 mg/l and 5 mg/l. The total mass of Br removed in six years is less than 50% of that placed; therefore the contamination effects, although considerably diminished, persist. The trends of Br, Cl, Na, and SO4 indicate that varying degrees of contamination occur. These data show that the materials used to seal monitoring wells in aquitards can have a significant and long-lasting impact on the chemistry of the water in the wells |
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Bibliography: | 9730074 P10 istex:F3059262DBDB1E6B41A55C0E3292AB480017C067 ark:/67375/WNG-3G3TGJQ9-J ArticleID:GWAT39 ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0017-467X 1745-6584 |
DOI: | 10.1111/j.1745-6584.1997.tb00058.x |