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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Bibliographic Details
Published in:Ground water 1997-01, Vol.35 (1), p.39-46
Main Authors: Remenda, V.H. (Queen's University, Kingston, Ontario, Canada.), Van Der Kamp, G
Format: Article
Language:English
Subjects:
AGUAS SUBTERRANEAS
ARENA
BENTONITA
BENTONITE
BROMURE
BROMUROS
CALIDAD DEL AGUA
CAPA FREATICA
Chemistry
CHLORURE
CLORUROS
CONTAMINACION
CONTAMINATION
CONTROLE CONTINU
EAU SOUTERRAINE
Environmental aspects
Experiments
Groundwater
MINERAL ARGILEUX
MINERALES DE ARCILLA
NAPPE SOUTERRAINE
Pollution
POTASIO
POTASSIUM
POZOS
PUITS
QUALITE DE L'EAU
SABLE
Sand & gravel
SASKATCHEWAN
Seals
SODIO
SODIUM
SOLUTE
SOLUTO
SULFATE
SULFATOS
TECHNIQUE DES TRACEURS
TECNICAS DE TRAZADORES
VIGILANCIA
Water, Underground
Wells
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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
ISSN:0017-467X
1745-6584
DOI:10.1111/j.1745-6584.1997.tb00058.x