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Two large-scale sealing experiments were conducted at Atomic Energy of Canada Limited's Underground Research Laboratory at Lac du Bonnet, Manitoba. The rate of water uptake in densely compacted sand–clay buffer materials proposed for use in a deep geologic repository for spent nuclear fuel was monitored. The buffer–container experiment examined the influence of heat on the performance of a large mass of buffer. Temperatures, water contents, and total and hydraulic pressures within and surrounding the installation were monitored for approximately 2.5 years. Local groundwater pressures increased as a result of rising temperatures. Water uptake and redistribution occurred in the buffer due to drying shrinkage close to the heater and counter-acted swelling due to an increase in water content near the rock–buffer interface. The isothermal test (ITT) allowed natural groundwater uptake from the surrounding rock mass under isothermal conditions. It was monitored for a period of 6.5 years and is the first, and longest running test of its kind yet conducted in the world. During its operation, the ITT (for as yet unconfirmed reasons) experienced a 35% decrease in the rate of water supply relative to that measured prior to experiment installation. This decrease impacts on the time required for saturation to be achieved.Key words: buffer, bentonite, underground research laboratory, instrumentation.Deux essais d'étanchéité à grande échelle ont été conduits au Laboratoire de recherche souterrain de l'Énergie atomique du Canada au lac du Bonnet, Manitoba. On a mesuré la vitesse d'absorption d'eau dans des matériaux tampons formés de sable et argile densément compacts devant être utilisés dans un dépôt géologique profond pour le combustible nucléaire irradié. L'expérience tampon–conteneur a permis d'examiner l'influence de la chaleur sur la performance d'une large masse de tampon. Les températures, teneurs en eau, pressions totales et hydrauliques à l'intérieur et autour de l'installation ont été mesurées durant environ 2,5 années. Les pressions de l'eau souterraine locale ont augmenté à cause de l'augmentation de la température, une absorption et une redistribution se sont produites dans le tampon à cause du séchage et du retrait près des points chauds d'une part, et de l'action inverse du gonflement dû à l'augmentation de la teneur en eau près de l'interface roc–tampon d'autre part. L'essai isothermique a permis l'absorption de l'eau souterraine naturelle venant du massif rocheux dans des conditions isothermiques. Des mesures ont été prises durant une période de 6,5 années, et cet essai est le premier et le plus long essai de ce type à être réalisé jusqu'à ce jour dans le monde. Au cours de son opération, cet essai a subi, pour des raisons encore non confirmées, une diminution de 35 % de la vitesse de son alimentation en eau par rapport à celle mesurée avant la mise en place de l'expérience. Ceci a des impacts sur le temps requis pour atteindre la saturation.Mots clés : tampon, bentonite, Laboratoire de recherche souterrain, instrumentation.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

A number of fires involving polychlorinated biphenyl (PCB)-containing transformers and capacitors have occurred in the United States. PCB fires generate by-products such as polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs) and, when the transformer is in a building, contaminate the interior. Considerable concern exists over the potential human health effects associated with exposure by inhabitants to residual levels of PCBs, PCDFs and PCDDs. Office workers, for example, may be exposed to these chlorinated compounds via inhalation of contaminated particulates and vapors, dermal contact with contaminated surfaces, and incidental ingestion of dusts. A wide range of re-entry or cleanup levels have been developed for PCDDs and PCBs to protect workers who re-occupy a building following a PCB fire. Re-entry criteria have been used by property owners and regulatory agencies to determine whether the building is safe to re-occupy or to determine the extent of needed remediation. This paper presents a mass balance approach to deriving risk-based re-entry surface and air criteria for PCBs and PCDD/PCDFs. These criteria were based on a lifetime risk level of 10(-5), recent toxicological data on PCDDs and PCBs, and plausible exposure scenarios. Our analysis suggests that 125 ng/m2 2,3,7,8-TCDD TEQ for surfaces and 10 pg/m3 for air are acceptable. Based on Aroclor 1260, risk-based re-entry criteria for PCBs on surfaces and in air were 750 micrograms/m2 and 0.1 microgram/m3, respectively. In comparison to most previous guidelines, these risk-based criteria are less stringent, but can still be considered conservative. The surface criteria are 5 to up to 125 fold higher than previous guidelines. Air criteria range up to 5 times higher than criteria used at past PCB fire sites. Air concentrations associated with these were modeled and were negligible. For PCBs in air, the NIOSH guideline of 1 microgram/m3 is also appropriate for occupational settings.