This thesis describes in-situ flow tests on bentonite borehole plugs installed in granite, as well as laboratory experiments on similar plugs. Prior to sealing, the hydraulic conductivity of the boreholes is tested. These measurements, together with core logs and borehole videologs, permit the selection of suitable seal test intervals. Standard waterwell sealing bentonite products and emplacement procedures are used for borehole sealing. Transient (short-term) and steady-state (long-term) testing determines the sealing performance of the plugs (although the premature termination of the "steady state" testing precluded full data collection). Laboratory and field experiments confirm the great difficulty of obtaining accurate performance values for bentonite plugs as installed, due to the simultaneous saturation, swelling, and consolidation effects. Conventional installation of readily available seals can provide adequate borehole seals. Bentonite plugs of this type are heterogeneous and weak. Improved testing procedures and analyses are needed if actual conductivity values are to be obtained in a reasonable testing time.
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