Snow (1968) calculated fracture apertures in granite,gneiss and metavolcanic rocks from measurements of permeability derivedfrom packer tests in drill holes. Computed apertures ranged from 75–400 μmin the upper 10 m of bedrock, decreasing to 50–100 μm at 15–60 m depth.Similarly, Gale et al. (1982) estimated fracture apertures between 5 and 20 μmat depths of several hundred metres in granites at Stripa, Sweden. Rocha andBarroso (1971) measured the apertures of open fractures in granite using aspecially designed coring method. The average fracture aperture was 400 μmat 2.5–4.5 m depth into the bedrock, decreasing to 100 μm at 13.5 – 14.5 m(Trainer, 1988).