Slide 17 of 35
Notes:
Generalized flow paths for the 1996 Happy Isles Rockslide
This diagram illustrates the most probable groundwater flow paths (regardless of rockfall location) from the temporary leach field that existed in 1996 (removed in 1997) based on the nature of the soil and the orientations of the dominant discontinuities.
Note that the most probable groundwater flow paths clearly deliver the waste water from the leach field directly to the 1996 rockfall source areas.
The granular soil (grus) derived from the weathering granite allows water to percolate downward to the bedrock where it encounters the dominant discontinuities dipping to the east and follows those shallow open features to the cliff face emerging at the rockfall source area. Groundwater flow in a dense granitic rock will be forced to follow cracks and fractures in a down dip direction.
Pictures found elsewhere in this report show significant amounts of water seeping from the rockfall source area in 1996 after the slide and in 1997.
This wastewater treatment system was removed in August of 1997 and by October of 1997 the rockfall source area was dry, as shown in later photographs. It has been dry on every subsequent visit by the authors.
This indicates a direct relationship between the wastewater system and the water seeping from the rockfall site.
