The initial geotechnical investigation included 30 boreholes up
to 10.7 m (35 ft) deep. The subsurface soils were observed to consist
of up to 3.7 m (12 ft) of silty-sandy clay underlain by 4.3 m
(14 ft) of weathered claystone, and claystone bedrock beyond the
maximum boring depth of 10.7 m (35 ft). The bedrock dips to the
east at approximately 20°. Several seams of gypsum ranging from
1.6 to 12.7 mm (1=16 to 1=2 in:) in thickness were seen in all theboreholes. Joints and fractures were generally high angle to nearly
vertical.