Water and the Hydrogeology of Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 89

• Fractures caused by differential compaction
• Fractures caused by freeze-thaw cycles
• Fractures caused by vegetative root fragments
• Bioturbation
• Vugs (small to medium-sized cavities inside rocks), fissures, or solution cavities
caused by dissolution from migrating waters or other chemicals that dissolve or
precipitate minerals
Freeze and Cherry (1979) note the extent of freeze-thaw within some soils in colder cli-
mates can reach up to 9 m (30 ft) beneath the surface. This may be particularly significant
when examining the integrity of a confining unit at shallow depths. Any of the above
listed types of secondary porosity can also influence the integrity of an aquiclude from
shallow to sometimes significant depths beneath the ground surface. Figures 3.28 and 3.29
show a root fragment in a clayey soil and a vertical fracture in a clayey soil, respectively.
Root fragment
FIGURE 3.28
Root fragment in a deposit composed of clay. (Photo by Daniel T. Rogers.)
Vertical fracture
FIGURE 3.29
Vertical fracture in a sediment composed of clay. (Photo by Daniel T. Rogers.)