1. Groundwater
and
Subsidence

2. Groundwater Subsidence Objectives: to use principles of groundwater
flow and determine if various areas
are affected by environmental pollution
to correlate groundwater withdrawal and
land subsidence with routine human
practices

3. Land Subsidence: The sinking of land or “settling” due to the
extraction materials
In-proper soil compaction in
the year 1173 led to the
“leaning” tower of Pisa
“air” in the soil void
spaces forced out
creating subsidence

4. Subsidence – removal of a coal bed

5. What if groundwater is removed from the subsurface
Factors affecting groundwater
subsidence
Porosity:
the amount of void
spaces available to
store water
Expressed as a %
10% -20%
30%-50%
Permeability:
the ability for water to move
(transmit) through the media

6. Rock Type Porosities High High “hard to Clay give up” Low Well sorted
sandstone
and gravel
High
High
“hard to
give up”
Clay
Poorly sorted
sands
Cemented
Limestone
Shale
Low

7. Typical stratgraphic section of the
San Joaquin Valley
1915
Sandstone
Sandstone / siltstone
1960
Sandstone / siltstone / shale
What will happen when
groundwater is removed???

8. Example of Land Subsidence
Pumping groundwater
from
300
600
1200
1800
2400
Line of equal elevation
of land subsidence
Units of millimeters (mm)
Example of Land Subsidence

9. A’ A Profile Construction A A’ Silver Creek Fault
300
Silver Creek
Fault
600
San Francisco Bay
1,200 A’
1,800
2,400
Line of equal long-term
land subsidence ( )
(intervals of mm)
1,200 A
2,400
Vertical Scale
Profile Construction
300
600
900
1,200
1,500
1,800
2,100
2,400 A A’

10. Groundwater: accumulation of water below the
surface through infiltration
processes
Infiltration into the soil
Groundwater

11. Groundwater Contamination
groundwater is contaminated by outside
sources that infiltrate through the subsurface
petroleum (gasoline)
agriculture products
mine waste
dump waste

12. Migration of groundwater (movement) using flow lines
water table
contour lines
GW flow lines
Flow lines always flow perpendicular to
contour lines !!!!!!!