Groundwater and

Subsidence

Groundwater and

Subsidence

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

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

Land Subsidence: The sinking of land or “settling” due to the extraction materials

Land Subsidence: The sinking of land or “settling” due to the extraction materials

In-proper soil compaction inthe year 1173 led to the“leaning” tower of Pisa

“air” in the soil void spaces forced out

creating subsidence

In-proper soil compaction inthe year 1173 led to the“leaning” tower of Pisa

“air” in the soil void spaces forced out

creating subsidence

Subsidence – removal of a coal bedSubsidence – removal of a coal bed

What if groundwater is removed from the subsurfaceWhat if groundwater is removed from the subsurfaceFactors affecting groundwater Factors affecting groundwater subsidencesubsidence

What if groundwater is removed from the subsurfaceWhat if groundwater is removed from the subsurfaceFactors affecting groundwater Factors affecting groundwater subsidencesubsidence

Porosity:Porosity: the amount of voidthe amount of void

spaces available to spaces available to store waterstore water

Expressed as a %Expressed as a %

Porosity:Porosity: the amount of voidthe amount of void

spaces available to spaces available to store waterstore water

Expressed as a %Expressed as a %

10% -20%10% -20%

30%-50%30%-50%

Permeability:Permeability:the ability for water to movethe ability for water to move

(transmit) through the media (transmit) through the media

Permeability:Permeability:the ability for water to movethe ability for water to move

(transmit) through the media (transmit) through the media

Rock Type PorositiesRock Type Porosities

Well sortedsandstone and gravel

Well sortedsandstone and gravel

HighHigh

ClayClayHigh

“hard togive up”

High“hard togive up”

Poorly sortedsands

Cementedsands

Limestone

Shale

Poorly sortedsands

Cementedsands

Limestone

Shale

LowLow

Typical stratgraphic section of theSan Joaquin Valley

Typical stratgraphic section of theSan Joaquin Valley

SandstoneSandstone

Sandstone / siltstoneSandstone / siltstone

Sandstone / siltstone / shaleSandstone / siltstone / shale

19151915

19601960

What will happen when groundwater is removed???What will happen when groundwater is removed???

Example of Land SubsidenceExample of Land Subsidence

300300

600600

12001200

18001800

24002400

Pumping groundwaterfrom 1934 - 1967Pumping groundwaterfrom 1934 - 1967

Line of equal elevationof land subsidenceUnits of millimeters (mm)

Line of equal elevationof land subsidenceUnits of millimeters (mm)

300

600

1,200

1,800

2,400

San Francisco Bay

Silver CreekFault

Line of equal long-termland subsidence (1934-67)(intervals of mm) A

A’1,200

2,400

300300

600600

900900

1,2001,200

1,5001,500

1,8001,800

2,1002,100

2,4002,400

AA A’A’

Vertical ScaleVertical Scale Profile ConstructionProfile Construction

Groundwater: accumulation of water below the surface through infiltration processes

Groundwater: accumulation of water below the surface through infiltration processes

GroundwaterGroundwater

Infiltration into the soilInfiltration into the soil

Groundwater Contamination

• groundwater is contaminated by outside sources that infiltrate through the subsurface

• petroleum (gasoline)• agriculture products• mine waste• dump waste

Groundwater Contamination

• groundwater is contaminated by outside sources that infiltrate through the subsurface

• petroleum (gasoline)• agriculture products• mine waste• dump waste

Migration of groundwater (movement) usingflow linesMigration of groundwater (movement) usingflow lines

water table contour lineswater table

contour lines

GW flow lines

Flow lines always flow perpendicular tocontour lines !!!!!!!Flow lines always flow perpendicular tocontour lines !!!!!!!