Groundwater Midterm

What process moves water from the surface to the subsurface?

Infiltration

What process moves water within the subsurface?

Percolation

What process moves water from ground water to the atmosphere?

Evapotranspiration

What process moves water from glaciers to the atmosphere?

Sublimation

What process moves water from the biosphere to the atmosphere?

Transpiration

What process moves water from ground water to streams?

Seepage

Weight

Mass x gravity(9.81 m/s²)

Porosity

Proportion of a rock or sediment that is open space, not necessarily connected

Permeability

Ability of a rock to allow the passage of fluid through material

Measure of the rate at which water can flow through a rock.

Which has a greater effect on porosity, grain size or packing?

Packing, the more packed the less space is between particles.

Which has a greater effect on porosity, grain size or sorting?

Sorting because larger grain sizes can be sorted in such a way to eliminate pores.

Transmissivity

the ability of a medium to allow the passage of water, radiation, or light, and the ease with which groundwater flows through an aquifer

Transmissivity Equation

T = Kb

K= the coefficient of permeability

b= thickness of the aquifer

Units= length² / time

Transmissivity (Theim Equation)

Hydraulic Conductivity

a measure of how easily water or other fluids can pass through porous materials, soils, or rocks. It's also known as the coefficient of permeability.

= K

Volume

ft³ or m³

Hydrologic Budget Equation

P = Et + RO + GWS

Darcy’s Law

Flow of fluid through a porous medium

Q= discharge

K= hydraulic conductivity

Specific yield

the ratio of the volume of water that a saturated rock or soil will yield by gravity to the total volume of the rock or soft.

Specific discharge

the volume of water that flows through a unit cross-sectional area of porous media per unit time.

Isotropic

Have the same index of refraction in all directions

ISO=equal

Uniformitarianism

The present is key to the past

Population

Growth is the biggest problem facing humanity

Pleistocene

2 m years ago - 10,000 years ago

Homogeneous

All the same

Holocene

the name given to the last 11,700 years* of the Earth's history

Pathways

Flow from high to low in broad looping curves from recharge areas to discharge areas in unconfined aquifers

In confined aquifers movement is controlled by the geometry of rock units

Speed of groundwater

Few cm to m per day

Fluid potential

Water flows through arc and soil under the influence of…

Varies from one area/ spot to another

Flow nets

Are used to show ground water flow

Exponential lines

Are roughly perpendicular to flow lines

• Will never intersect

• They get closer together closer to the surface or in a river were water flows faster

Artesian pressure

Allows groundwater to flow upward

Chicot Aquifer System

• Largest Aquifer in Louisiana

• Very thick, 500 m (1500 ft)

• Lower half filled with salt water

• Rocks: massive sandstone interceded with clay layers tilted south so we get water North of us

• Age: Pleistocene

Problems with the Chicot Aquifer

• Over 19,000 “non-hazardous” waste pits

• Over-pumping

Hydrology

The study of waters of the earth; rivers, lakes, groundwater

Hydrogeology

Interaction of water with geological materials

Geohydrology

An engineering term

Where is the water?

Salt water- 96%

Fresh water- 4%

• Glaciers- 3%

• Groundwater- 1%

• Lakes and rivers- 0.009%

• Atmosphere- 0.001%

• Biosphere- 0.0001%

Finding Evaporation

1) Use standard pan-evaporation data

2) Use a soil psychrometer

3) Use model estimates

4) Use a “nomograph”

5) Use a Thornthwaite Method w/T

Aquifer

Porous and permeable layer that contains and produces groundwater

Aquiclude

Or aquitard

Impermeable layer that blocks flow

Unconfined Aquifer

The permeable layer extends to the surface.

It consists of an unsaturated zone separated from the saturated zone by the groundwater table.

Confined aquifer

The permeable layer is overlain and underlain by a less permeable layer (aquitard or aquiclude)

Water Table

Is a subdued reflection of the topography

Pressure Surface

The level to which water will rise in wells in confined aquifers.

1m=

3.28 feet

1 acre =

43,560 ft

1 cm =

0.0328 feet

1 foot=

30.48 cm

Area

Pie*r²

Difference between transmissivity and hydraulic conductivity

transmissivity is the total flow of water through an aquifer, while hydraulic conductivity is the rate of flow through a unit cross-sectional area

1 mile=

5,280 feet

Four types of groundwater contamination

Salt water intrusion, agricultural products,

Two basic processes that operate to transport solutes. How do they relate to dispersion and retardation?

Recharge areas

Topography: high

Water table depth: deep

Vadose zone size: thick

GW movement: down

Flow line configuration: diverge

Discharge area

Topography: lows

Water table depth: shallow

GW movement: up

Flow line configuration: converge

Other clues: wet, vegetated

2. Regional

Recharge area size: small

Depth:width (ratio): 1:2

Water volume: bigger

Temperature: hotter

Composition (TDS): High

Local

Recharge area size: big

Depth:width (ratio): 1:5-1:10

Water volume: smaller

Rate of water movement: quick

Temperature: cooler

Composition (TDS): fresh

Chico aquifer

• Southwest Louisiana

• Sandstone with clay layers

• Pleistocene

• Faults

• 500 meters

• Flows south a few cm a day

Flow systems

What happens to flow systems as topography changes from flat, gently tilted to more irregular and “hillier”?

GWD increase, hinge-lines increase, and there will be more individual recharge and discharge area.

Reductive desorption

a process where arsenic, often bound to iron oxides in soil or sediment, is released into water due to a reduction in the oxidation state of the iron, causing the arsenic to detach and become mobile in the water

Hydrologic Gradient

Dh/dl