Groundwater

BIG Idea: Precipitation and infiltration contribute to groundwater, which is stored in underground reservoirs until it surfaces as a spring or is drawn from a well.Precipitation and infiltration contribute to groundwater, which is stored in underground reservoirs until it surfaces as a spring or is drawn from a well.

Infiltration: process of water moving into the soil/groundprocess of water moving into the soil/ground to penetrate, enter or gain accessto penetrate, enter or gain access

I. Water Beneath the Surface Groundwater: underground water that fills almost all of the pores in rock and sediment

Aquifer: a body of rock that can store water and also let water flow through

AQUIFER Think of an AQUIFER as a… spongelarge, horizontal sponge that absorbs and transports water along its length

A. Rock Properties that Affect Groundwater  Porosity  Permeability

1. Porosity: percentage of open spaces in a rock or sediment

FACTORS THAT INFLUENCE POROSITY: (a) SORTING: amount of uniformity in particle size HIGH pore spaceLOW pore space

(b) SHAPE: (b) SHAPE: rounder particles = more porous (c) PACKING: (c) PACKING: loosely packed = more porous

2. Permeability: how freely water flows through open spaces in a rock (the pores must be connected) Impermeable – water can NOT flow through

Can something be porous but impermeable? The cork end is red because the grape juice went into it. Does this mean it is porous?The cork end is red because the grape juice went into it. Does this mean it is porous? If you turn the bottle upside down will it leak? Is the cork permeable?If you turn the bottle upside down will it leak? Is the cork permeable?

B. Zones of Groundwater 1. Zone of Saturation: the layer of ground where all the pores are filled with water.

2. Water Table: upper surface of the zone of saturation

3. Zone of Aeration: upper region, where water is both in the soil and seeping down to the water table.

Zone of Aeration ►

Capillary Action: ability of water to rise UP the soil. Smaller particle size = greater capillarity

Capillary Fringe: middle layer, between the water table and the zone of aeration.

C. MOVEMENT OF GROUNDWATER Depends on: 1.Permeability of the aquifer ↑ permeability = ↑ velocity 2.Gradient of the water table Gradient = steepness of the slope ↑ gradient = ↑ velocity

II. Wells and Springs Water Table: upper layer of rocks with all pores filled with water.Water Table: upper layer of rocks with all pores filled with water.

A. Ordinary Well: A hole dug below the water table which fills up with water.

Cone of Depression: lowered area of the water table due to pumping

B. Artesian Wells: water flows freely with no pumping Underground water under pressure (between two impermeable rock layers) rises to the surface Water is naturally filtered as it passes through porous rock and seeps to surface

III. Groundwater and Chemical Weathering A.Caverns: rocks rich in calcite (limestone) slowly dissolved by carbonic acid. Hard water = many dissolved minerals (Ca, Mg, Fe)Hard water = many dissolved minerals (Ca, Mg, Fe) Soft water = few dissolved mineralsSoft water = few dissolved minerals

Luray Caverns, VA

Formation of a CaveFormation of a CaveFormation of a CaveFormation of a Cave

1. Stalactites: water with dissolved calcite runs from a cave’s ceiling and solidifies downward.

2. Stalagmites: calcite rich water drips on the cave’s floor and builds upward.

If the two connect, then it forms a column.

3. Natural Bridge: when the roof of a cavern collapses in several places leaving an arch- shaped rock.

B. KARST TOPOGRAPHY regions where chemical weathering by groundwater is now visible at the surface regions where it is humid and there are limestone formations near the surface Virginia, Kentucky, Tennessee, Indiana, and Florida have Karst Topography

1. Sinkholes (the main feature of Karst Topography)

How do sinkholes form? Rain seeps through soil and absorbs carbon dioxide and reacts with decaying vegetationRain seeps through soil and absorbs carbon dioxide and reacts with decaying vegetation Acidic water is createdAcidic water is created Water moves through spaces and cracks undergroundWater moves through spaces and cracks underground Limestone is slowly dissolved, creating network of cavities and voidsLimestone is slowly dissolved, creating network of cavities and voids Pores and cracks enlargePores and cracks enlarge Land surface above collapses or sinksLand surface above collapses or sinks

2. Streams that disappear in the ground Like Lewis Creek in Staunton

3. Caverns and Caves