GEO LAB PRAC 2

What is Groundwater?

Water stored below Earth's surface in soil, sediment, and rock.

What is an Aquifer?

An underground reservoir that stores groundwater. Good aquifers are typically porous and permeable, such as:

• Gravel

• Sand

• Sandstone

• Some fractured or dissolved rocks

What is an Aquitard?

A layer that stores small amounts of water but does not transmit it well.

What is an Aquiclude?

A layer that does not store significant water and does not transmit it. Common materials include:

• Clay

• Shale

• Other non-porous rocks

What is Porosity?

The amount of empty space in a material that can hold fluids.

What is Permeability?

How easily fluids move through a material. High porosity does not always mean high permeability — pores must also be well connected.

What are the hydrogeologic roles of sandstone, clay/shale, and karst limestone?

• Sandstone — High porosity/permeability; good aquifer

• Clay or shale — Low porosity/permeability; good aquitard or aquiclude

• Karst limestone — Variable porosity, very high permeability along conduits; transmits water rapidly

What is the Water Table?

The top of the saturated zone, where pores and fractures are fully filled with water. Its depth changes with season, climate, and location.

How does Groundwater Flow?

From higher elevation or pressure toward lower elevation or pressure. Flow is perpendicular to water-table contours.

What is Karst & How does it form?

Karst is a landscape formed when slightly acidic water dissolves calcite in limestone. Features include:

• Sinkholes

• Caves

• Springs

• Disappearing streams

Why does karst pose a groundwater contamination risk?

Because water (and contaminants) travel through conduits rather than slowly through pore spaces, allowing rapid movement.

What is the equation for hydraulic gradient?

Hydraulic Gradient = Change in elevation ÷ Horizontal distance

What is the equation for flow rate (Velocity)?

Flow Rate (Velocity) = Distance ÷ Time

What are monitoring wells used for?

• Sampling groundwater

• Measuring water levels

• Detecting contamination

• Tracking plume migration

What are injection wells used for?

To add fluids to groundwater systems, such as:

• Dye tracers

• Wastewater

• Brine

• Other substances

How is tracer dye used in groundwater studies?

It is injected into the system to determine the direction and speed of groundwater flow.

How are contamination plumes mapped in the lab?

Concentration data from monitoring wells are collected over time, transferred to well-field diagrams, and contoured at multiple time intervals to show plume movement and concentration changes.

What is the equation for hydraulic conductivity?

Hydraulic Conductivity = Velocity ÷ Slope

What is the equation for discharge?

Discharge = Cross-Sectional Area × Velocity
where Cross-Sectional Area = Width × Height of the aquifer layer

What is the slope equation used in groundwater calculations?

Slope = Change in elevation ÷ Distance

What factors control coastline shape?

• Rock hardness (hard rock resists erosion)

• Sediment supply from rivers, currents, and local erosion

• Wave energy and wind

• Sea-level change and tectonics

• Storms and organisms

• Human activity

What is the difference between emergent and submergent coastlines?

• Emergent (advancing) — depositional processes add sediment; coastline grows seaward

• Submergent (receding) — erosional processes remove sediment; coastline retreats landward and floods

List of Depositional coastal landforms

• Beach — gently sloping accumulation of sand or gravel

• Delta — fan-shaped sediment deposit at a river mouth

• Barrier island — long, narrow island parallel to the mainland

• Reef — coral formation running parallel to a shoreline

List the erosional coastal landforms

• Wave-cut cliff — cliff eroded by wave action

• Wave-cut platform — flat bench at sea level formed by wave erosion

• Marine terrace — elevated wave-cut platform formed by uplift or sea-level regression

What are the three types of coastal wetlands?

• Estuary — partially enclosed body of brackish water where freshwater meets seawater

• Tidal flat — muddy or sandy area covered at high tide and exposed at low tide

• Salt marsh — coastal marsh flooded by seawater during high tide

What is storm surge and why is it dangerous?

Storm surge is an abnormal rise in seawater level caused mainly by winds pushing water onshore during a storm or hurricane. It is most hazardous when it occurs during high tide, dramatically increasing coastal flooding.

What is leachate?

A highly contaminated liquid formed when water percolates through waste in a landfill. It can contain:

• Dissolved organic matter

• Metals

• Ions

• Hazardous substances

Why is leachate a good conductor of electricity?

Because it is rich in ions, which carry electric current effectively.

What are the key design features of a sanitary landfill?

• Buffer zones

• Plastic liners

• Clay caps

• Monitoring systems

What is electrical resistivity?

A material's ability to resist the flow of electric current. Conductivity is its opposite. Low resistance (high conductivity) in a landfill survey can indicate leachate leakage.

How does the electrical resistivity method detect a landfill leak?

A battery sends current into the ground and a voltmeter measures voltage differences. Zones of abnormally low resistance (high conductivity) indicate leachate, with higher voltage values closer to the leak location.

How to map a leaky landfill?

• Map a leak-free landfill first to establish a baseline electrical-potential pattern

• Map the leaky landfill to identify zones of abnormal electrical behavior

• Construct contour maps of electrical potential

• Use contour lines and flow lines to infer leak location and current flow direction

What is a contamination plume?

A 3D zone of contaminated air, water, or soil spreading outward from a single source (e.g., leaking tanks, industrial discharge, leaking landfills). Plumes form concentration gradients — highest near the source, dissipating outward.

What are structure contours?

Lines connecting points of equal elevation or depth on a subsurface geologic surface (e.g., a fault, formation, or the water table). They are similar to topographic contours but represent subsurface features.

What is a 3-Point problem?

A method used to determine the orientation of a planar subsurface surface from three well data points.

How do you solve a 3-Point Problem?

• Plot and label the depths of three wells on the map

• Draw a line between the deepest and shallowest points

• Estimate where the same depth as the mid-depth well falls on that line

• Connect equal-depth points to create a structure contour line (this gives the strike)

• Dip is perpendicular to strike, pointing toward lower elevations

• Groundwater flow direction follows the dip direction

• Extrapolate additional depth contours from the first structure contour

Relationship between dip & strike?

Dip is perpendicular to strike and points in the direction of lower elevations (downslope). Groundwater flow follows the dip direction.

What was the goal of the Environmental Game?

To delineate the direction and concentration of the pollution plume from the Meadowlands Landfill and identify which town would be affected, while spending the least amount of money.

What was the most useful strategy in the Environmental Game?

Drilling wells near the landfill in the direction of groundwater flow (determined by the 3-point problem) to efficiently locate the plume.